Displays

Age of air is an idealized tracer often used as a measure of the stratospheric circulation. We will show how to quantitatively relate age to the diabatic circulation and the adiabatic mixing. As it is an idealized tracer, age cannot be measured itself and must be inferred from other tracers. Typically, the two primary trace gases used are sulfur hexafluoride and carbon dioxide. Other tracers have a compact relationship with age, however, and can also be used to calculate age. We will discuss a range of tracer measurements from both satellites and in situ, including sulfur hexafluoride, carbon dioxide, nitrous oxide, methane, and the ratio of argon to nitrogen. We will compare the age derived from these different species, including different calculation methods and caveats, and compare with modeled ideal age and trace gas concentrations. We conclude by showing the strength of the diabatic circulation and the adiabatic mixing calculated from these trace gas calculations.

How to cite: Linz, M., Birner, B., Plumb, A., Gerber, E., Haenel, F., Stiller, G., Kinnison, D., and Neu, J.: Age of Air in the Stratosphere from Observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12704, https://doi.org/10.5194/egusphere-egu2020-12704, 2020.

The first and only global data set of mean age of stratospheric air (AoA) with dense day and night coverage has been derived from MIPAS observations by analysis of the spectral signature of SF₆ (Stiller et al., 2008, 2012; Haenel et al., 2015). Since SF₆ is a tracer with no sinks in the troposphere and stratosphere and an almost linearly increasing atmospheric abundance, it is often used to derive information on stratospheric transport and mixing due to the Brewer Dobson Circulation, quantified usually as mean age of stratospheric air (AoA). The global data sets of AoA derived so far from MIPAS observations, on basis of spectroscopically measured absorption cross sections by Varanasi et al. (1994), had a high bias in the middle to upper stratosphere compared to balloon-borne in situ observations from the 1990s. By applying a new spectroscopic data set measured in the laboratory recently (J.J. Harrison, to be published), we show that part of the high bias in AoA can be removed, and the residuals between measured and modelled atmospheric spectra can be decreased significantly. In this presentation we discuss the new SF₆ and AoA distributions, variablilities and trends, and compare to previous versions and independent in situ observations. 

References:

Haenel, F. J., Stiller, G. P., von Clarmann, T., Funke, B., Eckert, E., Glatthor, N., Grabowski, U., Kellmann, S., Kiefer, M., Linden, A., and Reddmann, T.: Reassessment of MIPAS age of air trends and variability, Atmos. Chem. Phys., 15, 13161-13176, https://doi.org/10.5194/acp-15-13161-2015, 2015.
Stiller, G. P., von Clarmann, T., Höpfner, M., Glatthor, N., Grabowski, U., Kellmann, S., Kleinert, A., Linden, A., Milz, M., Reddmann, T., Steck, T., Fischer, H., Funke, B., López-Puertas, M., and Engel, A.: Global distribution of mean age of stratospheric air from MIPAS SF6 measurements, Atmos. Chem. Phys., 8, 677-695, https://doi.org/10.5194/acp-8-677-2008, 2008.
Stiller, G. P., von Clarmann, T., Haenel, F., Funke, B., Glatthor, N., Grabowski, U., Kellmann, S., Kiefer, M., Linden, A., Lossow, S., and López-Puertas, M.: Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period, Atmos. Chem. Phys., 12, 3311-3331, https://doi.org/10.5194/acp-12-3311-2012, 2012.
Varanasi, P., Li, Z., Nemtchinov, V., and Cherukuri, A.: Spectral Absorption–Coefficient Data on HCFC-22 and SF6 for Remote– Sensing Applications, J. Quant. Spectrosc. Radiat. Transfer, 52, 323–332, 1994.

How to cite: Stiller, G. P., Harrison, J. J., Haenel, F. J., Glatthor, N., Kellmann, S., and von Clarmann, T.: Improved global distributions of SF6 and mean age of stratospheric air by use of new spectroscopic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2660, https://doi.org/10.5194/egusphere-egu2020-2660, 2020.

Ozone in the extrapolar lower stratosphere is currently declining for reasons that are not well understood. Iodine is emitted mostly from marine sources, and changing iodine emissions provide a possible chemical reason for why ozone in the lower stratosphere continues to decline (Koenig et al., 2020). Previous stratospheric measurements had detected iodine qualitatively in particles. More recently, IO observations in the daytime tropical tropopause layer (TTL) have suggested that between 0.25 to 0.70 pptv Iy are injected into the stratosphere, which is 1.6 to 3.5 times the WMO2014 upper limit. These indirect observations have led to revised estimates of 0 - 0.8 pptv Iy stratospheric injection in the WMO2018 report. This presentation discusses first quantitative measurements of IO radicals and of submicron particulate iodine from aircraft in the stratosphere that support 0.77 pptv Iy stratospheric injection. Our observations support the WMO2018 upper limit estimate, and clearly are incompatible with zero iodine injection. The implications of the obseved iodine concentrations for ozone loss in the lower stratosphere are discussed, also in light of climate records that find increasing iodine in recent decades, observed ozone trends, and ongoing and future research needs to better quantify iodine's contribution to explain these trends. 

How to cite: Volkamer, R., Koenig, T., Campuzano-Jost, P., Saiz-Lopez, A., Jimenez, J., Fernandez, R., Kinnison, D., and Cuevas, C.: Quantitative Detection of Iodine in the Stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21998, https://doi.org/10.5194/egusphere-egu2020-21998, 2020.

The biomass burning season in America was exceptionally intense during summer 2019. Particularly in the subtropics biomass burning potentially contributes significantly to the trace gas budget of the upper troposphere and can affect chemistry and composition far from the source.

During the SOUTHTRAC mission, which took place in September and November 2019, several cross sections from the equator to the southern tip of south America were flown at typical altitudes of 13-14 km. During the northbound flight on October, 7^th 2019 massive enhancements of pollutants were observed at these altitudes. Notably, in-situ observations show continuously elevated CO values exceeding 200 ppbv over a flight distance of more than 1000 km. These massive enhancements were accompanied by largely elevated NO and NO_y as well as CO₂ and could be attributed to the large fires in South America during this time. Observations of C2H₂ and PAN from GLORIA show, that pollution covered a layer extending from 8-9 km to the flight level at 13 km.

Comparing the tracer observations to previous flights in exactly the same region three weeks earlier, we could estimate the ozone production due to the biomass burning. Based on first results we estimate ozone production in the polluted air masses up to 30-40 ppbv in the UT which is almost 40% of the observed ozone mixing ratio. Given the large extent of the polluted area over 15 degrees of latitude this may have an impact on the local energy budget of the tropopause region.   

How to cite: Hoor, P., Kunkel, D., Lachnitt, H.-C., Bozem, H., Bense, V., Grooß, J.-U., Ungermann, J., Engel, A., Zahn, A., Ziereis, H., Friedl-Vallon, F., Johansson, S., Sinnhuber, B.-M., Riese, M., and Rapp, M.: Empirical ozone production in the subtropical UTLS from South American biomass burning during SOUTHTRAC, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12585, https://doi.org/10.5194/egusphere-egu2020-12585, 2020.

Bromine greatly influences the UT/LS ozone concentrations, however the transport of bromine across the tropical tropopause layer and in particular across the extratropical tropopause is not well quantified. Air-borne measurements of atmospheric trace gases such as organic and inorganic bromine along the tropopause are studied during the WISE (Wave-driven ISentropic Exchange) research campaign over the northern Atlantic and western Europe from September 13 - October 21, 2017. The remote sensing instrument mini-DOAS (Differential Optical Absorption Spectroscopy) is mounted on the HALO (High Altitude and LOng range) aircraft and measures BrO (O₃, NO₂ among other trace gases). The novel scaling method is applied to infer the target gas BrO mixing ratios from slant column densities using in-situ O₃ measurements from the FAIRO instrument (operated by KIT) as the scaling gas. For each flight, the inferred mixing ratios are directly compared with CLaMS (Chemical Lagrangian Model of the Stratosphere) simulated curtains of the trace gases along the flight path. The partitioning coefficient of inorganic bromine from CLaMS and all relevant organic halogen species and air mass ages (SF₆, CO₂) from the GhOST-MS instrument (operated by UFra) are used to determine the total bromine budget along the UT/LS. A climatology of organic, inorganic and total bromine is constructed with respect to the extratropical tropopause as well as the air mass ages. This indicates the interplay of bromine transport across the extratropical tropopause and of the transport of air via the lower branch from the tropics as well as potential losses of inorganic bromine by uptake onto and sedimentation of ice particles.

How to cite: Rotermund, M., Schreiner, B., Kluge, F., Hüneke, T., Engel, A., Schuck, T., Kerber, T., Grooß, J.-U., Zahn, A., and Pfeilsticker, K.: Inorganic and organic bromine measurements around the extra-tropical tropopause: Insights into total stratospheric bromine, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7507, https://doi.org/10.5194/egusphere-egu2020-7507, 2020.

The vertical distribution and seasonal variation of water vapour volume mixing ratio (H₂O VMR), relative humidity with respect to ice (RH_ice) and particularly of regions with ice-supersaturated air masses (ISSR) in the extratropical upper troposphere and lowermost stratosphere are investigated at northern mid-latitudes over the regions Eastern North America, the North Atlantic and Europe for the period 1995 to 2010.

Observation data originate from regular and continuous long-term measurements of H₂O VMR, temperature and RH_ice by instrumented passenger aircraft in the framework of the European research program MOZAIC which is continued as European research infrastructure IAGOS (from 2011; see www.iagos.org). The observation data are analysed with respect to the thermal and dynamical tropopauses, as provided by ERA-Interim. Additionally, collocated O₃ observations from MOZAIC are used as tracer for stratospheric air masses.

Our key results provide in-depth insight into seasonal and regional variability and tropospheric nature of ice-supersaturated air masses at various distances from the tropopause layer. For the vertical distribution and seasonal variation of ISSR occurrence we show a comparison of our results to radio soundings and to satellite observations of cirrus cloud occurrence from AIRS and TOVs Path B instruments. Finally, for all three regions, we investigate the trends and the dependencies of ISSR occurrence on the North Atlantic Oscillation (NAO) index.

How to cite: Petzold, A., Rohs, S., Rütimann, M., Neis, P., Florian, B., Herman, S., Martina, K., Nicole, S., Peter, S., Philippe, N., and Andreas, W.: Vertical distribution, seasonality and troposphericity of ice-supersaturated air masses in the northern mid-latitudes from regular in-situ observations by passenger aircraft, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8992, https://doi.org/10.5194/egusphere-egu2020-8992, 2020.

Ozone pollution is currently a serious environmental issue in China. Most of studies have attributed the surface ozone pollution over China to the strong photochemical production from anthropogenic sources. As another important source of tropospheric ozone, the stratospheric intrusion (SI), however, has been less concerned. This study investigates the SI events over the Yangtze River Delta in eastern China using the newest ERA5 (the fifth generation of ECMWF atmospheric reanalysis) meteorological and ozone data, the In-service Aircraft for a Global Observing System (IAGOS) ozone profiles and the station-based ground-level ozone measurements. Results indicate that SI plays important roles in spring and summer ozone pollution episodes over the Yangtze River Delta, eastern China. Based on CAM-Chem (the Community Atmosphere Model with Chemistry) and LPDM (Lagrangian Particle Dispersion Modeling) model simulations, we found that deep SIs contribute ~15 ppbv in spring and ~10 ppbv in summer to surface ozone variations in eastern China. A deep SI event occurred in 2018 spring associated with a strong horizontal-trough, which brought ozone-rich air from the stratosphere to the troposphere and resulted in severe surface ozone pollution over the Yangtze River Delta. From 7-year statistics, we found that strong SI events during summer are associated with a cyclonic valley between the South Asian High and the Subtropical High, accompanied by downward fast transport of ozone from the stratosphere to the troposphere. Our results provide important information for surface ozone prediction and control in eastern China.

How to cite: Wang, W.: Impacts of Stratospheric Intrusion on Surface Ozone over Eastern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6898, https://doi.org/10.5194/egusphere-egu2020-6898, 2020.

The Brewer-Dobson Circulation (BDC) plays a major role in the stratospheric dynamics in terms of tracer transport through the mean residual meridional advection and the isentropic 2-way mixing.
The climatological BDC in the Whole Atmosphere Community Climate Model (WACCM) is separated in its components and evaluated through a comparison with a chemical reanalysis of the Aura Microwave Limb Sounder version 2 (BRAM2) and with a chemistry-transport model driven by four modern reanalyses (ERA-Interim, JRA-55, MERRA and MERRA2). The BDC seasonal means and climatological annual cycle are addressed using the Transformed Eulerian Mean (TEM) analysis of the long-lived tracer N2O. The N2O TEM budget terms considered in this study are the vertical residual advection and the horizontal two-way mixing terms.
WACCM presents a general underestimation of the horizontal mixing term in the wintertime Northern Hemisphere with respect to the reanalyses throughout the stratosphere.In the wintertime antarctic region the mid-low stratospheric horizontal mixing term in WACCM does not agree with the reanalyses: it shows near-zero positive values, while all the reanalyses show a consistent negative contribution. This disagreement between WACCM and the reanalyses is located in the region and period of the polar vortex development, and can be related to a different representation of the polar jet. In this region the reanalyses are nevertheless affected by large uncertanties of the TEM analysis: the residual term of the budget has the same magnitude as the horizontal mixing term.Even though the residual term can be interpreted as the effect of sub-grid mixing processes, caution must be exerted when considering these regions because the N2O TEM budget is not completetely closed.
The mid-stratospheric arctic region are characterized by smaller uncertanties of the TEM budget together with large differences among the datasets during winter: the WACCM realizations, characterized by a large internal variability, show a smaller horizontal mixing contribution with respect to the reanalyses.
The agreement among datasets is generally improved when considering the middle and low latitudes, especially in the Northern Hemisphere: those regions are characterized by smaller differences among datasets and a well-closed TEM budget.
The inter-annual variability of the horizontal mixing term and the vertical advection term is highly latitude-dependent: the horizontal mixing term presents a large variability, together with a large dataset spread, in the antarctic region in the austral fall and during boreal winter in the Arctic; the vertical advection shows large variability in the arctic region and large model spread in the Tropical regions.

How to cite: Minganti, D., Chabrillat, S., Christophe, Y., Errrera, Q., Abalos, M., Prignon, M., Kinnison, D., and Mahieu, E.: N2O-based climatology of the Brewer-Dobson Circulation in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7432, https://doi.org/10.5194/egusphere-egu2020-7432, 2020.

The intraseasonal (20-90 day) variability of the tropical upper troposphere/lower stratosphere (UTLS)  is dominated by the Madden-Julian Oscillation (MJO). Previous studies showed a strong connection between the MJO and variability in the UTLS circulation and trace gases. However, seasonality of UTLS circulation and trace gas response to the MJO has received very little attention in the literature. In this study, we use observations of trace gases (ozone, carbon monoxide and water vapor) and temperature from the Microwave Limb Sounder (MLS, version 4) and meteorological fields from the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalyses to examine and explain the seasonal and zonal differences in the UTLS temperature, circulation, and trace gas anomalies associated with the MJO propagation. We find that the response of the UTLS during boreal summer months (June -September, JJAS) is different from the response during boreal winter months (November -February, NDJF). Ozone, temperature and circulation anomalies during JJAS are more zonally symmetric with a stronger Kelvin wave response than during NDJF. These differences are explained in terms of seasonal variations in vertically propagating Kelvin waves that strongly depend on the zonal structure of the climatological zonal winds. The trace gas response to the MJO is in agreement with circulation anomalies, showing strong seasonal differences. The analysis of MLS observations presented in this study may be useful for evaluation and validation of the MJO-related physical and dynamical processes in a hierarchy of models.

How to cite: Tweedy, O., Oman, L., and Waugh, D.: The seasonal and zonal differences in the temperature, circulation and composition of the tropical upper troposphere and lower stratosphere due to the MJO, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10418, https://doi.org/10.5194/egusphere-egu2020-10418, 2020.

Midwinter sudden stratospheric warmings (SSWs), characterised by the reversal of the temperature gradient poleward of 60°N and the 10 hPa climatological zonal mean wind from westerly to easterly at 60°N, are known to have pronounced impacts on tropospheric circulation which lead to regional changes in temperature, precipitation and other meteorological variables. Such abrupt events are furthermore known to be associated with large-scale changes in the distribution of stratospheric chemistry constituents, such as ozone (O₃) and water vapour (H₂O), although the implications for stratosphere-troposphere exchange (STE) have not been previously investigated. The evolution of O₃ and H₂O anomalies during an SSW life cycle are first examined from the surface up to 1 hPa using specified-dynamics simulations from the European Centre for Medium-Range Weather Forecasts – Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model over the period 1979-2013. We show that significant positive anomalies in O₃ occur around the onset of an SSW in the middle to lower stratosphere, with persistence timescales of around 50 days in the upper troposphere-lower stratosphere (UTLS). Similarly, we find significant H₂O anomalies in the lowermost stratosphere (± 25 %) for up to 75 days. The extent and magnitude of the anomalies are largely confirmed in both Copernicus Atmospheric Monitoring Service (CAMS) reanalysis and ozonesonde measurements at five different Arctic stations. These chemical perturbations result in local temperature changes of up to 2 K, which may impact numerical weather prediction (NWP) of the tropospheric response to SSWs. Evaluation of the vertical residual velocity (w*) support the notion of transport changes being the driver of the temporal evolution of the anomalies. Using a stratospheric-tagged O₃ tracer, a signal for enhanced STE of ozone is subsequently inferred (~ 5-10 %), which is maximised around 50 days after the SSW onset date. We furthermore attempt to elucidate STE transport pathways using a tropopause fold identification algorithm applied to ERA-Interim during this period, and assess such changes in folding frequency and distribution during such events. Our results highlight that SSWs can induce significantly disturbed O₃ and H₂O distributions in the UTLS, leading to enhanced STE of O₃, with potentially significant implications for radiative fluxes, atmospheric heating rates and air quality.

How to cite: Williams, R., Hegglin, M., Jöckel, P., Garny, H., Shine, K., and Sprenger, M.: The impact of sudden stratospheric warmings (SSWs) on UTLS composition, local radiative effects and air quality, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3545, https://doi.org/10.5194/egusphere-egu2020-3545, 2020.

The extreme disruptions of the wintertime stratospheric circulation during sudden stratospheric warmings (SSW) have important effects on tracer concentrations through alterations in transport and mixing properties. In this presentation we will examine the dynamics that control changes of Arctic ozone during the life cycle of SSWs, providing a quantitative analysis of both advective transport and mixing of Arctic ozone. We use output from four ensemble members (60 years each) of the Whole Atmospheric Community Climate Model, and also use reanalysis and satellite data for validation purposes. The composite evolution of ozone displays positive mixing ratio anomalies up to 0.5 – 0.6 ppmv above 550 K (∼50 hPa) around the central warming date and negative anomalies below (-0.2 to -0.3 ppmv), consistently in observations, reanalysis and model.

Our analysis shows a clear temporal offset between ozone eddy transport and diffusive ozone fluxes. The initial changes in ozone are mainly driven by isentropic eddy fluxes linked to enhanced wave drag responsible for the SSW. The recovery of climatological values in the aftermath of SSWs is slower in the lower than in the upper stratosphere, and is driven by the competing effects of cross-isentropic motions (which work towards the recovery) and isentropic mixing (which delays the recovery). These features are enhanced in strength and duration during sufficiently deep SSWs, particularly those also labeled as Polar-night Jet Oscillation (PJO) events. It is found that SSW-induced ozone concentration anomalies below 600 K (∼40 hPa), as well as total column estimates, persist around one month longer in PJO than in non-PJO warmings.

How to cite: de la Camara, A., Abalos, M., Hitchcock, P., Calvo, N., and Garcia, R.: Enhanced transport and mixing of Arctic ozone during SSWs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5899, https://doi.org/10.5194/egusphere-egu2020-5899, 2020.

We study fast transport of air from the surface into the North American upper troposphere-lower stratosphere (UTLS) during northern summer with a large ensemble of Boundary Impulse Response (BIR) idealized tracers. Specifically, we implement 90 pulse tracers at the Northern Hemisphere surface and release them during July and August months in the fully coupled Whole Atmosphere Community Climate Model (WACCM) version 5. We focus on the most efficient transport cases above southern U.S. (10°-40°N, 60°-140°W) at 100 hPa with modal ages fall below 10th percentile. We examine transport-related terms, including resolved dynamics computed inside model transport scheme and parameterized processes (vertical diffusion and convective parameterization), to pin down the dominant dynamical mechanism. Our results show during the fastest transport, air parcels enter ULTS directly above the Gulf of Mexico. The budget analysis indicates that strong deep convection over the Gulf of Mexico fast uplift the tracer into 200 hPa, and then is vertically advected into 100 hPa and circulated by the enhanced large-scale anticyclone. 

How to cite: Wang, X., Randel, W., and Wu, Y.: Transport into the upper troposphere-lower stratosphere over North America , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-609, https://doi.org/10.5194/egusphere-egu2020-609, 2020.

The lowermost stratosphere (LMS) plays an important role in determining the Earth's energy budget. The chemical species that absorb and re-emit radiation in the LMS have a large spatial and temporal variability, which is controlled by mixing and transport processes. The troposphere and middle stratosphere affect the LMS through large scale isentropic transport across the tropopause or downwelling from higher altitudes.

The data presented in this study originates from two HALO measurement campaigns that allow an interhemispheric comparison of the composition of the lower stratosphere: First the WISE campaign which took place in September and October 2017 over Europe and the North Atlantic, and second the mission SouthTRAC (September and November 2019) where measurements focused on South America and the region around the Antarctic Peninsula.

We use high resolution in-situ measurements of different trace gases (N₂O, O₃, CO₂, CO, SF₆) in order to quantify transport time scales, to estimate tracer fluxes and to examine the prevalent transport pathways. Particularly correlations of trace gases of different lifetime can provide insight in the origin of air masses in the lower stratosphere and their transport histories.

During WISE a remarkable change of the N₂O-O₃ correlation at the 380 K potential temperature isentrope indicates a surprisingly strong distinction between the lowermost stratosphere and the stratosphere, suggesting two mixing regimes. Above 380 K, isentropic mixing occurs between stratospheric air masses from the tropics towards high latitudes leading to a slope flattening effect. In the lowermost stratosphere isentropic mixing connects the stratosphere with the tropical tropopause layer (TTL). Based on CO observations we quantify the contribution of air from the TTL to reach 60 % - 80 % in the LMS. Using CO₂ measurements we estimate a typical time scale of less than 30 days for transport from the TTL into the LMS.

These methods are applied to the observations during SouthTRAC as well. Preliminary CO budget calculations suggest a smaller contribution of TTL air to the LMS in the order of 50 %. This analysis along with correlation slope studies allow for an interhemispheric and interseasonal comparison of the transport processes that were observed during the two measurement periods.

How to cite: Bense, V., Hoor, P., Kluschat, B., Bozem, H., Kunkel, D., Lachnitt, H.-C., Kaluza, T., Joppe, P., Büttner, M., Krause, J., Engel, A., Zahn, A., Grooß, J.-U., Riese, M., Rapp, M., and Sinnhuber, B.-M.: Transport processes in the lowermost stratosphere - interhemispheric differences from trace gas observations during WISE and SouthTRAC, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18936, https://doi.org/10.5194/egusphere-egu2020-18936, 2020.

Water vapor is one of the most important greenhouse gases in the Earth’s atmosphere. Due to the high sensitivity of atmospheric radiative forcing to changes in greenhouse gases in the cold upper troposphere and lower stratosphere (UTLS) region, even small variations in water vapor in the lower LS are an important source of the decadal variability of the surface temperature. This implies the need for a detailed understanding of the observed water vapor variability in the UTLS and their underlying processes.

Isentropic transport of water vapor due to planetary waves and their breaking provides a mechanism for bringing moist tropical tropospheric air into the dry lower extra-tropical stratosphere (exLS, see e.g. McIntyre and Palmer, 1983). Uplifted moist air masses by the Asian and American monsoons at the sub-tropical jet generate maximum water vapor concentrations in the summer/fall season. This water vapor maximum coincides with a maximum in planetary wave breaking in the northern hemisphere lower stratosphere and thus subsequent horizontal poleward transport. This transport serves as the dominant pathway to moisten the exLS in boreal summer (e.g. Ploeger et al., 2013 , Rolf et al. 2018).

We investigate this transport pathway with measurements to better understand the water vapor distribution and their annual cycle in the exLS. Here, we use in-situ measurements of water vapor obtained with the FISH instrument (Fast In-situ Stratospheric Hygrometer) during the aircraft field campaigns TACTS in August/ September 2012 and WISE in September/October 2017. Water vapor observations with the AURA MLS satellite instrument encompassing the entire exLS are used to put the temporal and spatial limited in-situ observations into a larger perspective. A very good agreement between the median of the in-situ water vapor distribution and the satellite observation is found, which shows that the in-situ observations are representative for the water vapor distribution of the exLS. Isentropic transport is shown to be dependent on the planetary wave activity by using the divergence of the Eliassen-Palm flux. Together with an extensive backward trajectory analysis we show that the isentropic transport is the dominant pathway of moistening the exLS up to 420 K potential temperature.

References

• McIntyre, M. E., and T. N. Palmer (1983), Breaking planetary waves in the stratosphere, Nature, 305, 593-600.

• Ploeger, F., Günther, G., Konopka, P., Fueglistaler, S., Müller, R., Hoppe, C., Kunz, A., Spang, R., Grooß, J.‐U., and Riese, M. ( 2013), Horizontal water vapor transport in the lower stratosphere from subtropics to high latitudes during boreal summer, J. Geophys. Res. Atmos., 118, 8111– 8127, doi:.

• Rolf, C., Vogel, B., Hoor, P., Afchine, A., Günther, G., Krämer, M., Müller, R., Müller, S., Spelten, N., and Riese, M.: Water vapor increase in the lower stratosphere of the Northern Hemisphere due to the Asian monsoon anticyclone observed during the TACTS/ESMVal campaigns, Atmos. Chem. Phys., 18, 2973–2983, https://doi.org/10.5194/acp-18-2973-2018, 2018.

How to cite: Rolf, C., Plöger, F., Krämer, M., and Riese, M.: Isentropic transport of water vapor into the extra-tropical lower stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13251, https://doi.org/10.5194/egusphere-egu2020-13251, 2020.

The Brewer-Dobson circulation is the mean meridional circulation in the stratosphere. It is important for the chemical distribution of trace gases in the stratosphere and its thermal structure. Chemistry climate models consistently project an acceleration of its shallow branch in response to increasing greenhouse gas concentrations, while changes in the deep branch have been much less explored. Most models agree that enhanced resolved wave forcing is the main driver of the trend in tropical upwelling in the lower stratosphere although the ultimate mechanism is not well understood. Both changes in wave generation and wave dissipation related to climate change can lead to increased wave driving and modeling results are not conclusive.

Here, we revisit this issue based on the timescales of the BDC response to an abrupt quadrupling of CO2 concentrations. We analyze CMIP5 and CMIP6 preindustrial, 4xCO2 and AMIP simulations of the Whole Atmosphere Community Climate Model (WACCM) to compare the fast and slow responses of the BDC to the increase in CO2. While the fast response is associated with the direct radiative forcing of increasing CO2, the slow response of the BDC is related to warmer sea surface temperatures. Our results show that the shallow branch is tightly coupled to the evolution of tropical surface temperature. About half of the response to an abrupt 4xCO2 increase occurs in the first 10 years in WACCM. In the deep branch, about half of the response of the tropical upwelling in the deep branch is due to warmer SSTs, the other half is radiatively-driven. The waves involved in driving these changes are also investigated together with possible mechanisms.

How to cite: Calvo, N., Marsh, D. R., Garcia, R. R., Chiodo, G., and Polvani, L.: The response of the Brewer Dobson circulation to a quadruple CO2 increase in WACCM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20658, https://doi.org/10.5194/egusphere-egu2020-20658, 2020.

Accurate representation of tracer transport --- the movement of trace constituents by the atmospheric flow --- continues to be a challenge for climate models. Differences in the resolved circulation, biases due to physical parameterizations, and differences in the numerical representation of trace gases result in large variations in transport, even among state-of-the-art climate models. These differences result in disagreement among model projections of the evolution of stratospheric ozone throughout the 21st century particularly in the recovery of the Antarctic ozone hole. In addition to transport, the delicate momentum balance in the upper-troposphere and lower-stratosphere (UTLS) also presents a stiff challenge for model numerics, exposing the impacts of numerical dissipation, the resolution of waves, and the consequences of imperfect momentum conservation. Biases in this region impact the global circulation, e.g., influencing the extratropics jets and stratospheric polar vortices, and alter the transport and exchange of trace gases between and through the troposphere and stratosphere.

In this study, we compare 2 modern dynamical cores (dycores) that employ very different numerics: the cubed sphere finite volume (CSFV) core from GFDL and the spectral element (SE) core from NCAR-CAM5. We force these dycores using identical Held-Suarez diabatic forcing in the troposphere and Polvani-Kushner diabatic forcing in the stratosphere, varying the horizontal and vertical resolution. We observe significant differences in circulation, between the two models at high vertical resolution in the lower and middle tropical stratosphere. While the finite volume core is relatively insensitive to any changes in vertical resolution, the PS and SE dycores resolve considerably different tropical stratospheric dynamics at high vertical resolution (80 levels). These models develop QBO-like westerly winds in the tropics and induce a secondary meridional circulation in the tropical stratosphere, which sets of transport between the models. Using the theoretical leaky pipe transport model we analyze and separate out the transport differences due to differences is diabatic circulation and isentropic mixing and infer that this secondary circulation strikingly modulates stratospheric tracer transport (age of air) by altering the tropical-extratropical mixing, and impacts the extratropical circulation through the subtropical jets. Implications for comprehensive atmospheric modeling are discussed.

How to cite: Gupta, A., Gerber, E., and Lauritzen, P.: Assessing numerical impacts on stratospheric dynamics and transport using the age of air and the leaky pipe theoretical model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4281, https://doi.org/10.5194/egusphere-egu2020-4281, 2020.

The tropical tropopause layer (TTL) provides a major pathway for troposphere-to-stratosphere transport of radiatively active gases, thus it is an important region for understanding stratospheric composition and related climate variability. This work examines the thermal characteristics of the TTL in climate models using the results from state-of-the-art models participated in phase 1 of the Chemistry-Climate Model Initiative (CCMI).
 The CCMI models reproduce reasonable thermal structures in the TTL on climatological and seasonal timescales. However, a near-tropopause temperature bias and corresponding stratospheric moisture bias appear in many models. The temperature bias presents a strong relationship with the ozone bias in the TTL, which causes the temperature bias through local radiative processes. The CCMI models show large inter-model differences in ozone, and it is likely due to different ozone transport mechanisms in the models. These uncertainties could pose a significant limitation on understanding the Earth’s radiation budget and corresponding climate projection. 

How to cite: Kim, J.: Thermal characteristics of the tropical tropopause layer and their implication on stratospheric moisture in CCMI models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4410, https://doi.org/10.5194/egusphere-egu2020-4410, 2020.

Matsuno-Gill circulations arising from tropospheric heating have been widely studied in tropical meteorology, but their impact on stratospheric chemistry and composition has seldom been explicitly evaluated. We show how anticyclonic Rossby wave gyres that form near the tropopause due to equatorially-symmetric Matsuno-Gill heating in near-equinox months provide a mechanism to influence chemistry in the tropical and subtropical upper-troposphere/lower-stratosphere (UTLS). This heating both generates anticyclonic flow in the lower stratosphere, which entrains extratropical air from higher latitudes deeper into the tropics of both hemispheres, and induces cooling in this already cold region. These two aspects of the circulation combine to allow heterogeneous chlorine activation on the surface of sulfuric acid aerosols to proceed rapidly. We use reanalysis to show that these Matsuno-Gill heating and wind response patterns are present in the months of interest, and then demonstrate that, in the WACCM model, they can substantially influence the distributions of species related to chlorine activation such as ClO and NO₂. This provides a potential target for future tropical UTLS observation campaigns, and demonstrates a previously unrecognized mechanism in near-equinox months for dynamical influences on the spatial structures of atmospheric composition changes in this region. 

How to cite: Wilka, C., Solomon, S., Cronin, T., Kinnison, D., and Garcia, R.: New Connections Between Tropical Dynamics and Lower Stratospheric Chemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12615, https://doi.org/10.5194/egusphere-egu2020-12615, 2020.

It is well established that ozone-depleting substances (ODS) have been the primary cause of stratospheric ozone depletion. It is also widely accepted that stratospheric ozone depletion has been the primary driver of summertime circulation trends in the Austral Hemisphere in the second half of the twentieth century. However, the climate impacts of ODS that are independent of ozone depletion have received little attention. It has long been known that, while much less abundant than carbon dioxide, ODS have a much higher global warming potential (GWP) ecent studies have indicated that ODS may have played a key-role in the observed weakening trends of the Walker circulation (Polvani and Bellomo, 2019), and in the warming of the Arctic and the associated sea ice loss (Polvani et al., 2020). that the climate efficacy of ODS may be much larger than previously thought, but .

Here, we seek to better understand the radiative effect of ODS in the global atmosphere. Instead of confining our attention on a single metric, e.g. globally averaged radiative forcing (RF) or GWP which are typically reported in the IPCC Assessment Reports, we seek to understand how ODS alter the temperature structure of the entire atmosphere. Focusing on the half-century 1950-2000, which saw the largest growth of ODS concentrations in the atmosphere, we start by performing careful computations of the RF of individual ODS, including the effects of rapid temperature adjustments. We then explore how the vertical and latitudinal distribution of ODS (which are not well mixed in the stratosphere) affects their RF, and what temperature responses are associated with those changes. These calculations are repeated individually for each of the other well-mixed GHG, as well as for other composition changes arising from ODS (ozone depletion). It is shown that ODS, in contrast to other GHG, warm the lower stratosphere, implying a different fingerprint from CO2. Furthermore, the RF of ODS exhibits the largest meridional gradient of any other well-mixed GHG. Implications for the climate efficacy of ODS, and more generally for climate sensitivity, will be discussed.

References

Polvani, L.M and K. Bellomo: The key role of ozone depleting substances in weakening the Walker circulation in the second half of the 20th century, J. Climate, 32, 1411-1418 (2019).

Polvani et al.,: Substantial twentieth-century Arctic warmng caused by ozone depleting substances, Nature Climate Change, in press (2019)

How to cite: Chiodo, G. and Polvani, L. M.: Shedding new light on the radiative impacts of ozone-depleting substances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4687, https://doi.org/10.5194/egusphere-egu2020-4687, 2020.

Ozone in the upper troposphere is a dominant radiative constituent.  In this study, we investigate ozone variability due to stratospheric intrusions in the upper troposphere over India, and its associated radiative impacts during monsoon breaks co-occurring with El Niño. For this purpose, we use the ECHAM5-HAMMOZ, Global-Chemistry-climate model simulations, and ERA-Interim reanalysis data. Our analysis shows that during El Niño deep stratospheric intrusions, occurring at the North India - Tibetan Plateau (NI-TP) region and the western edge of the monsoon anticyclone, lead to an enormous increase in ozone amounts (~160 ppb) in the upper troposphere over India. These intrusions elevate the surface ozone levels by ~20 ppb and ozone radiative forcing by ~0.33 W m^-2 at the top of the atmosphere (TOA). 

Interestingly, the stratospheric intrusions are associated with a wave train composed of cyclonic and anticyclonic circulation in the upper troposphere, emanating from El-Niño region in the east Pacific, traversing towards NI-TP locale. The wave train transports extra-tropical cold air mass, producing an anomalous cooling of ~2 - 3 K in the upper troposphere over NI-TP. The cold wave train induces Rossby wave breaking (RWB), which facilitates stratospheric intrusions, thereby enhancing subsidence over NI-TP region. Additionally, this severe cold subsidence over North India during break days may further intensify the deficit rainfall condition during break days.

How to cite: Roy, C., Fadnavis, S., and Thazhe Purayil, S.: The stratospheric ozone rich cold intrusion during El-Nino over the Indian region: implication during the Indian summer monsoon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-937, https://doi.org/10.5194/egusphere-egu2020-937, 2020.

The water vapour in the stratosphere is a strong green-house gas. The usual picture makes its abundance depend first on the temperature of the tropical tropopause via saturation, and second on the activity of the scarce but intense troposphere-stratosphere transport by the very deep convection. This study, designed to identify the various processes at play at the regional scale, benefits from the insitu observations during the StratoClim campaign (August 2017) and the 100-m vertical resolution of a cloud-resolving simulation over the whole south Asia (key region for the stratospheric water budget during the boreal summer). With a combination of Eulerian budget and Lagrangian track of the air masses, we show how the three main driving processes compete: the convective injections via overshoots, the turbulent diffusion, and the freeze-drying episodes driven by large-scale gravity waves, and how much they contribute to the stratospheric humidity at different altitudes.

How to cite: Dauhut, T., Lee, K.-O., Chaboureau, J.-P., Noël, V., and Haynes, P.: The processes driving the water budget in the tropical stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8666, https://doi.org/10.5194/egusphere-egu2020-8666, 2020.

We've  built a numerical model of the propagation and scattering of laser radiation in a turbulent medium, taking into account molecular and aerosol scattering . The model will be based on the method of random phase screens. In the framework of this method, the direct propagation of laser radiation is modeled by the method of stepwise splitting. For this purpose, a random medium is divided into layers, and each layer is presented as a composition of an infinitely thin phase screen and vacuum propagation. To simulate a random medium, random phase screens whose phase thickness is associated with the spectrum of random medium inhomogeneities will be used.

Modeling incoherent (molecular and aerosol) scattering is based on the principle of reciprocity. Since the Green function for the propagation problem in a random medium is symmetric with respect to the permutation of the source and receiver, the backscattering problem can be reduced to solving the direct radiation propagation problem. In this case, the summation of the contributions of elementary random scatterers are performed in an incoherent manner. 

         In 2009–2015, with the support of the Commission of the European Communities, as part of the 7th framework program, the DELICAT project  (DEmonstration of LIdar based Clear Air Turbulence detection) was carried out . In the course of this project , a lidar was designed , manufactured and tested for installation on an airplane with the aim of early detection of clear sky turbulence . The emitted signal was polarized vertically. The scattered radiation was measured in two polarizations: vertical and horizontal. The experiment showed that the effects of aerosol scattering at given altitudes can almost never be neglected.

    To build an aerosol scattering model, the experimental data from the DELICAT project was analyzed . Spectral and cross-spectral analysis of measurements in two polarizations is already  performed. Cross-spectral analysis will evaluate the effects of radiation depolarization. A model of the aerosol scattering matrix describing the observed effects of depolarization was constructed. In particular, multicomponent models will be considered. The spatio-temporal properties of aerosol clouds are closely investigated and also  contribution of variations in the measurement geometry during the flight to measurement errors.

       The constructed numerical model shall make it possible to plan similar experiments in the future and better understand the role of aerosol and molecular scattering in the interpretation of experimental data in order to detect clear sky turbulence.

This work was supported by the RFBR grant No. 18-35-00368

How to cite: Mamontov, A., Koval, O., and Kulikov, V.: Development of numerical model of laser sensing of clear air turbulence (CAT) taking into account effects of the propagation of laser radiation in a random medium, molecular and aerosol scattering, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-365, https://doi.org/10.5194/egusphere-egu2020-365, 2020.

In the atmosphere, internal gravity waves (GWs) are a naturally occurring and ubiquitous, though intermittent phenomenon. In addition, GWs (especially orographic; OGWs) are asymmetrically distributed around the globe. In current generation global climate models (GCMs), GWs are usually smaller than the model grid resolution and the majority of their spectrum therefore must be parameterized. To some extent, the intermittency and asymmetry of a spatial distribution of the resulting OGW drag (OGWD) is present also in GCMs. As the GW parameterization schemes in GCMs are usually tuned to get the zonal mean climatology of particular features right, an important question emerges: what kind of influence do GW parameterizations have on the individual models atmosphere locally? Here we focus on answering this question regarding the impact of spatiotemporally intermittent OGW forcing in the extra-tropical lower stratosphere region (LS). The LS region is characterized by a strong interplay of chemical, physical and dynamical processes. To date, the representation of this dynamically active region in models frequently mismatches observations. Although we can find a climatological maximum of oGWD in the LS, the role of OGW forcing for the transport and composition in this region is poorly understood. We combine observational evidence, idealized modeling and statistical analysis of GCM outputs to study both the short-term and long-term model response to the OGW forcing. The results presented will question the relationship between the advective part of the Brewer- Dobson circulation and the zonally asymmetric GW forcing, and a so-far neglected link between oGWD and large-scale quasi-isentropic stirring will be discussed.

How to cite: Rieder, H., Šácha, P., Eichinger, R., Kuchař, A., Samtleben, N., Pišoft, P., and Jacobi, C.: A different perspective on how parameterized orographic gravity waves influence atmospheric transport and dynamics in current generation global climate models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4171, https://doi.org/10.5194/egusphere-egu2020-4171, 2020.

The upper troposphere / lower stratosphere (UTLS) region has been identified as a region with a high climate sensitivity of the Earth's atmosphere. Past studies have shown that mixing processes can have a substantial impact on the radiative budget of the atmosphere with implications for the climate of the planet. However, in most large-scale models some of these mixing processes are hardly resolved or considered explicitely.
In this study, we focus on clear air turbulence (CAT) as a dynamically driven mixing process, which can induce vertical mixing of radiative active trace gases. For this purpose, we have equipped a chemistry-climate model with a diagnostics for dynamical CAT including vertical stability conditions and a mixing parameterisation for CAT-induced vertical exchange of trace gases.  
With the help of this tool we analyse the occurrence of CAT, the mixing of chemical compounds and the resulting radiative impact of this mixing.
The model simulations indicate a more efficient mixing of trace species in the UTLS, weakening some of the strong gradients of compounds, such that an occasional deeper penetration into the lower stratosphere becomes possible.
A suitable choice of simulation configuration also allows us to disentangle the radiative forcing of climate active gases (e.g., N₂O, O₃, CH₄) from
feedback processes occurring in the holistic system. 

How to cite: Tost, H. and Hoor, P.: Climate impact of clear air turbulence induced mixing in the UTLS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7289, https://doi.org/10.5194/egusphere-egu2020-7289, 2020.

The tropopause acts as a transport barrier between the upper troposphere and the lower stratosphere. Non-conservative (i.e. PV changing) processes are required to overcome this barrier. Orographically generated gravity waves (i.e. mountain waves) can potentially lead to cross-isentropic fluxes of trace gases via the generation of turbulence. Thus they may alter the isentropic gradient of these trace species across the tropopause.
The specific goal of this study is to identify cross-isentropic mixing processes at the tropopause based on the distribution of trace gases (i.e. tracer-tracer correlations). Based on airborne in-situ trace gas measurements of CO and N₂O during the DEEPWAVE (Deep Propagating Gravity Wave Experiment) campaign in July 2014 we identified mixing regions above the Southern Alps during periods of gravity wave activity. These in-situ data show that the composition of the air above the Southern Alps change from the upstream to the leeward side of the mountains indicating cross isentropic mixing of trace gases in the region of gravity wave activity.
We complement our analysis of the measurement data with high resolution operational analysis data from the ECMWF (European Centre for Medium-Range Weather Forecasts). Furthermore, using potential vorticity and stability parameters.
Using 3D wind fields, data form Graphical Turbulence Guidance (GTG) system and in-situ measurements of the vertical wind we identify occurrence of turbulence in the region of mixing events. Using wavelet analysis, we could identify the spatial and temporal scales of local trace gas fluxes. We also give estimates of cross-isentropic flux, i.e. we want to quantify the mixing in terms of exchange.

How to cite: Lachnitt, H.-C., Hoor, P., Kunkel, D., Hofmann, S., Bramberger, M., Rapp, M., Dörnbrack, A., and Schlager, H.: Cross-isentropic mixing: A DEEPWAVE case study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9544, https://doi.org/10.5194/egusphere-egu2020-9544, 2020.

The extratropical transition or mixing layer indicates the chemical transition from well mixed troposphere to the stably stratified stratosphere . It is located around the classical defitinition of the tropopause and is defined by a set of unique tracer-tracer correlations. Physically, it is the result of cross-tropopause transport, however, many processes associated with the formation and maintenance of the extratropical transition layer with its very distinct features as well as the importance of its overlap with the tropopause inversion layer (TIL) are still a subject of research. In particular, turbulent motions in the UTLS and their relative importance for the ExTL are still unknown.

We analyse the top end of the spectrum of vertical shear of the horizontal wind, S², in the troposphere and stratosphere as a proxy for turbulent motions. For this we use 10 years of ECMWF (European Centre for Medium-Range Weather Forecasts) ERA5 reanalysis data. We focus our analysis on the Northern Hemisphere extratropical UTLS, and more specifically on the Northern Pacific and Atlantic sectors. We find strong signatures of high S² just above the tropopause in both region. However, differences between the two regions are evident due to difference in the jet stream characteristics in these two regions . The areas of strong vertical wind gradients appear as regions of reduced Richardson numbers in the elsewhere highly dynamically stable lowermost stratosphere. We compare features of these regions in the model output with known characteristics of the extratropical transition layer to see if they are linked.

This work was supported by DFG grant no. KU 3524/1-1.

How to cite: Kaluza, T., Kunkel, D., and Hoor, P.: On the accumulation of enhanced vertical shear of the horizontal wind in the upper troposphere / lower stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10891, https://doi.org/10.5194/egusphere-egu2020-10891, 2020.

Over the course of the summer, when the subtropical jet is weakest, quasi-isentropic transport of young air from the troposphere and the tropical tropopause layer into the northern hemisphere (NH) lowermost stratosphere (LMS) is increased resulting in a drastic change of LMS chemical composition between spring and fall. The focus of this work is on the role of different transport paths into the NH LMS, including outflow from the Asian Monsoon, and their associated time scales of transport and mixing.

We present and analyse in situ measurements of CO₂ and various long-lived tracers obtained during three recent aircraft campaigns encompassing over 40 research flights in the NH UTLS during winter/spring, summer, and fall. The POLSTRACC/GW-LCYCLE/SALSA campaign probed the northern high latitude LMS in winter/spring 2016, deploying the German research aircraft HALO from Kiruna (Sweden) and from Germany. The second campaign deployed the M55 Geophysica research aircraft in July/August 2017 from Kathmandu, Nepal, in the frame of the EU-funded project StratoClim (Stratospheric and upper tropospheric processes for better Climate predications) in order to probe in situ for the first time the inside of the Asian Monsoon anticyclone. Roughly two months later the WISE (Wave-driven ISentropic Exchange) campaign deployed again HALO from Shannon (Ireland) in September and October 2017 to investigate isentropic transport and mixing in the NH LMS.

The University of Wuppertal measured CO₂ and a suite of long-lived tracers on each aircraft. On the Geophysica, the measurements were made with the HAGAR (High Altitude Gas AnalyzeR) instrument. On HALO, a recently developed extended 5-channel version, HAGAR-V, was flown, which in addition measured a suite of short-lived tracers by GC coupled with a mass spectrometer. The University of Mainz measured N2O and CO on HALO using laser absorption techniques. For our analysis we use mixing ratios of CO₂, SF₆, CFC-11, CFC-12, and N₂O.

Owing to their different lifetimes, tropospheric growth (for SF₆) and a seasonal cycle (for CO₂), the LMS distributions of these long-lived trace gases and their development between spring and fall contain key information about the origin and mean stratospheric age of LMS air as well as time scales of rapid isentropic transport and mixing. The analysis of tracer measurements is complemented by simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) providing information on age of air spectra and fractions of origin from specific surface regions, allowing in particular to assess the role of the Asian Monsoon in determining the composition of the NH LMS in fall.

How to cite: Rau, A., Lauther, V., Wintel, J., Gehardt, E., Hoor, P., Krause, J., Kluschat, B., Plöger, F., Vogel, B., and Volk, M.: Investigation of transport in the northern lowermost stratosphere between spring and fall using airborne in situ tracer measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21312, https://doi.org/10.5194/egusphere-egu2020-21312, 2020.

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an imaging Fourier transform spectrometer (iFTS) using a 2-dimensional detector array to record emission spectra in the mid-infrared region with high spatial resolution. GLORIA is operated on high altitude research aircraft, mainly in the limb observational geometry to measure vertical profiles of temperature and atmospheric trace species with high vertical resolution.

In autumn 2017, the Wave-driven ISentropic Exchange (WISE) aircraft campaign took place from Shannon (Ireland). Sixteen flights with the High Altitude and Long Range Research Aircraft (HALO) were performed between 31 August and 21 October 2017 over the eastern North Atlantic region.

GLORIA observations were analysed with regard to pollutant species like C₂H₆, C₂H₂, HCOOH, and PAN, which are produced at distinct source regions near the ground and transported to remote regions due to their atmospheric lifetime of several weeks. Enhanced volume mixing ratios of these molecules were detected along some parts of the flight track in the upper troposphere and lowermost stratosphere (UTLS).

Measured profiles of these species are compared to simulations from the ECHAM/MESSy Atmospheric Chemistry (EMAC) model and reanalysis data from the Copernicus Atmosphere Monitoring Service (CAMS). Furthermore, emission tracers and back-trajectories from the Chemical Lagrangian Model of the Stratosphere (CLaMS) are used to analyse the source regions of these pollution events.

How to cite: Wetzel, G., Friedl-Vallon, F., Glatthor, N., Grooß, J.-U., Gulde, T., Höpfner, M., Johansson, S., Khosrawi, F., Kirner, O., Kleinert, A., Kretschmer, E., Maucher, G., Nordmeyer, H., Oelhaf, H., Orphal, J., Piesch, C., Sinnhuber, B.-M., Ungermann, J., and Vogel, B.: GLORIA observations of pollution tracers C2H6, C2H2, HCOOH, and PAN in the North Atlantic UTLS region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6931, https://doi.org/10.5194/egusphere-egu2020-6931, 2020.

The increasing future methane (CH₄) leads to changes in the lifetime of CH₄ and in the Hydroxyl radical (OH) and (O₃) mixing ratios and distribution in the lower atmosphere. With increasing CH₄ the lifetime of CH₄ and the O₃ mixing ratios in the troposphere will increase, the tropospheric OH mixing ratios will decrease (Winterstein et al., 2019; Zhao et al., 2019). The CH₄ changes, together with the future Nitrous oxide (N₂O) and temperature increase, will lead to a different tropospheric chemistry. For example, substances as acetone (CH₃COCH₃), ethane (C₂H₆), formic acid (HCOOH) or peroxy acetyl nitrate (PAN) will change their distribution and mixing ratios.

In different studies we could show that EMAC (ECHAM/MESSy Atmospheric Chemistry, Jöckel et al., 2010) has the ability to simulate some of the mentioned tropospheric substances in comparison to results of the GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) instrument, used on board of the research aircrafts Geophysica and HALO during the STRATOCLIM (July/August 2017) and WISE (August to October 2017) campaigns (Johansson et al., 2020; Wetzel et al., 2020).   

In this study, we will additional show the first results of the simulated future changes of tropospheric chemistry (especially with focus on CH₃COCH₃, C₂H₆, HCOOH and PAN and the upper troposphere) related to the future increase of CH₄, N₂O and temperature change as a result of climate change. For these we use different EMAC simulations from the project ESCiMo (Earth System Chemistry Integrated Modelling, Jöckel et al., 2016).

We will present some results of the comparison of EMAC to GLORIA and results with regard to the future development of the (upper) tropospheric chemistry in EMAC.    

How to cite: Kirner, O., Patrick, J., Johansson, S., Wetzel, G., and Winterstein, F.: Simulation of current and future tropospheric chemistry with the Earth System Model EMAC, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21478, https://doi.org/10.5194/egusphere-egu2020-21478, 2020.

Since the end of the 1980's, the Montreal Protocol regulates production and use of chlorine and bromine containing substances because they thin out the ozone layer. This has led to a phase out of the long-lived halocarbons like the chlorofluorocarbons (CFCs). Next to the long-lived halocarbons, bromine and chlorine containing substances with atmospheric lifetimes of less than 6 months can reach the lower stratosphere. These substances, also known as "very short-lived" substances (VSLS), have their origin both from natural and anthropogenic sources. An increase of the relative contribution of the VSLS to the stratospheric halogen loading is assumed. Due to their short lifetime, chlorine and bromine of these gases are released quickly into the stratosphere, making them particularly effective catalysts for destruction of ozone in the lower stratosphere.

Here we present airborne measurements of halocarbons including chlorine and bromine VSL source gases. Measurements were taken on the HALO aircraft during the measurement campaign SOUTHTRAC in the Southern Hemisphere UTLS. Using an airborne GC/MS system in electron impact ionization mode, samples were taken in a time resolution of around 6 minutes. One of the focuses are the exchange processes between the Northern and Southern Hemisphere. We further compare results of this campaign with these of previous ones of the Northern Hemisphere.

How to cite: Jesswein, M., Soria Galvarro, S., Keber, T., Schuck, T., Wagenhäuser, T., and Engel, A.: Observed distribution of halocarbons in the Southern Hemispheric UTLS and implications for the bromine and chlorine budget of the lowermost stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2688, https://doi.org/10.5194/egusphere-egu2020-2688, 2020.

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an imaging Fourier transform spectrometer (iFTS) using a 2-dimensional detector array to record emission spectra in the mid-infrared region with high spatial resolution. GLORIA has been operated on the High Altitude and Long Range Research Aircraft (HALO) during the SouthTRAC campaign in September-November 2019. The campaign with base in Rio Grande (Tierra del Fuego) consisted of two observational periods, mainly in September and November 2019. Apart from many local flights, between the two phases HALO returned to Germany which allowed us to acquire long-range hemispheric cross-sections.

Two dimensional distributions of pollution species like C₂H₆, C₂H₂, HCOOH, and PAN, which are produced as primary and secondary products from biomass burning sources have been derived from the GLORIA observations. We will show that during the hemispheric cross sections as well as during some of the local flights, GLORIA observed pollution plumes with extensions of many kilometres in altitude and hundreds of kilometres horizontally with strongly enhanced concentrations of these species.

Trajectory analysis as well as comparisons to Microwave Limb Sounder (MLS) satellite observations show that the origin of plumes are mainly fires in South America and Africa, but also first signs of the Australian bush fires have been detected in the UTLS as early as November 2019.

How to cite: Friedl-Vallon, F., Ungermann, J., Johansson, S., Wetzel, G., Geldenhuys, M., Engel, A., Grooß, J.-U., Gulde, T., Höpfner, M., Hoor, P., Kleinert, A., Kretschmer, E., Maucher, G., Orphal, J., Piesch, C., Preusse, P., Rapp, M., Riese, M., Santee, M. L., and Sinnhuber, B.-M.: Biomass burning pollution products C2H6, C2H2, HCOOH, and PAN in the Southern hemisphere UTLS region observed by the GLORIA instrument during the SouthTRAC HALO aircraft campaign Sep-Nov 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10351, https://doi.org/10.5194/egusphere-egu2020-10351, 2020.

Water vapor is one of the strongest greenhouse gases of the atmosphere. Its driving role in the upper troposphere / lower stratosphere region (UTLS) for the radiation budget was shown by e.g. Riese et al., (2012). Despite its low abundance of 4 - 6 ppmv in the stratosphere, even small changes in its mixing ratio can leed to a positive feedback to global warming. To better understand changes and variability of water vapor in the lower stratosphere, we focus here on exchange processes from the moist troposphere to the dry stratosphere in the mid latitudes. These processes are caused by extreme vertical convection, which is expected to increase in intensity and frequency with progressive global climate change.

Within the MOSES (Modular Observation Solutions for Earth Systems) campaign in the summer of 2019, two extreme vertical convection events could be captured with balloon borne humidity sensors over the eastern part of Germany. The comparison of measurements before and after both events reveal distinct water vapor enhancements in the lower stratosphere and show that even in mid-latitudes over shooting convection can impact the water vapor mixing ratio in the UTLS. The measurements are compared with the Microwave Limb Sounder (MLS) data as well as ECMWF reanalysis data.

We will show a deeper analysis of both events by using visible and infrared weather satellite images in combination with meteorological fields of ECMWF. Backward trajectories of the air masses with the enriched water vapor mixing ratios calculated with the CLAMS model and combined with the satellite images can confirm the convective origin. Additionally, we show the further development of this distinct water vapor filaments within the lower stratosphere in order to trace the transport and mixing process, based on an analysis of forward trajectories.

How to cite: Khordakova, D., Rolf, C., Krämer, M., and Riese, M.: Direct injection of water vapor into the lower stratosphere through extreme convection: A case study for the summer 2019 in the mid latitudes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14224, https://doi.org/10.5194/egusphere-egu2020-14224, 2020.

Cirrus clouds and their potential formation regions, so-called ice-supersaturated regions (ISSRs) occur frequently in the tropopause region. It is assumed that ISSRs and cirrus clouds can change the tropopause structure by diabatic processes, driven by latent heating due to phase transitions and interaction with radiation. These effects may also alter the distribution of potential vorticity (PV) in the upper troposphere, thus leading to changes in large scale dynamics and stratosphere-to-troposphere exchange.  

The measurement of water vapour at the tropopause level is not trivial. Beside radiosonde data the most important in-situ dataset is provided by in-service passenger airplanes. The European Research Infrastructure ’In-service Aircraft for a Global Observing System’ (IAGOS) (Petzold et al., 2015) provides long-term in-situ measurements on board commercial passenger aircraft. Along its flight track every aircraft is monitoring the chemical composition of the surrounding air and atmospheric state parameters by compact instruments. Especially in the upper troposphere/lowermost stratosphere (UTLS) these measurements are very valuable as most flight tracks are situated in heights between 9 to 13 km, depending on the actual weather conditions, seasons and geographic region. 

However, for many research questions a three-dimensional picture including a sufficient temporal resolution of the water vapour fields in the UTLS region is required. Hence, in our study we use the in-situ data from IAGOS to quantify the quality of the established and often used ERA-Interim data set. The underlying IFS-model of this reanalysis data allows explicitly ice-supersaturation in cloud free conditions and is therefore suitable for comparison. For instance, we compare properties such as the seasonal cycle of the vertical distribution of water vapour mixing ratio, relative humidity and the fraction of ice-supersaturated regions. 

How to cite: Reutter, P., Neis, P., Rohs, S., Sauvage, B., Spichtinger, P., and Petzold, A.: Ice supersaturated regions: properties and validation of ERA-Interim reanalysis with IAGOS in situ water vapor measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9301, https://doi.org/10.5194/egusphere-egu2020-9301, 2020.

During the Asian summer monsoon (ASM) season, the stratosphere-troposphere exchange (STE) process has a significant effect on the stratospheric chemical constituent concentration and spatial distribution. In order to further explain the STE process during the ASM season, the impact of ASMA intensity on chemical species within the anticyclone escaping process during the ASM season is studied. Using the MERRA 2, NCEP reanalysis data and MLS satellite data in June, July and August (JJA) of 2004-2017, the relationship between the day-to-day intensity variation of the ASMA and the horizontal distribution of ozone (O₃) and carbon monoxide (CO) during the intra-seasonal east-west oscillation is discussed based on an ASMA intensity index we defined. The results show that the intensity of the ASMA varied during the intra-seasonal east-west oscillation. The ASMA intensity index increased continuously from early June and peaked during mid-July to early August. ASMA has a constraints effect on the air inside. Its intra-seasonal oscillation and its intensity influenced the chemical distribution in the upper troposphere and lower stratosphere (UTLS). The distribution of chemical substances during its strong periods (SP) were relatively concentrated than that in weaker periods (WP). The air inside of the ASMA was easier to mix into stratosphere when the intensity was weak, and vice verse. The intensity variation of the ASMA caused by its intra-seasonal oscillation may affect the STE process during the Asian summer monsoon season.

How to cite: Luo, J. and Peng, K.: The Iimpact of the Iintraseasonal Intensity Variation of Asian Summer Monsoon Anticyclone on Chemical Constituents Distribution in the Upper Troposphere and Lower Stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3223, https://doi.org/10.5194/egusphere-egu2020-3223, 2020.

A robust but thin aerosol layer in summer extending geographically from Eastern Mediterranean to Western China, the Asian Tropopause Aerosol Layer (ATAL) was observed and verified by the CALIPSO lidar measurements. However, its source and forming mechanism is still under debate. In August 2018 and 2019, two experimental campaigns over the Tibetan Plateau were carried out at Golmud (GLM, 36.48°N, 94.93°E) and Qaidam (QDM, 37.74°N, 95.34°E), during which a balloon-borne Portable Optical Particle Counter (POPS) was used to measure the features of aerosol particulates. The in-situ measurements show a robust ATAL around the tropopause, ranging from 14 to 18 km a.s.l., with a maximum aerosol number density of 35–40 cm^-3 and a maximum aerosol mass concentration of 0.13 μg m^-3 for particles with diameters between 0.12 and 3 μm, and majority of the particulates (98%) are smaller than 0.4 μm in diameter.

Backward-trajectory simulations are conducted with the Massive-Parallel Trajectory Calculations (MPTRAC) model to investigate the possible sources and transport pathways of the observed particulates. The backward-trajectory analysis revealed that the air parcels arrived at the altitude of the ATAL through two separate pathways: 1) the uplift below the 360 K isentropic surface, where air parcels were first elevated to the upper troposphere and then joined the ASM anticyclonic circulation, which will take about 5–10 days; and 2) the quasi-horizontal transport along the anticyclonic circulation, located approximately between the 360 and 440 K isentropic surfaces. The dispersion of the volcanic aerosol from the volcanic eruption of Raikoke in June 2019 has enhanced the aerosol layer in the Tibetan Plateau upper troposphere and lower stratosphere (UTLS), but the ATAL was not concealed by the volcanic plume because the boundary of the Asian summer monsoon (ASM) anticyclone acted as a transport barrier which stopped most of the volcanic aerosol entering the ASM region. Only at most 20% of the aerosol particulates observed in the Tibetan Plateau UTLS was contributed by the Raikoke volcanic eruption. Comparing with the Nabro eruption in 2011, the influence of volcanic eruption on the ATAL significantly depends on the relative geographical location of the volcanic eruption and the ASM anticyclone, as well as the volcanic plume height.

How to cite: Wu, X., Zhang, J., and Lyu, D.: In-situ Measurements of the Tropopause Aerosol Layer at the Tibetan Plateau and the Influence of the Volcanic Eruptions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1346, https://doi.org/10.5194/egusphere-egu2020-1346, 2020.

Transport of air masses from the surface into the atmosphere occurs via a variety of processes (including clear-air turbulence, atmospheric convection and large-scale circulations), which entails a multitude of transport time scales. This complexity can be characterized in an atmospheric transport model by calculating the age of air spectrum (transit time distribution from the surface). Up to now, mainly the slow time scales of stratospheric and interhemispheric transport (>10 days) have thus been studied. Vertical transport through the troposphere, for which convection is the major player, has only been evaluated using a handful of measured compounds (Radon, CO2 and SF6). However, a wealth of chemically relevant species are affected by the detailed structure of the age spectrum. Recent work (Luo et al., 2018) have used this sensitivity in order to gain observational insights into the tropospheric age spectrum, calling for a comparison with models.

To that end, we derive upper tropospheric and tropopause age spectra in the EMAC (ECHAM/MESSy Atmospheric Chemistry) model using the Boundary Impulse Response (BIR) method. Because of the large range of time scales involved in tropospheric transport, which extend from tens of minutes (convective transport) to years (stratospheric intrusions), we rely on a suite of pulses with variable durations providing hourly resolution for short time scales (< 12 hours) and monthly for long ones (> 1 month). We first describe the age spectra obtained and their diurnal and seasonal variability. Then, we examine the transport properties from a few specific surface regions to the upper troposphere and stratosphere, with an emphasis on fast pathways from the tropical Western Pacific and on interhemispheric transport. Finally, we investigate the sensitivity of different transport pathways to changes in some of the available model parameterizations (convection) and to different set-ups (using nudging or not).

How to cite: Podglajen, A., Charlesworth, E., and Ploeger, F.: Global age of air spectrum from the earth surface to the upper troposphere and tropopause: a model study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9907, https://doi.org/10.5194/egusphere-egu2020-9907, 2020.

One of the key questions in the air quality and climate sciences is how will tropospheric ozone concentrations change in the future. This will depend on two factors: changes in stratosphere-to-troposphere transport (STT) and changes in tropospheric chemistry. Here we aim to identify robust changes in STT using simulations from the Chemistry Climate Model Initiative (CCMI) under a common climate change scenario (RCP6.0). We use two idealized stratospheric tracers implemented in the models to examine changes in transport. We find that the strengthening of the shallow branch of the Brewer-Dobson circulation (BDC) in the lower stratosphere and of the upper part of the Hadley cell in the upper troposphere lead to enhanced STT in the subtropics. The acceleration of the deep branch of the BDC in the NH and changes in eddy transport contribute to increase STT at high latitudes. In the SH, the deep branch does not accelerate due to the dynamical effects of the ozone hole recovery.

How to cite: Abalos, M., Orbe, C., Kinnison, D., Plummer, D., Oman, L., Jöckel, P., Morgenstern, O., Garcia, R., Zeng, G., Stone, K., and Dameris, M.: 21st century trends in stratosphere-to-troposphere transport , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2768, https://doi.org/10.5194/egusphere-egu2020-2768, 2020.

Although a general recovery of stratospheric ozone is expected after the successful implementation of the Montreal Protocol, strong indications for a decline in lower stratospheric ozone in the extratropics are still evident. Related studies attribute this decline to internal dynamic variability affecting the UTLS, in particular associated to the QBO and the exchange of air masses between tropical and extratropical regions. The dynamics affect the transport of ozone from the source region in the tropics into the extratropical lower stratosphere. More so, dynamics affect the structure of the lower stratosphere. In particular, the locations of the tropopause and of isentropic surfaces in the lower stratosphere, i.e., the region up to ~25 km altitude, affect the vertical profile of ozone and as such the integrated column ozone in the lower stratosphere.
This study aims to address the relation between the changing altitude of the tropopause and isentropic surfaces in the lower stratosphere and the declining ozone in the extratropical UTLS. For this we use reanalysis data from ECMWF and dynamic linear modeling to study trends of the dynamic tropopause and of the thermodynamical structure and the potential consequences of these trends for lower stratospheric ozone. In particular, we ask the question: do ozone trends still show a decline if we use a dynamic instead of a fixed coordinate system to calculate these trends?

How to cite: Kunkel, D., Weyland, F., Ball, W., and Hoor, P.: Temporal changes in the structure of the UTLS and their potential impact on lower stratospheric ozone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5497, https://doi.org/10.5194/egusphere-egu2020-5497, 2020.

The CARIBIC (Civil  Aircraft  for  the  Regular  Investigation  of the atmosphere Based on an 
Instrumented Container) project is part of the a European research infrastructure IAGOS (In-
Service Aircraft for a Global Observing System) making regular in-situ measurements of more 
than 100 atmospheric constituents, include ozone and water vapour, on-board of an in-service 
passenger  aircraft  operated  by  Lufthansa.  The  dataset  of  the  IAGOS-CARIBIC  is  therefore 
ideally suited as a testbed for the SPARC (Stratosphere-troposphere Processes And their Role 
in Climate) activity OCTAV-UTLS (Observed Composition Trends And Variability in the Upper 
Troposphere and Lower Stratosphere). One key aspect, shown here as work in progress, is to 
develop, define and apply common metrics for the comparison of different UTLS datasets 
using a variety of meteorological coordinate systems derived from reanalysis datasets. The 
focus here is on the variability of ozone in the upper troposphere and lower stratosphere 
(UTLS) on interannual and seasonal timescales and the observed trends. The in-situ ozone 
measurements by IAGOS-CARIBIC are analysed relative to different tropopause definitions 
and coordinate systems. All these meteorological information applied here are produced with 
the JETPAC tool ‒ Jet and Tropopause Products for Analysis and Characterization (Manney et 
al., 2011).

How to cite: Boenisch, H., Zahn, A., and Millan, L.: Ozone variability and trends in the UTLS derived from the IAGOS- CARIBIC observatory using JETPAC, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7734, https://doi.org/10.5194/egusphere-egu2020-7734, 2020.

The ozone layer was damaged last century due to the emissions of long-lived ozone depleting substances (ODSs). Following the Montreal Protocol that banned ODSs, a reduction in total column ozone (TCO) ceased in the late 1990s. Today, ozone above 32 km displays a clear recovery. Nevertheless, a clear detection of TCO recovery in observations remains elusive, and there is mounting evidence of decreasing ozone in the lower stratosphere (below 24 km) in the tropics out to the mid-latitudes (30-60°). Chemistry climate models (CCMs) predict that lower stratospheric ozone will decrease in the tropics by 2100, but not at mid-latitudes.
 
Here, we compare the CCMVal-2 models, which informed the WMO 2014 ozone assessment and show similar tendencies to more recent CCMI data, with observations over 1998-2016. We find that over this period, modelled ozone declines in the tropics are similar to those seen in observations and are likely driven by increased tropical upwelling. Conversely, CCMs generally show ozone increases in the mid-latitude lower stratosphere where observations show a negative tendency. We provide evidence from JRA-55 and ERA-Interim reanalyses indicating that mid-latitude trends are due to enhanced mixing between the tropics and extratropics, in agreement with other studies. 

Additional analysis of temperature and water vapour further supports our findings. Overall, our results suggest that expected changes in large scale circulation from increasing greenhouse gases may now already be underway. While model projections suggest extra-tropical ozone should recover by 2100, our study raises questions about their ability to simulate lower stratospheric changes in this region.

How to cite: Ball, W., Chiodo, G., Abalos, M., and Alsing, J.: Comparison of observed lower stratospheric ozone changes with free-running chemistry climate models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16138, https://doi.org/10.5194/egusphere-egu2020-16138, 2020.

The quasi-biennial oscillation (QBO) is the dominating mode of variability in the tropical stratosphere. The oscillation of zonal winds between downward propagating easterlies and westerlies induces a secondary meridional circulation. This, in turn, modulates tropical upwelling, which also affects transport between tropical and extratropical regions and can induce large swings in tracer anomalies. Chemistry-climate models (CCMs) need a sufficiently high vertical resolution to spontaneously generate a QBO, while models with lower resolution often nudge zonal winds to observed equatorial wind profiles. Here, we evaluate the QBO impact on lower stratospheric ozone variability in the CCM SOCOLv3 using various model set-ups. Composites of stratospheric ozone observations demonstrate large interannual variations in mid-latitudes driven by QBO phase-dependent variability. From a large ensemble of free-running model simulations with nudged QBO, we find simulated ozone anomalies in the tropical stratosphere consistently reproduce those observed. However, extratropical anomalies show significant deviations from observations. In the southern hemisphere, about 65% of all cases from our ensemble agree in the sign of the observed anomalies, but the amplitude is underestimated. In contrast to the free-running model, simulations in specified dynamics mode show an overall good agreement with observations, including extratropical regions. This suggests a strong impact of the state of the large-scale stratospheric circulation on the QBO effect upon mid-latitudes. This is supported by model simulations where specified dynamics are applied to the troposphere only. Here we present a detailed analysis of the interaction between simulated stratospheric circulation and the QBO-induced secondary circulation. The realistic representation of such QBO-driven events in terms of frequency and strength in CCMs may be crucial for reproducing the observed large interannual variability in lower stratospheric tracer concentrations and, hence, for correctly retrieving lower stratospheric ozone trends.

How to cite: Stenke, A., Ball, W. T., and Domeisen, D.: The QBO as driver of lower stratospheric ozone variability as quantified in the CCM SOCOLv3, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16682, https://doi.org/10.5194/egusphere-egu2020-16682, 2020.

Intercomparisons between Chemistry-Climate Models (CCMs) have highlighted shortcomings in our understanding and/or modeling of long-term ozone trends, and there is a growing interest in the impact of stratospheric ozone changes on tropospheric chemistry via both ozone fluxes (e.g. from the projected strengthening of the Brewer-Dobson circulation) and actinic fluxes. Advances in this area require a good understanding of the modelling uncertainties in the present-day distribution of stratospheric ozone, and a correct attribution of these uncertainties to the processes governing this distribution: photolysis, chemistry and transport. These processes depend primarily on solar irradiance, temperature and dynamics.

Here we estimate model uncertainties arising from different input datasets, and compare them with typical uncertainties arising from the transport and chemistry schemes. This study is based on four sets of tightly controlled sensititivity experiments which all use temperature and dynamics specified from reanalyses of meteorological observations. The first set of experiments uses one Chemistry-Transport Model (CTM) and evaluates the impact of using 3 different spectra of solar irradiance. In the second set, the CTM is run with 4 different input reanalyses: ERA-5, MERRA-2, ERA-I and JRA-55. The third set of experiments still relies on the same CTM, exploring the impact of the transport algorithm and its configuration. The fourth set is the most sophisticated as it is enabled by model developments for the Copernicus Atmopshere Monitoring Service, where the ECMWF model IFS is run with three different photochemistry modules named according to their parent CTM: IFS(CB05-BASCOE), IFS(MOCAGE) and IFS(MOZART).

All modelling experiments start from the same initial conditions and last 2.5 years (2013-2015). The uncertainties arising from different input datasets or different model components are estimated from the spreads in each set of sensitivity experiments and also from the gross error between the corresponding model means and the BASCOE Reanalysis of Aura-MLS (BRAM2). The results are compared across the four sets of experiments, as a function of latitude and pressure, with a focus on two regions of the stratosphere: the polar lower stratosphere in winter and spring - in order to assess and understand the quality of our ozone hole forecasts - and the tropical middle and upper stratosphere - where noticeably large disagreements are found between the experiments.

How to cite: Chabrillat, S., Huijnen, V., Errera, Q., Debosscher, J., Bouarar, I., Brasseur, G., Belamari, S., Marécal, V., Josse, B., and Flemming, J.: Beyond model spread: a process-based attribution of uncertainties in stratospheric ozone modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19734, https://doi.org/10.5194/egusphere-egu2020-19734, 2020.

Understanding the sinks, sources and transport processes of stratospheric trace gases can improve our prediction of mid to long term climate change. In this study we consider the processes that lead to variability in stratospheric water vapor. We perform a Multiple Linear Regression(MLR) on the SWOOSH combined anomaly filled water vapor product with ENSO, QBO, BDC, mid-tropospheric temperature, and CH4 as predictors, in an attempt to find the factors that most succinctly explain observed water vapor variability. We also consider the fraction of entry water vapor variability that can be accounted for by variations of the cold point temperature as an upper bound on how much water vapor variability is predictable from large scale processes. Several periods in which the MLR fails to account for interannual variability are treated as case studies in order to better understand variability in entry water not governed by these large scale processes.

How to cite: Ziskin Ziv, S. and I. Garfinkel, C.: Revisiting the factors that drive interannual variability in stratospheric entry water vapour, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5231, https://doi.org/10.5194/egusphere-egu2020-5231, 2020.

Stratospheric water vapor variations play an important role on the climate. Predictions of changes in stratospheric humidity are uncertain because of gaps in our understanding of physical processes occurring in the TTL, between 14 and 20 km altitude. In particular, climate models have great difficulties in modelling water vapor variations in the TTL due to a poor representation of tropical convection, which largely controls the vertical transport of water vapor to UTLS, among other things.

One of the scientific objectives of the CONCIRTO⁵ program is to better understand the role of marine deep convective systems, and tropical cyclones in particular, on the hydration of TTL in the Southwestern Indian Ocean.  In March 2017, a rapid deepening of the tropical cyclone Enawo occured north-west of Reunion island before to strike and cross Madagascar from north to south. The progressive intensification of the cyclone to the intense tropical cyclone stage makes it an ideal case study to analyze the transport of water vapor and hydrometeors in the TTL according to the intensity phase of the cyclone. 

We will present modelling results on water vapor transport into the TTL in March 4 during ENAWO’s intensification. On March 4, the mesoscale model Meso-NH simulated a large water vapour transport through the TTL, associated with the injection of ice through the tropopause and the observation of cirrus clouds. The model validation is done by comparison with satellite data (CALIPSO, Meteosat-8). We generalize the intrusion modelling during ENAWO intensification by comparing the brightness temperature observed above the tropical cyclones and the tropical tropopause temperature extracted from ECMWF-Analysis during the 2016-2017 cyclonic season. From these studies, we can estimate the number of intrusions during a cyclonic season and the cyclonic intensity associated with the intrusions.

⁵Effects of convection and cirrus clouds on the Tropical Tropopause Layer over the Indian Ocean

How to cite: Héron, D., Evan, S., Brioude, J., Pianezze, J., Dauhut, T., Noel, V., Bielli, S., Barthe, C., and Cammas, J.-P.: Hydration of the tropical tropopause layer (TTL) by convective updraft during tropical cyclone ENAWO(2017) and generalization to tropical storms in the southwestern Indian Ocean in summer 2016-2017., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12643, https://doi.org/10.5194/egusphere-egu2020-12643, 2020.

We present new observations of trace gases in the stratosphere based on a cost-effective sampling technique that can access much higher altitudes than aircraft. The further development of this method now provides detection of species with abundances in the parts per trillion (ppt) range and less. We focus on mixing ratios for CFC-11 and CFC-12 which are important for understanding stratospheric ozone depletion and circulation. After demonstrating the quality of the data through comparisons with ground-based records and aircraft-based observations we combine them with the latter to demonstrate their potential. We first compare them with results from a global model driven by three widely used meteorological reanalyses (ERA-Interim, JRA-55, MERRA-2). Secondly, we focus on CFC-11 as recent evidence has indicated renewed atmospheric emissions of that species relevant on a global scale. Because the stratosphere represents the main sink region for CFC-11, potential changes in stratospheric circulation and troposphere-stratosphere exchange fluxes have been identified as the largest source of uncertainty for the accurate quantification of such emissions. Our observations span over a decade (up until 2018) and therefore cover the period of the slowdown of CFC-11 global mixing ratio decreases measured at the Earth’s surface. The spatial and temporal coverage of the observations is insufficient for a global quantitative analysis, but we do find some trends that are in contrast with expectations; indicating that the stratosphere may have contributed to tropospheric changes. Further investigating the model data we find that the required dynamical changes in the stratosphere required to explain the apparent change in tropospheric CFC-11 emissions after 2013 are possible, but with a very high uncertainty range in the change of stratosphere-to-troposphere flux of CFC-11. This is partly caused by the high variability of mass flux from the stratosphere to the troposphere, especially at time scales of a few years, and partly by large differences between runs driven by different reanalysis products, none of which agree with our observations well enough for such a quantitative analysis.

How to cite: Laube, J. and Ploeger, F. and the Stratospheric CFC-11 team: Investigating stratospheric changes between 2009 and 2018 with aircraft, AirCores, a global model and a focus on CFC-11, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13903, https://doi.org/10.5194/egusphere-egu2020-13903, 2020.

Man-made halogenated compounds emitted from the Earth’s surface ultimately reach the stratosphere where they undergo photolysis, leading to three main fluorine reservoirs: hydrogen fluoride (HF), carbonyl fluoride (COF₂) and carbonyl chloride fluoride (COClF). This process is directly influenced by the strength of the mean meridional circulation of the stratosphere, the Brewer-Dobson Circulation (BDC). The BDC is projected to speed-up with the greenhouse gases induced global warming. However, studies have highlighted a multiyear variability in the strength of the BDC resulting in hemispheric asymmetries in observed and modelled trends of age of air and long-lived tracers.

Total inorganic fluorine (F_y, the fluorine weighted sum of HF, COF₂ and COClF) is used here as a tracer of the stratospheric circulation changes. We perform an analysis and interpretation of Fourier transform infrared (FTIR) multidecadal time-series of HF and COF₂ from the Jungfraujoch (Switzerland, 46.55°N) and Lauder (New-Zealand, 45.03°S) stations and from the space-borne Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS). Indeed, the summation of HF and COF₂ is a very good proxy of F_y as we determine, from ACE-FTS and the chemical-transport model (CTM) TOMCAT, that COClF is only accounting for less than 5% of the total F_y budget.

The kinematic CTM BASCOE (Belgian assimilation system for chemical observations) is used here to assess the representation of the investigated circulation changes in four state-of-the-art meteorological reanalyses, i.e., ERA-Interim, JRA-55, MERRA and MERRA-2. We also investigate if WACCM4 (Whole Atmosphere Community Climate Model version 4) is able to reproduce these changes through a free-running simulation.

The ground-based and satellite FTIR time-series of COF₂ show contrasting results over their common time period (2004-2019), with a positive total column trend above the Jungfraujoch, and a non-significant (ground-based) or decreasing trend (ACE-FTS) above Lauder. We find large discrepancies between the BASCOE-CTM simulations, with MERRA-2 inducing overly large simulated F_y total columns which could confirm the weaker tropical upwelling highlighted in previous age of air studies.

How to cite: Prignon, M., Bernath, P. F., Chabrillat, S., Chipperfield, M. P., Dhomse, S. S., Feng, W., Minganti, D., Servais, C., Smale, D., and Mahieu, E.: Impacts of stratospheric dynamical variability on total inorganic fluorine from observations and models constrained by state-of-the-art reanalyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16999, https://doi.org/10.5194/egusphere-egu2020-16999, 2020.

In order to monitor possible changes of the mean age of air in the stratosphere, in situ high altitude observations of suitable tracers are required. The AirCore is a simple sampling technique, which can be deployed to weather balloons in order to capture a continuous vertical profile of atmospheric trace gases up to 30 km. During ascent it empties due to the decreasing ambient pressure with height. During descent the AirCore fills with ambient air due to the positive change in ambient pressure. The analysis results from a continuous gas analyzer are merged with the recorded in-flight information to obtain the vertical distribution of the target trace gases mole fractions.

In context of the Goethe-University data processing procedure, an instantaneous pressure equilibrium is assumed across the whole AirCore. Since the amount of collected air sample is especially low at high altitudes, the assumptions made for data processing affect the accuracy of the altitude attribution primarily in the stratosphere. In order to evaluate the sample-to-altitude attribution procedure, the setup for an altitude dependent CO-spiking experiment was developed, tested and deployed to an AirCore that was flown and analyzed in Traînou, France, in June 2019. This setup allows for releasing small spikes of high CO signal gas in the inlet of the AirCore during descent at predefined GPS altitudes. By assigning the associated mole fraction measurements to the sampling altitude, the spiking signals are assigned to a modelled altitude as well. The quality of the altitude retrieval can be evaluated by comparing the assigned signal altitudes to the GPS release altitudes. In principle, every laboratory can deploy this experiment to its respective AirCores in order to evaluate its altitude attribution quality. Here we present the experimental details and the results of the evaluation to show the accuracy of the altitude registration of Goethe-University AirCore profiles. In addition, the long-term time series of mid-latitude stratospheric mean age observations from Engel et al 2017 is extended with mean age calculated from CO₂-profiles obtained from recent AirCore observations.

How to cite: Wagenhäuser, T., Engel, A., Sitals, R., and Kistner, I.: Mean Age from in situ observations with AirCore: Accuracy of altitude attribution investigated with the CO-spiking experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19192, https://doi.org/10.5194/egusphere-egu2020-19192, 2020.

Spectroscopic direct sun remote sensing of the atmosphere offers an essential tool for the validation of models and satellite observations as well as for the monitoring of emissions. Validation missions for greenhouse gas monitoring satellites are essential to improve the performances of the satellite products, thereby gaining a better understanding of the dynamics between sources and sinks. Furthermore, the monitoring of ozone-depleting substances is a vital contribution to observe the progress in restoring the ozone layer. A high tracking precision is in particular for measuring CO₂ and CH₄ columns required. We aim for an accuracy better than 0.05°.

This work presents the development of a compact and reliable stand-alone sun tracker for mobile applications. The tracking is camera-based and has two modes. In the first mode, image processing using the image of a fish-eye lens with a field of view of 185° monitoring the entire hemisphere above the instrument calculates the coarse position of the sun. On reaching this coarse position, the other camera-based tracking system takes over and centers the projection of the sun with high precision and fast response times (100 Hz control loop). The tracker is compatible with different kinds of spectrometers like grating spectrometers and Fourier transform infrared spectrometers (FTIR). The tracking is also suitable for different mobile platforms like cars, ships, or stratospheric balloons. 

During the CoMet (Carbon Dioxide and Methane Misson 2018) campaign, the tracking has performed well in a stop and go manner on a car-mounted setup. On every stop, the tracker was able to autonomously find the sun regardless of the relative position of the vehicle. For the MORE-2 (Measuring Ocean REferences 2) campaign onboard a research vessel over the Pacific ocean, the tracking allowed for using over 99 % of the measuring time for high-precision retrievals of CO₂ and CH₄ using an EM27/SUN FTIR. Based on the lessons learned during the performed campaigns, a further improved version of the tracker for flying on a stratospheric balloon in August 2020 is in development. 

How to cite: Kleinschek, R., Kostinek, J., Holzbeck, P., Knapp, M., Luther, A., Hase, F., and Butz, A.: Development of a Fast Solar Tracker Enabling Atmospheric Direct Sun Remote Sensing Applications on Different Moving Platforms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9596, https://doi.org/10.5194/egusphere-egu2020-9596, 2020.

Recent intercomparison exercises have been conducted at two European NDACC lidar sites.  The mobile NASA Stratospheric Ozone Lidar (NASA STROZ) was present for a two part validation campaign at the Observatoire de Haute-Provence (43.93 N, 5.71 E) in July 2017 and March 2018 and at the Hohenpeißenberg Meteorological Observatory (47.80 N, 11.00 E) in March 2019.  Lidar profiles of ozone and temperature were compared with local radiosondes and ozonesondes; satellite profiles from local overpasses of Sounding of the Atmosphere by Broadband Emission Radiometry instrument (SABER) and Microwave Limb Sounder (MLS); and NCEP reanalysis. There is overall good agreement between all the lidar instruments and the balloon measurements, particularly in the reproduction of small scale features, during all three phases of the European campaign.  

We have conducted a detailed correlational study of all instruments involved in the campaign and have rigorously evaluated the uncertainty budget of each instrument.  We will discuss the strengths and drawbacks of different statistical techniques for evaluating coincident ozone and temperature measurements and compare how our estimates of instrument uncertainty compare to the observed variance in the data.

How to cite: Wing, R., Steinbrecht, W., Godin-Beekmann, S., McGee, T. J., Sullivan, J., Sumnicht, G., Ancellet, G., Hauchecorne, A., Khaykin, S., and Keckhut, P.: NDACC Lidar Validation Activities in Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22092, https://doi.org/10.5194/egusphere-egu2020-22092, 2020.