The Asian summer monsoon Chemical and Climate Impacts Project (ACCLIP) is a large airborne field campaign conducted over the Western Pacific in summer 2022. The campaign deployed two research aircraft, the NCAR Gulfstream V (GV) and the NASA WB-57, both with extensive payload of chemistry and microphysics measurements for trace gas and aerosol content to investigate the Asian monsoon convective outflow at the UTLS levels. The campaign also included ground-based balloon soundings and extensive collaborative measurements in the region. Based from Osan, Republic of Korea, a total of 29 research fights were conducted covering the vertical range of 300 ft above sea level to ~70 hPa over a large domain of western Pacific (15°N-43°N, 125°E-155°). These measurements provide novel information on the role of Asian summer monsoon in altering atmospheric composition, serving as a distinct linkage between the weather and the climate through its impact on ozone chemistry and aerosol radiative effect. Observational highlights and initial indications of post campaign data analysis and modeling will be presented in this overview.

How to cite: Pan, L., Newman, P., Atlas, E., Thornberry, T., Randel, B., and Toon, B.: Highlights of the ACCLIP Campaign 2022: Operations and Science, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3654, https://doi.org/10.5194/egusphere-egu23-3654, 2023.

The Asian summer monsoon Chemical and Climate Impact Project (ACCLIP) used the NSF/NCAR Gulfstream V (GV) research aircraft, the NASA WB-57f research aircraft, the Korean NARA King Air, and a broad set of balloon launches to investigate atmospheric processes that influence ozone depletion and climate in the Korea/Japan region.  The WB-57 and NSF GV part of the field campaign was flown from Osan Air Base, Republic of Korea during the July-August 2022 period.

This presentation will show some of the dynamical and transport aspects of the Asian summer monsoon anti-cyclone (ASMA) during the summer of 2022. In particular, the strength and flow aspects of the ASMA will be illustrated and shown in the context of an ASMA MERRA-2 climatology. Flight overviews against this flow field will be compared against detrainment events from the ASMA from Asia into the Pacific Ocean. Flight profiles will also show how ACCLIP made extensive sampling of the ASMA’s eastern flank – mapping of the vertical and horizontal structure in the upper troposphere and lower stratosphere.

How to cite: Newman, P. A., Pan, L., Elliot, A., William, R., Thornberry, T., Toon, O. B., Ueyama, R., Lait, L., and Nash, E.: The Dynamical Background to the 2022 Asian Summer Monsoon Chemical and Climate Impacts Project (ACCLIP), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2948, https://doi.org/10.5194/egusphere-egu23-2948, 2023.

We examine the role of the Asian Summer Monsoon (ASM) in influencing the chemical composition of the upper troposphere and lower stratosphere (UTLS) using the Whole Atmosphere Community Climate Model, version 6 (WACCM6). This version of WACCM6 uses a Finite Volume dynamical core, with a horizontal resolution of ~1.0º and a vertical resolution of ~500m in the UTLS. For this study, the specified dynamics option is applied where the temperature, zonal and meridional winds are nudged towards MERRA-2 reanalysis fields from the NASA Goddard Earth Observing System version 5 (GEOS5). This model study examines the relative contribution of anthropogenic and lightning nitrogen oxide (NOx) sources in the UTLS during the Asian Summer Monsoon (ASM) using a tagged NOx mechanism (Emmons et al., Geosci. Model Dev., doi:10.5194/gmd-5-1531-2012). In this tagging mechanism, the NOx source regions in South and East Asia are examined separately. NOx sources from outside South and East Asia and the amount transported from the stratosphere are also derived. The model simulated NOx for the year 2022 is evaluated by comparing it to in situ measurements from the Asian summer monsoon Chemical and Climate Impact Project (ACCLIP). The model results suggest that the major contribution of NOx concentration within the ASM anticyclone is from South Asia lightning and South Asia anthropogenic sources, which contribute more than 55% to the upper troposphere NOx for the year 2022. In the shedding region, both South and East Asia anthropogenic emissions play an important role in the NOx budget. In addition, we also explore the hydroxyl radical (OH) and peroxyacetylnitrate (PAN) formation from different NOx sources, which are of importance to atmospheric compositions such as ozone and aerosols in the free troposphere.

How to cite: Zhang, J., Kinnison, D., Tilmes, S., Emmons, L., Smith, W., Honomichl, S., Franchin, A., Liang, Q., and Pan, L.: Relative Contributions of Anthropogenic and Lightning Nitrogen Sources in the Upper Troposphere during the Asian Summer Monsoon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8406, https://doi.org/10.5194/egusphere-egu23-8406, 2023.

Tropopause-overshooting convection in the midlatitudes provides a rapid transport pathway of air from the lower troposphere to the upper troposphere and lower stratosphere (UTLS), and can result in the formation of above-anvil cirrus plumes (AACPs).  Recent in situ observations from the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign are used to examine impacts from active overshooting convection on UTLS composition. There are little to no prior airborne observations of active overshooting convection, making observations from this flight valuable to interpreting and exploring processes seen in idealized modeling studies. DCOTSS research flight 13 on May 31^st, 2022 sampled active overshooting convection over the state of Oklahoma for more than three hours with the NASA ER-2 high-altitude research aircraft. Additionally, an AACP was bisected during this flight, providing the first such extensive sampling of this phenomena. This study aims to provide a detailed understanding of changes in the UTLS composition from active overshooting convection and AACPs using the in-situ observations from this flight. The observations reveal multiple pronounced changes in air mass composition and stratospheric hydration. In agreement with prior modeling studies, maximum altitudes of water vapor enhancement were much higher than altitudes of mostly passive trace gas composition change. Stratospheric water vapor enhancements reached nearly a factor of four over background levels at a maximum altitude of 16.56 km and a potential temperature of 389.76 K. Carbon monoxide, a tracer of tropospheric origin, showed enhancements of a factor of two over background levels at a maximum altitude of 15.76 km and potential temperature of 363.6 K. There is a notable positive correlation between water vapor and ozone near the bisection of the AACP, which seems to be the result of horizontal mixing. It appears that the water vapor enhancement within the AACP was limited to the saturation mixing ratio of the low temperature environment.

How to cite: Gordon, A., Homeyer, C., Smith, J., Bui, T. P., Dean-Day, J., Hanisco, T., Hannun, R., St Clair, J., Wofsy, S., Pittman, J., Daube, B., Sayres, D., and Pandey, A.: Detailed Examination of Upper Troposphere Lower Stratosphere Composition Change from In Situ Observations of Active Convection in the United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9693, https://doi.org/10.5194/egusphere-egu23-9693, 2023.

On 24 June 2022, remnant outflow from a tornadic supercell storm that occurred in northern Kansas on the evening of 23 June 2022 was observed by the high-altitude NASA ER-2 aircraft during the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign. Namely, preliminary analysis indicates that stratospheric water vapor enhancements were observed at altitudes up to approximately 19.25 km (~1 km higher than any prior documented event), approximately 460 K potential temperature (~30 K higher than any prior documented event), and ozone mixing ratios of more than 1400 ppbv (more than double any prior documented event). The responsible storm was one of the most extreme events observed annually in the United States, within no more than 10 per year such high-reaching storms based on ground-based radar climatology. Here, we review the event using high-resolution ground-based radar volumes and satellite imagery and show that it reached altitudes exceeding 19 km for at least an hour. Linkages to the Kansas storm will be demonstrated via trajectory analyses initialized in the volumes impacted by the storm (as determined from radar and satellite observations). Broader evaluation of stratospheric composition impacts resulting from this event will also be presented. 

How to cite: Homeyer, C., Smith, J., Bui, T., Dean-Day, J., Hanisco, T., Hannun, R., St Clair, J., and Bedka, K.: A Case Study of the Highest Ever Altitude of In Situ Observations of Convective Hydration of the Stratosphere during the DCOTSS Field Campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9858, https://doi.org/10.5194/egusphere-egu23-9858, 2023.

Airborne research missions were conducted during the summer season over the Western Pacific downwind of the Asian summer monsoon (ACCLIP, Asian Summer Monsoon Chemical & CLimate Impact Project, Aug/Sept., 2022) and over central N. America (DCOTSS: Dynamics and Chemistry Of The Summer Stratosphere, July/Aug., 2021 and May/July, 2022).  A major objective of both of these missions was to characterize the impact of convective transport of trace gases on regional and hemispheric air quality and on ozone chemistry in the UT/LS.  The DCOTSS campaign focused on outflow from overshooting convection, and ACCLIP targeted outflow and eddy-shedding from the Asian summer monsoon anticyclone.  Whole air samples were collected from the three aircraft deployed during the missions (NSF GV, NASA WB-57, and NASA ER2), and a wide range of organic trace gases were measured that included NMHC, long and short-lived halocarbons and organic nitrates.   In-situ measurements of ozone and other trace gases were also included in the airborne instrument payloads.  Both campaigns showed cases of tropospheric transport into UT/LS region, with significantly larger amounts of certain trace gases (e.g., dichloromethane and others) found in the ACCLIP region.  This presentation will provide an overview of selected trace gas distributions and correlations from these campaigns to illustrate the role of the different monsoon regions on the chemistry of the UT/LS.

How to cite: Atlas, E., Smith, K., Treadaway, V., Schauffler, S., Hendershot, R., Lueb, R., Donnelly, S., Pope, L., Pan, L., Thornberry, T., Newman, P., and Bowman, K. and the ACCLIP and DCOTSS Science Teams: Impact of convection on trace gas composition during the summer monsoon season downwind of East Asia and over central North America, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4449, https://doi.org/10.5194/egusphere-egu23-4449, 2023.

The summertime Asian Monsoon (AM) is the single most important contributor to water vapor in the UTLS and overworld stratosphere. Much of that water comes from sublimating ice, but the life cycle of the condensate lofted by overshooting convection is not well understood. We report here on insights into that life cycle derived from the first in-situ measurements of water vapor isotopic composition over the Asian Monsoon. The Chicago Water Isotope Spectrometer (ChiWIS) flew on high-altitude aircraft in the monsoon center during the StratoClim (2017) campaign out of Nepal, and in monsoon outflow during ACCLIP (2022) out of South Korea. Both campaigns sampled a broad range of convective and post-convective conditions, letting us trace how convective ice sublimates, reforms, and leaves behind characteristic isotopic signatures. We use the Bin Resolved Isotopic Microphysical Model (BRIMM), along with TRACZILLA backtrajectories and convective interactions derived from cloud-top products, to follow the evolving isotopic composition along flight paths in both campaigns. Results support the wide diversity of isotopic enhancements seen in both campaigns and show how temperature cycles downstream of convective events progressively modify environmental isotopic compositions.

How to cite: Clouser, B., KleinStern, C., Khaykin, S., Singer, C., Sarkozy, L., Viciani, S., Bianchini, G., D'Amato, F., Lykov, A., Ulanovsky, A., WIenhold, F., Legras, B., Homeyer, C., Thornberry, T., and Moyer, E.: Microphysical Modeling of Water Isotopic Composition in the Asian Summer Monsoon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14405, https://doi.org/10.5194/egusphere-egu23-14405, 2023.

During the StraoClim Geophysica campaign, moist air with total water mixing ratios up to 200 ppmv was observed within the Asian Summer Monsoon anticyclone, above the local cold point tropopause (CPT). High ozone mixing ratios of up to 250 ppbv suggest substantial stratospheric moistening. We used 60-day back- and forward trajectories to classify the observations into two groups based on their distance to the Lagrangian dry point (LDP): those where the LDP has just occurred or is still expected to occur (type A, 0-3 days from LDP), and those where the LDP was passed 15-35 days before (type B). We applied a microphysical box model (CLaMS-Ice) and a simple freeze drying model (FDM) to simulate the evolution of ice mixing ratios along the trajectories. Type A air masses, with ice mixing ratios larger than 1 ppm, underwent multiple transitions between the solid and gas phase, in good agreement with CALIPSO ice and MLS water vapor observations of around 5 ppm. In contrast, type B air masses showed less agreement with CALIPSO ice and significantly overestimated MLS observations when CLaMS-Ice or FDM were applied. However, water vapor reconstructed from the LDP of the merged back- and forward trajectories agreed much better with MLS, indicating that the wet air masses of type B, observed up to 1.7 km above the CPT, are not representative of the large-scale water vapor distribution detected by MLS. Our results suggest that the full backward and forward evolution of the sampled air masses needs to be considered when inferring stratospheric moistening in the Asian monsoon region. Water vapor concentrations set by LDPs seem to be a better proxy for the stratospheric water vapor budget than rare observations of enhanced water mixing ratios above the local CPT. These observations call into question their applicability to quantify long-term stratospheric water vapor trends.

How to cite: Konopka, P., Rolf, C., von Hobe, M., Khaykin, S. M., Clouser, B., Moyer, E., Ravegnani, F., Viciani, S., Afchine, A., Krämer, M., Stroh, F., and Ploeger, F.: A long way of water vapor from the Asian Summer Monsoon into the stratosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8021, https://doi.org/10.5194/egusphere-egu23-8021, 2023.

Several studies have found that the summertime Asian Summer Monsoon (ASM) anticyclone is linked to a persistent enhancement of carbon monoxide (CO) concentrations in the Upper Troposphere and Lower Stratosphere (UTLS).

In this study, more than 15 years (2008-2022) of satellite observations from Eumetsat’s Infrared Atmospheric Sounding Interferometer (IASI) are used to investigate the interannual, seasonal and sub-seasonal variability of CO in the UTLS during the ASM. To assess the ability of IASI CO data to characterize the UTLS monsoon circulation, we focus on the Asian Summer Monsoon Chemical & CLimate Impact Project (ACCLIP) campaign that took place in summer 2022 in Korea. Several case studies associated with the presence of eddy shedding features are presented. Simulations from the Goddard Earth Observing System (GEOS) model performed during the ACCLIP campaign period are also used to support the IASI data analysis and interpretation.

How to cite: Boynard, A., Viatte, C., Sinnathamby, S., Safieddine, S., Pan, L., Honomichl, S., Smith, W., Liang, Q., and Clerbaux, C.: What does IASI see during the Asian Summer Monsoon over the west Pacific?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4565, https://doi.org/10.5194/egusphere-egu23-4565, 2023.

The Asian Summer Monsoon (ASM) provides one of the most effective transport pathways to deliver surface pollution into the stratosphere and impact stratospheric composition and climate. To better understand the impact of ASM, the Asian summer monsoon Chemical and Climate Impact Project (ACCLIP) took place in South Korea from July 29 – Sep 2, 2022.  During ACCLIP, in situ measurements of a wide range of trace gas, including carbon monoxide (CO), and aerosol species in the Upper Troposphere and Lower Stratosphere (UT/LS) were collected.

CO is a key pollutant emitted from anthropogenic emissions, as well as biogenic and biomass emissions, along with many other precursors for ozone and aerosol. In addition, its > 30-day atmospheric lifetime and linear chemical loss rate make it a key marker tracer for atmospheric pollution transport and ozone photochemistry. In this study, we use CO simulated by the NASA GEOS model to (1) analyze the ACCLIP-2022 observations, (2) examine surface-to-stratosphere transport in the Asian Summer Monsoon region during the summer of 2022, (3) assess how transport in 2022 is similar to or different from the 2005-2021 Climatology.  In addition, we use idealized tagged CO tracers that are used track pollution transport from a suite of source regions, e.g., within East Asia, South Asia, and Southeast Asia, to quantify the contribution of these target regions to CO and air mass abundance in the lower stratosphere over Asia and downwind regions.

How to cite: Liang, Q., Bian, H., Chin, M., Pan, L., Newman, P., and Kinnison, D.: The 2022 Asian Summer Monsoon Transport and its Connection to the 2005-2021 Climatology as Illustrated by Carbon Monoxide, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2828, https://doi.org/10.5194/egusphere-egu23-2828, 2023.

We present our study on the sub-seasonal variability of UTLS aerosols and CO that is a result of the variability induced by the sub-seasonal variability of the Asian summer monsoon dynamics. We use the NASA global model GEOS simulations that incorporates emissions from anthropogenic, biomass burning, volcanic, and other natural sources to simulate CO, aerosols and related gases and the model experiments separating source types (anthropogenic, biomass burning, volcanic) and source locations (East Asia, South Asia). With model results and observations from recent aircraft measurements (StratoClim, ACCLIP) in the UTLS over the Asian summer monsoon regions, we will discuss (1) the sub-seasonal variability of transport pathways of surface-generated pollutants to reach UTLS, and (2) sub-seasonal variation of aerosol composition that is determined by the variability of source type originating in different locations.

How to cite: Chin, M., Bian, H., Colarco, P., Lait, L., and Chen, G.: Sub-seasonal variability of Asian summer monsoon transport of aerosols and CO to the UTLS in the context of recent aircraft observations in the Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2131, https://doi.org/10.5194/egusphere-egu23-2131, 2023.

Balloon soundings within the Asian summer monsoon anticyclone (ASMA) were conducted from Osan, South Korea as part of the Asian Summer Monsoon Chemical and Climate Impact Project (ACCLIP) in August of 2022. Over 30 soundings in 12 days were accomplished with high resolution co-located in situ profiles of aerosol size distributions, water vapor, ozone, and state parameters from the surface to the lower stratosphere. Aerosol measurements included accumulation mode particle size and number concentrations with Printed Optical Particle Spectrometers (POPS), coarse mode measurements with LASP Optical Particle Counters (LOPC), and total aerosol between 20 nm and 10 µm with Stratospheric Total Aerosol Counters (STAC). The aerosol sondes observed a pervasive Asian Tropopause Aerosol Layer (ATAL) and temperature dependent microphysical trends that are consistent with the location of the cold-point tropopause and lapse rate minimum. Simultaneous flights with cryogenic frostpoint hygrometers (EN-SCI CFH) and ozonesondes (EN-SCI ECC) provided context on the UTLS mixing processes in the ASMA through tracer-tracer relationships. Model reanalysis products suggest that the soundings were within the ASMA domain and back trajectories indicate sampling of fresh and aged airmasses within the UTLS transported from the ASMA circulation. These measurements add to the limited record of aerosol and water vapor observations of the Asian UTLS during the summer monsoon and provide an understanding of the ATAL that can only be gathered from continuous vertical profiles.

How to cite: Goetz, J. D., Kalnajs, L., Kim, J., Norgren, M., Kindel, B., Kim, H.-G., and Kang, H.: Balloon-borne in situ profiles of aerosol, water vapor, and ozone within the Asian summer monsoon anticyclone during the ACCLIP 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7973, https://doi.org/10.5194/egusphere-egu23-7973, 2023.

The Asian monsoon anticyclone transports aerosol and gas phase pollutants from the boundary layer to the upper troposphere and lower stratosphere, from whence they are transported out over the Western Pacific by eddy shedding. This significantly increases aerosol loading in the upper troposphere and maintains a layer of aerosol in the lowermost stratosphere with important implications for climate and stratospheric chemistry. Models show large spread in the spatial distribution and microphysical properties of aerosols transported by the Asian monsoon, and the chemical and radiative effects remain uncertain.

In August 2022 we measured aerosol size distributions in Asian summer monsoon outflow from two aircraft, the NCAR GV and NASA WB57, as part of the Asian Summer Monsoon Chemical Climate Impacts Project (ACCLIP). On both aircraft we operated a Nucleation Mode Aerosol Size Spectrometer (NMASS, a custom battery of 5 condensation particle counters) and a modified Ultra-High Sensitivity Aerosol Spectrometer (an optical particle counter from Droplet Measurement Technologies) to measure size distributions from 3 to 1500 nm at 1 Hz time resolution.

Here we use these data together with concurrently measured trace gases and reactive gases, and cloud properties, to quantify the transport of primary aerosol by the monsoon system, and the formation of secondary aerosol in the monsoon outflow. We show that new particle formation occurs in the upper troposphere in monsoon outflow and investigate its relation to lofting of condensable vapours and wet scavenging of larger aerosols by deep convection. We use data taken in the upper troposphere and lower stratosphere of the NASA Atmospheric Tomography Mission (ATom) to compare aerosol microphysical properties in the summer monsoon outflow with those in less anthropogenically influence air.

How to cite: Williamson, C., Simone, D., Brock, C., Lyu, M., Brown, M., Ziemba, L., Kim, J., Campos, T., Ullmann, K., and Pan, L.: Understanding the climate impacts of the Asian Summer Monsoon with in-situ observations of aerosol microphysical properties in the upper troposphere and lower stratosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1966, https://doi.org/10.5194/egusphere-egu23-1966, 2023.

The Asian Summer Monsoon Anticyclone (AMA) is known to bring ground-level pollutants up to the stratosphere. Aerosols in the AMA often form what is known as the Asian Tropopause Aerosol Layer (ATAL), with modelling studies suggesting that the ATAL can provide up to 15 % of the stratospheric aerosol in the Northern Hemisphere. In this work, we present single-particle mass spectrometry measurements of aerosol composition in the AMA outflow and in the North American upper troposphere/lower stratosphere (UTLS) during the same season. Measurements were taken by the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument and made during the Asian Summer Monsoon Chemical & CLimate Impact Project (ACCLIP). We find that the dominant aerosol type found in the ATAL and those found in the UTLS over North America are chemically different. Despite high concentrations of ground-level gas phase pollutants, particles in the ATAL are dominated by secondary nitrate particles. The organic content of these particles is low, which precludes them from being organic-nitrate aerosol; thus, we believe that these particles are either nitric/sulfuric acid solutions, or they are mixtures of partially neutralized ammonium nitrate/sulfate. Finally, we present the mass concentrations of nitrate particles, dust, and sulfate-organic particles in the ATAL, and estimate each particle type’s influence on the aerosol composition over the North American continent.

How to cite: Schill, G., Murphy, D., Lawler, M., and Abou-Ghanem, M.: Single-Particle Aerosol Composition in the Asian Tropopause Aerosol Layer and in the North American Upper Troposphere/Lower Stratosphere during ACCLIP, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9792, https://doi.org/10.5194/egusphere-egu23-9792, 2023.

The presence of aerosol particles in the upper troposphere/lower stratosphere (UTLS) region plays an important role for the Earth’s radiative balance and the formation of cirrus clouds. In recent years, a substantial amount of organic matter and ammonium nitrate have been found in the Asian upper troposphere (UT) associated with the Asian summer monsoon anticyclone (ASMA; Appel et al., 2022; Höpfner et al., 2019). These particles were observed at altitudes between 11 and 19 km (corresponding to potential temperatures between 355 and 420 K), known as the Asian Tropopause Aerosol Layer (ATAL).  However, the formation and aging processes of these particles remain unclear. In particular, the fate of aerosol particles in eastward eddy shedding events is poorly understood.

Here, we present the results of aircraft-based measurements in the eddy shedding region above the Western Pacific during the ACCLIP campaign in July/August 2022. Using the hybrid mass spectrometer ERICA (ERC instrument for chemical composition of aerosols; Hünig et al., 2022), the chemical composition of aerosol particles in the Asian UT was measured via a combination of two complementary aerosol mass spectrometry techniques: the desorption ionization technique (ERICA-LAMS) and the thermal desorption with subsequent electron impact ionization technique (ERICA-AMS). The detectable size range of ERICA extends from ~120 nm up to 3.5 µm.

Our ERICA-AMS measurements indicate that the ATAL above 360 K potential temperature exhibited enhanced concentrations of ammonium nitrate and organics with a growing fraction of sulfate towards higher altitudes. Additionally, measurements in aged ASMA air masses during eddy shedding events enabled the investigation of photochemical aging of particles originating from the ATAL. For this purpose, the degree of oxidation will be evaluated by the ratio of organic signals at m/z 43 and 44 from the ERICA-AMS. We will further combine the dataset from these observations with model results of the location and timing of recent convective influence. The determination of recent convective influence is based on kinematic backward trajectories and a satellite-derived database of convective cloud top altitudes to distinguish different source regions.

References:

Appel, O., Köllner, F., Dragoneas, A., et al.: Chemical analysis of the Asian tropopause aerosol layer (ATAL) with emphasis on secondary aerosol particles using aircraft-based in situ aerosol mass spectrometry, Atmos. Chem. Phys., 22, 13607–13630, https://doi.org/10.5194/acp-22-13607-2022, 2022.

Höpfner, M., Ungermann, J., Borrmann, S. et al.: Ammonium nitrate particles formed in upper troposphere from ground ammonia sources during Asian monsoons. Nat. Geosci., 12, 608–612, https://doi.org/10.1038/s41561-019-0385-8, 2019.

Hünig, A., Appel, O., Dragoneas, A., et al.: Design, characterization, and first field deployment of a novel aircraft-based aerosol mass spectrometer combining the laser ablation and flash vaporization techniques, Atmos. Meas. Tech., 15, 2889–2921, https://doi.org/10.5194/amt-15-2889-2022, 2022.

How to cite: Eppers, O., Köllner, F., Appel, O., Brauner, P., Ekinci, F., Molleker, S., Dragoneas, A., Hünig, A., Smith, W., Ueyama, R., Schneider, J., and Borrmann, S.: Chemical composition and processing of aerosol particles in the Asian Tropopause Aerosol Layer inferred from airborne measurements during the ACCLIP campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12081, https://doi.org/10.5194/egusphere-egu23-12081, 2023.

Stratospheric aerosols are an important component of Earth’s albedo, and therefore energy balance, and provide surface area for heterogeneous chemistry, which can lead to stratospheric ozone loss. Acquiring a comprehensive database of stratospheric aerosol, trace gas and dynamical observations to establish the baseline state and background variability of the stratosphere is essential to (1) developing a complete understanding of stratospheric dynamical and chemical processes that determine aerosol microphysics, radiative properties and heterogeneous chemistry, (2) evaluating the stratospheric response to natural and anthropogenic perturbations including climate change, volcanic eruptions, and potential climate intervention activities, and (3) strengthening the scientific foundation to inform policy decisions related to regulating global emissions that impact the stratosphere.

The NOAA Stratospheric Aerosol processes, Budget and Radiative Effects (SABRE) project is a multi-year, multi-deployment UTLS airborne science measurement program to study the microphysics, transport, chemistry and radiative properties of aerosols in the upper troposphere and lower stratosphere (UTLS).  The SABRE instrument payload and flight campaigns are designed to provide extensive, detailed measurements of aerosol size distributions, composition and radiative properties along with relevant trace gas species in different regions and seasons, which are critical for improving the ability of global models to accurately simulate the radiative, dynamical and chemical impacts of changes in stratospheric aerosol loading.

The first deployment of the SABRE project took place in February 2022, consisting of six flights from Ellington Field, Houston, TX. The flights provided an opportunity to field test several newly developed instruments that will be important for addressing SABRE science questions in subsequent deployments and sampled both the subtropical tropopause layer and midlatitude upper troposphere and lower stratosphere. The Realtime Air Quality Modeling System (RAQMS) was used for flight planning to target atmospheric dynamical features and species gradients. Complex structure was observed in trace gases and aerosol in the midlatitude UTLS, indicating significant stratosphere-troposphere exchange. Highlights from the deployment will be presented.

Subsequent SABRE deployments will target aspects of the stratospheric aerosol budget including high latitude processes with a deployment to Alaska in February-March 2023 and to the tropics to study Tropical Tropopause Layer (TTL) processes in 2024. Each deployment will also include flights from Houston, TX to investigate seasonal and interannual variability in the subtropical and midlatitude stratosphere.

How to cite: Thornberry, T. and Jensen, E.: The NOAA Stratospheric Aerosol processes, Budget and Radiative Effects (SABRE) Project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15699, https://doi.org/10.5194/egusphere-egu23-15699, 2023.

Nucleation of ultrafine aerosols near the tropical tropopause, followed by transport throughout the stratosphere by the Brewer-Dobson circulation, is thought to be the primary source of stratospheric aerosol number concentration.  However, depending on how rapidly the aerosols grow by condensation, many of the ultrafine particles generated by new particle formation (NPF) may be lost due to coagulation with accumulation-mode aerosols.  In this study, we use recent high-altitude aircraft measurements of aerosol size distribution, along with microphysical calculations, to investigate this issue.  Initial ultrafine and accumulation-mode size distributions are specified based on the aircraft measurements, and a bin microphysics model is used to simulate the evolution of the aerosol size distributions.  Coagulation and condensation of gases such as sulfuric acid, ammonia, and nitric acid are included.  Preliminary results indicate that for typical conditions, most of the ultrafine aerosols generated by NPF are removed by coagulation, resulting in a relatively small contribution to the total aerosol number concentration.  We have used the model to investigate the sensitivities of total number concentration evolution to aerosol size distributions and condensation rates.

How to cite: Jensen, E., Brock, C., Williamson, C., Ziemba, L., and Brown, M.: How much does new particle formation near the tropical tropopause contribute to stratospheric aerosol number concentration?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9166, https://doi.org/10.5194/egusphere-egu23-9166, 2023.

The stratospheric aerosol layer is important for stratospheric chemistry, climate change and in geo-engineering. Yet the processes governing the transport of sulfur to the stratosphere are poorly quantified. We present model calculations of the chemistry of sulfur dioxide (SO₂) and its transport to the stratosphere and perform numerous sensitivity runs to assess the range of uncertainty of these calculations. The transport model is based on backward trajectories from the ATLAS model driven by ECMWF ERA 5. A simplified chemical box model constrained by CAMS data is used to calculate the SO₂ chemistry. Sensitivity experiments explore the sensitivity to changes in OH, H₂O₂, DMS, cloud water, cloud pH value and in the driving analysis data. Input parameters were varied and their differences have been explored. The effect of El Nino and La Nina on SO₂ transport was investigated. The SO₂ reaching the stratosphere was quantified and the sources in the troposphere were determined. The model’s results were compared to POSIDON Aircraft measurements. 

How to cite: Nalapalu, C. S., Wohltmann, I., Rex, M., and Höpfner, M.: Model calculations of the contribution of tropospheric SO2 to the stratospheric aerosol layer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2643, https://doi.org/10.5194/egusphere-egu23-2643, 2023.

The underwater Hunga Tonga-Hunga Ha’apai volcano erupted in the early hours of 15th January 2022 and injected volcanic gases and aerosols to over 50 km altitude. In this talk, we synthesise satellite, ground-based, in situ and radiosonde observations of the eruption to investigate the emissions, the horizontal and vertical dispersion, and the strength of the stratospheric aerosol and water vapour perturbations in the initial six months after the eruption. The aerosol plume was initially formed of two clouds at 30 and 28  km, mostly composed of submicron-sized sulfate particles, without ash, which is washed out within the first day following the eruption. The large amount of injected water vapour led to a fast conversion of SO2 to sulphate aerosols. We find that the Hunga Tonga-Hunga Ha’apai eruption produced the largest global perturbation of stratospheric aerosols since the Pinatubo eruption in 1991 and the largest perturbation of stratospheric water vapour observed in the satellite era. Then, using offline radiative transfer calculations driven by aerosol and water vapour observations, we quantify the net radiative impact across the two species. Immediately after the eruption, water vapour radiative cooling dominated the local stratospheric heating/cooling rates, producing a spectacular radiatively-driven plume descent of several kilometres. At the top-of-the-atmosphere and surface, volcanic aerosol cooling dominated the radiative forcing during this first dispersion phase. However, after two weeks, due to dilution, water vapour heating started to dominate the top-of-the-atmosphere radiative forcing, leading to a net warming of the climate system. On a longer timescale, sulphate particles, undergoing hygroscopic growth and coagulation, sediment and gradually separate from the moisture anomaly entrained in the ascending branch Brewer–Dobson circulation. This is the first time a warming effect on the climate system has been linked to volcanic eruptions, which usually produce a transient cooling.

How to cite: Sellitto, P., Legras, B., Duchamp, C., Belhadji, R., Carboni, E., Siddans, R., and Kloss, C.: The Hunga Tonga-Hunga Ha’apai stratospheric eruption of 15th January 2022: a global warming volcanic plume?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12992, https://doi.org/10.5194/egusphere-egu23-12992, 2023.

The Hunga Tonga volcanic eruption in January 2022 injected extreme amounts of water vapor (H2O) and a moderate amount of aerosol precursor (SO2) into the Southern Hemisphere (SH) stratosphere. The H2O and aerosol perturbations have persisted and resulted in large-scale SH stratospheric cooling, equatorward shift of the Antarctic polar vortex, and slowing of the Brewer-Dobson circulation associated with a substantial ozone reduction in the SH winter midlatitudes. Chemistry-climate model simulations forced by realistic HTHH inputs of H2O and SO2 reproduce the observed stratospheric cooling, circulation changes and ozone loss, demonstrating the observed behavior is due to the volcanic influences. Furthermore, the combination of aerosol transport to polar latitudes and a cold polar vortex enhances springtime Antarctic ozone loss, consistent with observed polar ozone behavior in 2022.

How to cite: Randel, W., Wang, X., Zhu, Y., and Tilmes, S.: Stratospheric climate anomalies and ozone loss caused by the Hunga Tonga volcanic eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2417, https://doi.org/10.5194/egusphere-egu23-2417, 2023.

Recent research has provided evidence of the self-lofting capacity of smoke aerosols in the stratosphere and their self-confinement by persistent anticyclones (Smoke-Charged Vortices, SCV), prolonging the atmospheric residence time and radiative effects of wildfire emissions. By contrast, the volcanic aerosols - composed mostly of non-absorptive sulphuric acid droplets – were never reported to be subject of dynamical confinement. In this study, we use high-resolution satellite observations from various satellite instruments (TROPOMI, ALADIN, CALIPSO, OMPS-LP and EUMETSAT GNSS-RO) together with high-resolution ECMWF ERA5 reanalysis and meteorological radiosoundings to show that the eruption of Raikoke volcano in June 2019 produced a long-lived stratospheric anticyclone termed Vorticized Volcanic Plume (VVP). The primary VVP structure contained 24% of the total erupted mass of sulphur dioxide, circumnavigated the globe three times, and ascended diabatically by more than 13 km in three months through radiative heating of the confined aerosol plume. We argue that persistent anticyclonic formations act to maintain the volcanic plumes at high concentration thereby providing a high degree of radiative heating and upward thrust to volcanic plumes.

The mechanism of dynamical confinement has important implications for the planetary-scale transport of volcanic emissions, their stratospheric residence time, and atmospheric radiation balance. It also provides a challenge or “out of sample test” for weather and climate models that should be capable of reproducing such dynamical structures.

How to cite: Khaykin, S., de Laat, A. T. J., Godin-Beekmann, S., Hauchecorne, A., and Ratynski, M.: Self-lofting and dynamical confinement of the Raikoke volcanic plume, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6021, https://doi.org/10.5194/egusphere-egu23-6021, 2023.

Recent extreme events associated with forest fires and large volcanic eruptions have demonstrated that dense aerosol clouds in the stratosphere often wraps up as persistent compact structures which rotate as anticyclones and also move vertically. One of these vortices has been observed over 3 months and experienced a 20 km rise. Such observations were made after the 2020 Australian wildfires, the 2017 British Columbia fire and more recently after the 2022 Tonga eruption and a few other cases. For all these events, the link was made with anomalous warming or cooling due to the composition of the clouds. This presentation will summarize the observed events and demonstrate the general characters of the stratospheric aerosol vortices. It will also discuss how they are detected by the weather assimilation systems through their signature in temperature, the conditions of their stability and how they can be reproduced experimentally with simple experimental models. Their impact on the transport of long-lived species will be discussed.

Such structures seem so far proper to the Earth stratosphere and have found analogies nowhere else.

Ref: DOIs: 10.1038/s43247-020-00022-5, 10.5194/acp-21-7113-2021, 10.5194/acp-22-14957-2022

How to cite: Legras, B., Podglajen, A., Duchamp, C., Sellitto, P., Limare, A., Niu, Z., Billant, P., Zeitlin, V., Lapeyre, G., and Plougonven, R.: Dynamics of heated (or cooled) vortices in the stratosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10056, https://doi.org/10.5194/egusphere-egu23-10056, 2023.

The Australian record-breaking bushfires around the turn of the year 2020 generated an unprecedented perturbation of thestratospheric composition through the injection of biomass burning material at relatively high altitudes in the upper-troposphere—lower-stratosphere. Associated with this event, a highly-stable smoke-charged anticyclonic vortex, with horizontal extent as large as about 1000 km, was observed. Due to the solar radiation absorption in this vortex, this structure was observed to rise from the initial ~15 km altitude to altitudes higher than ~35 km [Khaykin et al 2020]. This structure persisted in the stratosphere for about 3 months.

Here we present a detailed analysis of the vertically-resolved ozone fields based on the Infrared Atmospheric Sounding Interferometer (IASI) observations, supported by total column observations at relatively high horizontal resolution with Sentinel 5p TROPOMI (TROPospheric Ozone Monitoring Instrument), associated with the smoke-charged vortex due to the Australian bushfires. A marked ozone mini-hole is found, horizontally and vertically co-located with this smoke structure. The dynamical and/or chemical origin of this ozone mini-hole is briefly discussed. Then, ozone profile information is fed to the LibRadtran/UVSPEC radiative transfer model to estimate the impact of this ozone reduction on surface ultraviolet radiation and the results are critically discussed in terms of the possible impacts on the biosphere

Ref : Khaykin, S., Legras, B., Bucci, S., Sellitto P., Isaksen, L., Tencé, F., Bekki, S., Bourassa, A., Rieger, L., Zawada, D., Jumelet, J., and Godin-Beekmann, S.: The 2019/20 Aus- tralian wildfires generated a persistent smoke-charged vortex rising up to 35km altitude, Commun. Earth Environ. 1, 22, https://doi.org/10.1038/s43247-020-00022-5, 2020.

How to cite: Belhadji, R., Sellitto, P., Eremenko, M., Bucci, S., Minh, N., Dufour, G., and Legras, B.: An ozone mini-hole associated with the record-breaking Australian bushfires 2019-2020: satellite observations and the modelled impact on surface ultraviolet radiation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1246, https://doi.org/10.5194/egusphere-egu23-1246, 2023.

During the SOUTHTRAC mission, which took place in September and November 2019, the German
research aircraft HALO performed several cross sections from the equator to the southern tip of
south America. The flight legs were flown along the coast of Brazil at typical altitudes of 13-14 km.
During the northbound flight on October, 7th 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 strongly elevated NO and NO_y as well as CO₂ and could be attributed to the large fires
in South America during this time. These fires occurred in conjunction with convection over
Argentina and Brazil, which led to efficient vertical transport. Lagrangian and chemical model analysis
confirmed the potential impact of convection and biomass burning to the observed enhancements of
ozone and pollutants.
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. We
estimate an ozone production in the polluted air masses of almost 30%
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., Hans-Christoph, L., Heiko, B., Vera, B., Linda, S., Martin, R., Andreas, Z., and Helmut, Z.: Massive ozone production from South American wild fires observed during SOUTHTRAC, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3544, https://doi.org/10.5194/egusphere-egu23-3544, 2023.

Tropical atmospheric waves often have fine vertical scales that are difficult to resolve in models and cannot easily be observed using existing satellite or ground-based instruments. These waves are known to strongly influence the driving of the quasi-biennial oscillation (QBO), which is an important source of seasonal predictability in the lower stratosphere, and have important interactions with dynamical mechanisms such as the Walker Circulation. As the first Doppler wind lidar in space, Aeolus provides high resolution measurements of wind on a global scale, including in the hard-to-observe upper-troposphere lower-stratosphere (UTLS) region of the atmosphere. It is therefore a uniquely capable platform for studying these phenomena. Here, we sample ERA5 as Aeolus to produce like-for-like comparisons of resolved and observed wind structures, and co-locate measurements with stratospheric superpressure balloon observations from the Strateole-2 campaign. We analyse Kelvin waves and their interaction with the QBO, including the 2019/20 QBO disruption for which a special Aeolus scanning mode was implemented. We also compare our results with wave spectra from outgoing long-wave radiation (OLR) measurements, and highlight how Aeolus and future Doppler wind lidar satellites can deepen our understanding of the tropical UTLS more generally.

How to cite: Banyard, T., Wright, C., Hindley, N., and Bramberger, M.: Longitudinal Variations of Tropical Winds in the UTLS: Aeolus and Strateole measurements of Equatorial Waves and the Walker Circulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10132, https://doi.org/10.5194/egusphere-egu23-10132, 2023.

The European Space Agency's Aeolus satellite mission, launched in 2018, provides global wind profiling using a Doppler lidar instrument ALADIN. In this study, we examined ALADIN’s ability to capture and resolve internal gravity waves (IGWs) in the upper troposphere and lower stratosphere (UTLS). To derive the IGW-induced perturbations in the vertical profiles of ALADIN’s horizontal line-of-sight (HLOS) quasi-zonal wind velocity at ~1 km vertical resolution, we subtract the Aeolus-derived "background" wind profiles from the individual measurements. Through a spectral analysis of these data, we then derive the IGW kinetic energy and dominant vertical wavelength in the UTLS over the entire Aeolus mission lifespan. 

  This study represents the first attempt to reconstruct the global distribution of IGW activity using the global wind information exclusively provided by the Aeolus mission. The analysis reveals the well-known IGW sources such as orography, polar vortex dynamics and tropical convection. Here we focus on the tropical UTLS region, where ALADIN has an extended stratospheric coverage. The analysis reveals a previously undocumented spot of enhanced IGW activity in the UTLS, recurring above the Indian Ocean during Boreal Summer. The IGW activity spot is shown to slowly migrate from eastern Africa to the Pacific maritime continent during the June-December period. 

  The Aeolus-derived distribution and seasonal variation of IGW activity were cross-validated using the global temperature profiling by EUMETSAT radio-occultation (RO) satellites. The RO data were resampled to ALADIN resolution and spectrally analyzed in the same way as it was done for ALADIN wind data. The derived IGW potential energy data confirm the seasonal/zonal variation of IGW activity observed by ALADIN, in particular the eastward migration of the IGW activity hotspot, presumably linked to convection within the MJO (Madden-Julian Oscillation). The results suggest that the interannual variation of the IGW kinetic and potential energies in the UTLS is modulated by the Quasi-Biennial Oscillation, whereas the MJO-related waves can be characterized by shorter vertical wavelengths. 

  Another important finding enabled by the joint analysis of the Aeolus wind and RO temperature data is the evidence for a strong IGW generation by the Smoke-Charged Vortex (SCV) produced by the 2019/20 Australian megafires. Overall, with this study we point out the potential of Aeolus wind profiling to improve our understanding of atmospheric dynamics, particularly in the UTLS region.

How to cite: Ratynski, M., Khaykin, S., Hauchecorne, A., and Alexander, J.: Gravity Waves in the Tropical UTLS: New Insights from Aeolus Wind Profiling Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3280, https://doi.org/10.5194/egusphere-egu23-3280, 2023.

The tropical tropopause layer (TTL) is a sea of vertical motions. Convectively-generated gravity waves create vertical winds on scales of a few to 1000s of kilometers as they propagate in a stable atmosphere. Turbulence from gravity wave breaking, radiatively-driven convection and Kelvin-Helmholtz instabilities stirs up the TTL on the kilometer scale. TTL cirrus, which moderate the water vapor concentration in the TTL and stratosphere, form in the cold phases of large-scale (> 100 km) wave activity. It has been proposed in several modelling studies that small-scale (< 100 km) vertical motions control the ice crystal number concentration (NI) and the dehydration efficiency of TTL cirrus. Here, we present the first observational evidence for this.

We use 20 Hz data from the National Aeronautics and Space Administration (NASA) Airborne Tropical TRopopause Experiment (ATTREX) campaign to quantify small-scale vertical wind variability in the TTL and examine its influence on TTL cirrus microphysics. We develop an algorithm to classify turbulence, and long wavelength (5 km < λ < 100 km) and short wavelength (λ < 5 km) gravity wave activity, during level flight legs of at least 100 km. The most commonly sampled conditions are: 1) a quiescent atmosphere with negligible small-scale vertical wind variability, 2) long wavelength gravity wave activity (LWGWA), and 3) LWGWA with turbulence. Turbulence rarely occurs in the absence of gravity wave activity. Cirrus with NI exceeding 10 per liter are rare in a quiescent atmosphere, but about 25 times more likely when there is gravity wave activity and 50 times more likely when there is also turbulence, confirming the results of the aforementioned modeling studies.

Our observational analysis shows that small-scale gravity waves strongly influence NI within TTL cirrus. Global storm-resolving models have recently been run with horizontal grid spacings between 1 and 10 km, sufficient to resolve some small-scale gravity wave activity. We use ATTREX observations to evaluate simulated small-scale (10-100 km) vertical wind power spectra from four global-storm resolving simulations from DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) that have horizontal grid spacings of 3–5 km. We find that all four models have too little resolved vertical wind at horizontal wavelengths less than 100 km, although the bias is much less pronounced in global SAM than in the other models. We expect that deficient small-scale gravity wave activity significantly limits the realism of simulated ice microphysics in these models.

How to cite: Atlas, R. and Bretherton, C.: Aircraft observations of gravity wave activity and turbulence in the tropical tropopause layer: prevalence, influence on cirrus and comparison with global-storm resolving models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3442, https://doi.org/10.5194/egusphere-egu23-3442, 2023.

How to cite: Chau, C. H., Hoor, P., and Tost, H.: Simulated mixing in the upper troposphere by small-scale turbulence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2762, https://doi.org/10.5194/egusphere-egu23-2762, 2023.

The existence of the extratropical transition layer (ExTL) still lacks a physical process based explanation. It is yet an empirical finding based on the observed gradient changes of species within the lowermost stratosphere (LMS). The trace gas distribution directly results from localized and transient dynamical processes in the tropopause region. However, up to this point a dynamic- or process based definition of the ExTL remains an open research question, to large parts due to limitations of the available model and measurement data and resulting uncertainties in the assessment of the relevance of individual processes.

We present a synopsis of a series of recent research studies, which provide strong indications that tropopause-based wind shear and resulting dynamic instability is the key process for the formation of the ExTL. For this we use a multitude of different model and observational data sets, thus addressing the formation and maintenance of the ExTL from the chemical view, the process based dynamical view as well as from the large scale synoptics:

• Process studies identify dynamic instability and turbulent cross-tropopause mixing based on trace gas measurements within distinct mesoscale layers of exceptional wind shear at the tropopause.

• The analysis of several years of ECMWF ERA5 reanalysis data shows that these vertically confined transient layers of intense shear are a frequently occurring global scale feature, which is forced by the underlying large scale tropospheric dynamics.

• The significance of this wind shear layer as a persistent source for dynamic instability and turbulent breakdown of the flow at the tropopause is validated with several years of operational EDR turbulence measurements from commercial aircraft.

How to cite: Kaluza, T., Hoor, P., and Kunkel, D.: A process based definition of the extratropical transition layer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13833, https://doi.org/10.5194/egusphere-egu23-13833, 2023.

Definition of the tropopause has remained a focus of atmospheric science since its discovery near the beginning of the twentieth century. An accurate identification of the tropopause is a vital component to upper troposphere and lower stratosphere research, especially for studies that seek to assess and quantify the two-way exchange of air across the tropopause, which in turn impacts our understanding and prediction of Earth’s radiation budget and climate. Few universal definitions (those that can be reliably applied globally and to both common observations and numerical model output) exist and many definitions with unique limitations have been developed over the years. The most commonly used universal definition of the tropopause is the temperature lapse-rate definition established by the World Meteorological Organization (WMO) in 1957 (the LRT). Despite its widespread use, there are recurrent situations where the LRT definition fails to reliably identify the tropopause. Motivated by increased availability of coincident observations of stability and composition, we reexamine the relationship between stability and composition change in the tropopause transition layer and identify areas for improvement in a stability-based definition of the tropopause. Six locations with long-term (up to 40+ years) balloon observations of temperature, ozone, and water vapor were selected for analysis to offer a variety of environments, including tropical, subtropical, extratropical, and polar environments. Data from these sites are then used to identify covariability between several metrics of atmospheric stability and composition. We show that the vertical gradient of potential temperature is a superior stability metric to identify the greatest composition change in the tropopause transition layer, which we use to propose a new universally applicable potential temperature gradient tropopause (PTGT) definition. A comparison of the PTGT and LRT applied to both observations and reanalysis output will be shown. Overall, our results reveal that the PTGT largely agrees with the LRT, but more reliably identifies tropopause-level composition change when the two definitions differ greatly.

How to cite: Tinney, E., Homeyer, C., Elizalde, L., Hurst, D., Thompson, A., Stauffer, R., Vömel, H., and Selkirk, H.: A Modern Approach to a Stability-Based Definition of the Tropopause, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9439, https://doi.org/10.5194/egusphere-egu23-9439, 2023.

The South-East Asian boundary layer has become one of the most polluted regions in recent years due to rapid
economic growth, which even affect the trace gas composition in the southern hemisphere by inter-hemispheric transport. We
study the transport from the boundary layer of the Asian summer monsoon (ASM) region [15^◦ N, 45^◦ N, 30^◦ E, 120^◦ E] into
the global upper troposphere and lower stratosphere (UTLS) using the Lagrangian chemistry transport model CLaMS driven
by the ERA5 reanalysis during 2010-2014. In particular, we quantify the inter-hemispheric transport contribution from the
ASM region to the southern hemisphere polar region (SP) [60^◦ S, 90^◦ S] and investigate the influence on pollution. Despite the
smaller size of ASM area compared to the southern hemisphere (SH) subtropics [15^◦ S, 45^◦ S] and tropics [15^◦ S, 15^◦ N], we
find that the air mass fractions (AMF) from the ASM to the SP are about 1.5 times larger than the corresponding contributions
from the SH subtropics and about two times smaller than those from the tropics. Transport from the ASM boundary layer to
the Southern polar vortex occurs largely above about 450 K and on timescales longer than 2 years, while transport timescales
to the Antarctic region below the vortex are shorter than about 2 years. The transport contribution from the ASM region to
the SP presents distinct inter-annual variability, which is strongly related to the strength of polar vortex. The relatively young
(less than two years) tracers originating from the ASM region show good correlations with CCl₄, F12, and CH₃Cl observations
from ACE-FTS in the antarctic UTLS. The reconstructed SF₆ indicates that about 20% of SF₆ in the SP stratosphere originates
from the ASM boundary layer, which is larger than the SF₆ fraction of SH subtropical origin, while 50% of SF₆ in the SP
stratosphere originates from the tropical boundary layer.

How to cite: Yan, X., Konopka, P., Ploeger, F., and Podglajen, A.: Interhemispheric transport into the southern hemisphere polar stratosphere from the Asian monsoon region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1348, https://doi.org/10.5194/egusphere-egu23-1348, 2023.

In response to global warming, ozone is predicted to increase aloft due to stratospheric cooling but decrease in the tropical lower stratosphere. The ozone reductions have been primarily attributed to a strengthening Brewer-Dobson circulation, which upwells ozone-poor air. Yet, we find that strengthening upwelling only explains part of the reduction. The reduction is also driven by tropospheric expansion under global warming, which erodes the ozone layer from below, the low ozone anomalies from which are advected upwards. Strengthening upwelling and tropospheric expansion are correlated under global warming, making it challenging to disentangle their relative contributions. Therefore, chemistry-climate model output is used to validate an idealized model of ozone photochemistry and transport with a tropopause lower boundary condition. In our idealized decomposition, strengthening upwelling and tropospheric expansion both contribute at leading order to reducing tropical ozone. Tropospheric expansion leads to an upward shift in the tropospheric destruction of ozone—not to an upward shift in ozone itself—implying that tropopause-following coordinates do not generally remove the effects of tropospheric expansion on ozone.

How to cite: Match, A. and Gerber, E.: Revisiting the stratospheric ozone response to global warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3674, https://doi.org/10.5194/egusphere-egu23-3674, 2023.

The very low temperatures in the tropical tropopause layer (TTL) restrict the moisture entering the stratosphere, leading to its dryness. Whereas the water vapor flux into the stratosphere can be described via the cold point temperatures, our knowledge on the contribution of frozen moisture to the total flux is incomplete. This raises concerns regarding the ability of General Circulation Models (GCMs) to accurately predict changes in total stratospheric moisture following perturbations in the radiative budget due to volcanic aerosol or stratospheric geoengineering, as GCMs  heavily rely on convective parameterizations. The emerging cloud-resolving simulations, however, offer the unprecedented possibility to gain insight into the sensitivity of a TTL, which is not strongly constrained by parameterized convection. Here we present the first results using global convection-resolving simulations to investigate the sensitivity of moisture fluxes within the TTL to an additional heating source. We address the question of how the partitioning of moisture fluxes into water vapor and frozen hydrometeors changes under perturbations. 
This study shows an exceptional resilience of the TTL, keeping the flux partitioning constant - even at an average cold-point warming exceeding 8 K. In the perturbed and unperturbed simulation, frozen moisture contributes around 20 % of the moisture flux into the stratosphere.

How to cite: Kroll, C., Fueglistaler, S., Kornblueh, L., Schmidt, H., and Timmreck, C.: The Sensitivity of Moisture Fluxes into the Tropical Tropopause Layer to External Forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11640, https://doi.org/10.5194/egusphere-egu23-11640, 2023.

Future increases in stratospheric water vapour (SWV) risk amplifying climate change and slowing down the recovery of the ozone layer. However, state-of-the-art climate models strongly disagree on the magnitude of these increases under global warming^1,2. Uncertainty primarily arises from the challenges inherent in modelling the many complex processes leading to dehydration of air during its tropical ascent into the stratosphere³. Here we derive an observational constraint on this longstanding uncertainty factor in Earth's climate change response. Following a statistical learning approach^4,5, we infer historical co-variations between the UTLS temperature structure and tropical lower SWV concentrations. For climate models, we demonstrate that these historically constrained relationships are also highly predictive of the SWV response under strong 4xCO₂ forcing. By extension, we obtain an observationally constrained range for concentration changes per degree of global warming of 0.31±0.39 ppmv K^-1 (90% confidence interval). Our constraint represents a 50% decrease in the 95^th percentile of the climate model uncertainty distribution, which has major implications for surface warming, ozone recovery, and the tropospheric circulation response under climate change.

Across 61 climate models from the 5^th and 6^th phases of the Coupled Model Intercomparison Project (CMIP), we therefore find that a large fraction of future model projections is inconsistent with observational evidence. In particular, frequently projected strong increases (>1 ppmv K^-1) are highly unlikely. We further demonstrate that our constraint on tropical lower SWV can be translated into also reduced uncertainty in the radiative SWV feedback (by 0.05 W m^-2 K^-1). This uncertainty reduction is comparable in size to the overall feedback responses in biogenic volatile organic compounds (BVOCs) or ozone⁶, and is thus of great relevance for policymakers.

References:

[1] Gettelman, A. et al. Multimodel assessment of the upper troposphere and lower stratosphere: Tropics and global trends. Journal of Geophysical Research 115, D00M08 (2010), https://doi.org/10.1029/2009JD013638.

[2] Keeble, J. et al. Evaluating stratospheric ozone and water vapour changes in CMIP6 models from 1850 to 2100. Atmospheric Chemistry and Physics 21, 5015–5061 (2021), https://doi.org/10.5194/acp-21-5015-2021.

[3] Fueglistaler, S. et al. Tropical tropopause layer. Reviews of Geophysics 47, RG1004 (2009), https://doi.org/10.1029/2008RG000267.

[4] Ceppi, P. and Nowack, P. Observational evidence that cloud feedback amplifies global warming. PNAS 118, e2026290118 (2021), https://doi.org/10.1073/pnas.2026290118.

[5] Nowack, P. et al. Using machine learning to build temperature-based ozone parameterizations for climate sensitivity simulations. Environmental Research Letters 13, 104016 (2018), https://doi.org/10.1088/1748-9326/aae2be.

[6] Szopa, S. et al. Short-lived climate forcers. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK and New York, USA, 817–922 (2021).

How to cite: Nowack, P., Ceppi, P., Davis, S., Chiodo, G., Ball, W., Diallo, M. A., Hassler, B., Jia, Y., Keeble, J., and Joshi, M.: An observational constraint on the uncertainty in stratospheric water vapour projections, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2943, https://doi.org/10.5194/egusphere-egu23-2943, 2023.

Water vapor is an essential component for regulating the Earth's radiation budget. To realistically determine the global radiation budget, an accurate description of the water vapor distribution in the upper troposphere and lower stratosphere (UTLS) is therefore indispensable. For example, small changes in water vapor concentration can lead to significant changes in local radiative forcing, especially in the dry lower stratosphere. The change in this region can be even stronger if condensed water in the form of ice clouds is present instead of solely water vapor.

The formation and evolution of ice clouds is crucially determined by the saturation ratio over ice (Si). Ice crystals can only form (and grow) at supersaturated conditions (i.e. Si>1), i.e. in so-called ice supersaturated regions (ISSRs), which also constitute potential regions for the formation and existence of persistent aircraft contrails. Knowing and precisely forecasting the occurrence of ISSRs can help reducing the contribution of aviation to man-made climate change, as contrails usually have a warming effect on the climate.

Ice supersaturation is often observed in the UTLS. However, despite their importance, the large-scale three-dimensional structure of ISSRs is widely unknown. Therefore, we present a three-dimensional climatology of ice supersaturation in the UTLS over the North Atlantic for the years 2010 to 2019. This climatology is based on the recent ERA5 reanalysis data set of the European Center for Medium Weather Forecast (ECMWF), which explicitly allows ice supersaturation in cloud-free conditions. To quantify the quality of the ERA5 data set with respect to ice supersaturation, we use the long-term in-situ measurements of the European Research Infrastructure ’In-service Aircraft for a Global Observing System’ (IAGOS; www.iagos.org) (Petzold et al., 2015).

How to cite: Brast, N., Li, Y., Rohs, S., Konjari, P., Rolf, C., Krämer, M., Petzold, A., Spichtinger, P., and Reutter, P.: 3D climatology of ice supersaturated regions over the North Atlantic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6439, https://doi.org/10.5194/egusphere-egu23-6439, 2023.

The campaign Chemistry of the Atmosphere Field Experiment (CAFE) Brazil was conducted in the Amazon rainforest in December 2022 and January 2023 to study new particle formation in the outflow of convective systems over the Amazon rainforest. In the framework of this campaign, photochemical and aerosol processes in the tropical troposphere were investigated at different altitudes from the boundary layer up to 14 km using the High Altitude and Long Range Research Aircraft (HALO).

The HydrOxyl Radical measurement Unit based on fluorescence Spectroscopy (HORUS) measures the OH and HO₂ abundances as a highly relevant tracer for photochemical and aerosol processes in the tropical troposphere and new particle formation. The Hydroxyl radical (OH) oxidizes trace gases transported by convective systems from the boundary layer into the upper troposphere, leading to the formation of condensable matter. Contrasting conditions were measured, from pristine rainforest to polluted biomass burning and pollution conditions, and the occurrence of HO_x during the day and nighttime in the outflow of electrified and non-electrified convective systems.
The first results of these measurements will be presented, providing unique insights into the air chemistry and lifecycle of aerosols and clouds in the Amazon rainforest.

How to cite: Holzbeck, P., Sreekumar, S., Tsokankunku, A., Marno, D., Rohloff, R., Martinez, M., Nussbaumer, C., Fischer, H., Curtius, J., Pöhlker, M., Lelieveld, J., and Harder, H.: Hydroxyl radicals in the Amazon tropical troposphere measured during the CAFE-Brazil field campaign with HORUS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10355, https://doi.org/10.5194/egusphere-egu23-10355, 2023.