The session will cover all aspects of polar stratospheric ozone, other species in the polar regions as well as all aspects of polar stratospheric clouds. Special emphasis is given to results from recent polar campaigns, including observational and model studies.

We encourage contributions on chemistry, microphysics, radiation, dynamics, small and large scale transport phenomena, mesoscale processes and polar-midlatitudinal exchange. In particular, we encourage contributions on ClOx/BrOx chemistry, chlorine activation, NAT nucleation mechanisms and on transport and mixing of processed air to lower latitudes.

We welcome contributions on polar aspects of ozone/climate interactions, including empirical analyses and coupled chemistry/climate model results and coupling between tropospheric climate patterns and high latitude ozone as well as representation of the polar vortex and polar stratospheric ozone loss in global climate models.

We particularly encourage contributions from the polar airborne field campaigns as e.g. the POLSTRACC (Polar Stratosphere in a Changing Climate) and SouthTRAC (Southern Hemisphere - Transport Composition Dynamics) campaign as well as related activities, which aim at providing new scientific knowledge on the Arctic/Antarctic lowermost stratosphere and upper troposphere in a changing climate. Contributions from WMO's Global Atmosphere Watch (GAW) Programme and from the Network for the Detection of Atmospheric Composition Change (NDACC) are also encouraged.

Convener: Farahnaz Khosrawi | Co-conveners: Hideaki Nakajima, Michael Pitts, Ines TritscherECSECS
| Attendance Mon, 04 May, 10:45–12:30 (CEST)

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Chat time: Monday, 4 May 2020, 10:45–12:30

Chairperson: Farahnaz Khosrawi, Ines Tritscher
D3605 |
Hideaki Nakajima, Isao Murata, Yoshihiro Nagahama, Hideharu Akiyoshi, Takeshi Kinase, Yoshihiro Tomikawa, and Nicholas Jones

We retrieved lower stratospheric vertical profiles of O3, HNO3, and HCl from solar spectra taken with a ground-based Fourier-Transform infrared spectrometer (FTIR) installed at Syowa Station, Antarctica (69.0°S, 39.6°E) from March to December 2007 and September to November 2011.  This was the first continuous measurements of chlorine species throughout the ozone hole period from the ground in Antarctica.  We analyzed temporal variation of these species combined with ClO, HCl, and HNO3 data taken with the Aura/MLS (Microwave Limb Sounder) satellite sensor, and ClONO2 data taken with the Envisat/MIPAS (The Michelson Interferometer for Passive Atmospheric Sounding) satellite sensor at 18 and 22 km over Syowa Station.  HCl and ClONO2 decrease occurred from the end of May at both 18 and 22 km, and eventually in early winter, both HCl and ClONO2 were almost depleted.  When the sun returned to Antarctica in spring, enhancement of ClO and gradual O3 destruction were observed.  During the ClO enhanced period, negative correlation between ClO and ClONO2 was observed in the time-series of the data at Syowa Station.  This negative correlation was associated with the relative distance between Syowa Station and the edge of the polar vortex.  We used MIROC3.2 Chemistry-Climate Model (CCM) results to investigate the behavior of whole chlorine and related species inside the polar vortex and the boundary region in more detail.  From CCM model results, rapid conversion of chlorine reservoir species (HCl and ClONO2) into Cl2, gradual conversion of Cl2 into Cl2O2, increase of HOCl in winter period, increase of ClO when sunlight became available, and conversion of ClO into HCl, was successfully reproduced.  HCl decrease in the winter polar vortex core continued to occur due to both transport of ClONO2 from the subpolar region to higher latitudes, providing a flux of ClONO2 from more sunlit latitudes into the polar vortex, and the heterogeneous reaction of HCl with HOCl.  Temporal variation of chlorine species over Syowa Station was affected by both heterogeneous chemistries related to Polar Stratospheric Cloud (PSC) occurrence inside the polar vortex, and transport of a NOx-rich airmass from the polar vortex boundary region which can produce additional ClONO2 by reaction of ClO with NO2.  The deactivation pathways from active chlorine into reservoir species (HCl and/or ClONO2) were confirmed to be highly dependent on the availability of ambient O3.  At 18 km where most ozone was depleted, most ClO was converted to HCl.  At 22km where some O3 was available, additional increase of ClONO2 from pre-winter value occurred, similar as in the Arctic.

How to cite: Nakajima, H., Murata, I., Nagahama, Y., Akiyoshi, H., Kinase, T., Tomikawa, Y., and Jones, N.: Chlorine partitioning near the polar vortex edge observed with ground-based FTIR and satellites at Syowa Station, Antarctica in 2007 and 2011, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2280, https://doi.org/10.5194/egusphere-egu2020-2280, 2020.

D3606 |
Michael Weimer, Jennifer Schröter, Lars Hoffmann, Oliver Kirner, Roland Ruhnke, and Peter Braesicke

Polar Stratospheric Clouds (PSCs) play a key role in explaining ozone depletion on large
scales as well as on regional scales. Mountain waves can be formed in the lee of a mountain
in a stably stratified atmosphere. They can propagate upwards into the stratosphere and
induce temperature changes in the order of 10 to 15 K. Thus, large PSCs localised around the
mountain ridge can be formed, leading to increased chlorine activation and subsequently to
a larger ozone depletion. It was estimated that 30 % of the southern hemispheric PSCs can
be explained by mountain waves. However, for the direct simulation of mountain-wave
induced PSCs, the mountains have to be represented adequately in global chemistry climate
models which was a challenge in the past due to too low horizontal resolution.

The ICOsahedral Nonhydrostatic (ICON) modelling framework with its extension for Aerosols
and Reactive Trace gases (ART) includes a PSC scheme coupled to the atmospheric chemistry
in the model. The PSC scheme calculates the formation of all three PSC types independently
resulting in the calculation of the heterogeneous reaction rates of chlorine and bromine
species on the surface of PSCs. ICON-ART provides the possibility of local grid refinement
with two-way interaction. With this, the grid around a mountain can be refined so that
mountain waves can be directly simulated in this region with a feedback to the coarser
global resolution.

In this study, we show the formation of mountain-wave induced PSCs with ICON-ART for the
example of a mountain wave event in July 2008 around the Antarctic Peninsula. It is
evaluated with satellite measurements of AIRS and CALIOP and its impact on chlorine and
bromine activation as well as on the ozone depletion in the southern hemisphere are
analysed. We demonstrate that the effect of mountain-wave induced PSCs can be
represented in the coarser global grid by using local grid refinement with two-way
interaction. Thus, this study bridges the gap between directly simulated mountain-wave
induced PSCs and their representation in a global simulation.

How to cite: Weimer, M., Schröter, J., Hoffmann, L., Kirner, O., Ruhnke, R., and Braesicke, P.: Mountain-wave Induced Polar Stratospheric Clouds with ICON-ART: An Example at the Antarctic Peninsula, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2451, https://doi.org/10.5194/egusphere-egu2020-2451, 2020.

D3607 |
| Highlight
Florence Goutail, Jean-Pierre Pommereau, Andrea Pazmino, Franck Lefevre, Cathy Clerbaux, Anne Boynard, Juliette Hadji-Lazaro, Martyn Chipperfield, Wuhu Feng, Michel Van Roozendael, Nis Jepsen, Georg Hansen, Rigel Kivi, Kristof Bognar, Kimberly Strong, and Kaley Walker

The amplitude of ozone depletion in the Arctic is monitored every year since 1990 by comparison between total ozone measurements of SAOZ / NDACC UV-Vis spectrometers deployed in the Arctic and 3-D chemical transport model simulations in which ozone is considered as a passive tracer.

When SAOZ measurements are missing for various reasons, lack of sunlight, station closed or instrument failure, they are replaced since 2017 by IASI/Metop overpasses above the station. These measurements in the thermal Infrared are available all year around, at all latitudes even in the polar night. IASI data have been compared to SAOZ and to 3-D CTM REPROBUS and the agreement is better than 3% at the latitude of the polar circle.

The method allows determining the evolution of the daily rate of the ozone destruction and the amplitude of the cumulative loss at the end of the winter. The amplitude of the destruction varies between 0-10% in relatively warm and short vortex duration years up to 25-39% in colder and longer ones.

Since a strong and large vortex centred at the North Pole, PSCs and activated chlorine are still present at all levels in the lower stratosphere on January 9, 2020, there is a good probability that a significant O3 loss may happen in 2020. But since, as shown by the unprecedented depletion of 39% in 2010/11, the loss depends on the vortex duration, strength and possible re-noxification, it is difficult to predict in advance the amplitude of the cumulative loss at the end of the winter.

Shown in this presentation will be the evolution of ozone loss and re-noxification in the Arctic vortex during the winter 2019/20 compared to previous winters and REPROBUS and SLIMCAT CTM simulations.

How to cite: Goutail, F., Pommereau, J.-P., Pazmino, A., Lefevre, F., Clerbaux, C., Boynard, A., Hadji-Lazaro, J., Chipperfield, M., Feng, W., Van Roozendael, M., Jepsen, N., Hansen, G., Kivi, R., Bognar, K., Strong, K., and Walker, K.: Total ozone loss during the 2019/20 Arctic winter and comparison to previous years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3571, https://doi.org/10.5194/egusphere-egu2020-3571, 2020.

D3608 |
| Highlight
Michael Pitts and Lamont Poole

Even though the role of polar stratospheric clouds (PSCs) in stratospheric ozone depletion is well established, important questions remain unanswered that have limited our understanding of PSC processes and how to accurately represent them in global models.  This has called into question our prognostic capabilities for future ozone loss in a changing climate.  A more complete picture of PSC processes on polar vortex-wide scales has emerged from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) instrument on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite that has been observing PSCs at latitudes up to 82 degrees in both hemispheres since June 2006.  In this paper, we present a state-of-the-art climatology of PSC spatial and temporal distributions and particle composition constructed from the more than 14-year CALIOP spaceborne lidar dataset.  The climatology also includes estimates of particulate surface area density and volume density to facilitate comparisons with in situ data and measurements by other remote sensors, as well as with theoretical models relating PSCs to heterogeneous chemical processing and ozone loss. Finally, we compare the CALIOP PSC data record with the 1979-1989 SAM II (Stratospheric Aerosol Measurement II) solar occultation PSC record to investigate possible multi-decadal changes in PSC occurrence.

How to cite: Pitts, M. and Poole, L.: CALIOP PSC observations from 2006-2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3969, https://doi.org/10.5194/egusphere-egu2020-3969, 2020.

D3609 |
Ohad Harari, Chaim Garfinkel, and Shlomi Ziskin

The Northern Hemisphere and tropical circulation response to interannual variability in Arctic stratospheric ozone is analyzed in a set of the latest model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project. All models simulate a connection between ozone variability and temperature/geopotential height in the lower stratosphere similar to that observed. A connection between Arctic ozone variability and polar cap surface air pressure is also found, but additional statistical analysis suggests that it is mediated by the dynamical variability that typically drives the anomalous ozone concentrations. While the CCMI models also show a connection between Arctic stratospheric ozone and the El Niño–Southern Oscillation (ENSO), with Arctic stratospheric ozone variability leading to ENSO variability 1 to 2 years later, this relationship in the models is much weaker than observed and is likely related to ENSO autocorrelation rather than any forced response to ozone. Overall, Arctic stratospheric ozone is related to lower stratospheric variability. Arctic stratospheric ozone may also influence the surface in both polar and tropical latitudes, though ozone is likely not the proximate cause of these impacts and these impacts can be masked by internal variability if data are only available for years.

Harari, O., Garfinkel, C. I., Ziskin Ziv, S., Morgenstern, O., Zeng, G., Tilmes, S., Kinnison, D., Deushi, M., Jöckel, P., Pozzer, A., O'Connor, F. M., and Davis, S.: Influence of Arctic stratospheric ozone on surface climate in CCMI models, Atmos. Chem. Phys., 19, 9253–9268, https://doi.org/10.5194/acp-19-9253-2019, 2019.

How to cite: Harari, O., Garfinkel, C., and Ziskin, S.: Influence of Arctic stratospheric ozone on surface climate in CCMI models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5086, https://doi.org/10.5194/egusphere-egu2020-5086, 2020.

D3610 |
Kaley Walker, Kimberly Strong, Pierre Fogal, and James R. Drummond

Ground-based measurements provide critical data to validate satellite retrievals of atmospheric trace gases and to assess the long-term stability of these measurements.  As of February 2020, the Canadian-led Atmospheric Chemistry Experiment (ACE) satellite mission has been making measurements of the Earth's atmosphere for nearly sixteen years and Canada's Optical Spectrograph and InfraRed Imager System (OSIRIS) instrument on the Odin satellite has been operating for over sixteen years.  As ACE and OSIRIS continue to operate far beyond their planned two-year missions, there is an ongoing need to validate the trace gas profiles from the ACE-Fourier Transform Spectrometer (ACE-FTS), the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) and OSIRIS.  In particular, validation comparisons are needed during Arctic springtime to understand better the measurements of species involved in stratospheric ozone chemistry.

To this end, seventeen Canadian Arctic ACE/OSIRIS Validation Campaigns have been conducted during the spring period (February - April in 2004 - 2020) at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut (80N, 86W). For more than a decade, these campaigns have been undertaken in collaboration with the Canadian Network for the Detection of Atmospheric Change (CANDAC). The spring period coincides with the most chemically active time of year in the Arctic, as well as a significant number of satellite overpasses. A suite of as many as 13 ground-based instruments, as well as frequent balloon-borne ozonesonde and radiosonde launches, have been used in each campaign. These instruments include: a ground-based version of the ACE-FTS (PARIS - Portable Atmospheric Research Interferometric Spectrometer), a terrestrial version of the ACE-MAESTRO, a SunPhotoSpectrometer, two CANDAC zenith-viewing UV-visible grating spectrometers, a Bomem DA8 Fourier transform spectrometer, the CANDAC Bruker 125HR Fourier transform spectrometer, an EM27/SUN Fourier transform spectrometer, a Systeme d’Analyse par Observations Zenithales (SAOZ) instrument, a Pandora spectrometer, and several Brewer spectrophotometers. In the past several years, these results have been used to validate the measurements by the ACE-FTS, ACE-MAESTRO, and OSIRIS instruments as well as the TANSO-FTS instrument on the Japanese Greenhouse Gases Observing Satellite (GOSAT) and the TROPOMI instrument on the Sentinel 5 Precursor. This presentation will focus on an overview of the measurements made by the ground-based, balloon-borne and satellite-borne instruments during the recent ACE/OSIRIS Arctic Validation campaigns and highlight how these have been used for satellite validation.

How to cite: Walker, K., Strong, K., Fogal, P., and Drummond, J. R.: Seventeen Years of the Canadian Arctic ACE/OSIRIS Validation Project at PEARL, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6303, https://doi.org/10.5194/egusphere-egu2020-6303, 2020.

D3611 |
Rocco Sedona, Lars Hoffmann, Reinhold Spang, Gabriele Cavallaro, Sabine Griessbach, Michael Höpfner, Matthias Book, and Morris Riedel

Polar stratospheric clouds (PSC) play a key role in polar ozone depletion in the stratosphere. Improved observations and continuous monitoring of PSCs can help to validate and enhance chemistry-climate models that are used to predict the evolution of the polar ozone hole. Here we present the results of our study in which we explored the potential of applying machine learning (ML) methods to classify PSC observations of infrared limb sounders. Two datasets have been considered. The first dataset is a collection of infrared spectra captured in Northern Hemisphere winter 2006/2007 and Southern Hemisphere winter 2009 by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument onboard ESA's Envisat satellite. The second dataset is the cloud scenario database (CSDB) of simulated MIPAS spectra. We first performed an initial analysis to assess the basic characteristics of these datasets and to decide which features to extract from them. More than 10,000 Brightness temperature differences (BTDs) features have been generated and fed as input to the ML methods instead of directly using the infrared spectra. Next, we assessed the use of ML methods for the reduction of the dimensionality of this large feature space using principal component analysis (PCA) and kernel principal component analysis (KPCA) as well as the classification with the random forest (RF) and support vector machine (SVM) techniques. All methods were found to be suitable to retrieve information on the composition of PSCs. Of these, RF seems to be the most promising method, being less prone to overfitting and producing results that agree well with established results based on conventional classification methods.

How to cite: Sedona, R., Hoffmann, L., Spang, R., Cavallaro, G., Griessbach, S., Höpfner, M., Book, M., and Riedel, M.: Using machine learning method to classify polar stratospheric cloud types from Envisat MIPAS observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8103, https://doi.org/10.5194/egusphere-egu2020-8103, 2020.

D3612 |
Wuhu Feng, Martyn Chipperfield, Sandip Dhmose, Florence Goutail, Michelle Santee, Benni Birner, Ralph Keeling, and Gabriele Stiller

Three-dimensional chemical transport models (CTMs) have been widely used in a wide variety of scientific studies (e.g., to obtain a better understanding of tracer transport and to study the dynamical and chemical processes which control polar ozone losses etc). However, there are still some uncertainties in the model simulations and indeed in our understanding. For example, the accuracy of ozone simulations largely depends on the transport, chemistry and treatment of PSCs in the model as well as the forcing files. 

Here we have used a  CTM model TOMCAT/SLIMCAT with a detailed description of stratospheric and tropospheric chemistry forced by differnt wind fields (ECMWF ERA-Interim and ERA5 reanalysis datasets) to investigate the different dynamical fields on the simulated tracer transport, ozone and other chemical species. Both simulations have been run from 1979 to 2018. First we will assess the impact of different reanalysis data on the idealised tracers when the model includes additional process of the gravitational separation of gases (e.g., Ar/N2) and compare the model results with dataset of gravitational fractionation of Ar/N2 and AoA observations made on flask samples from three airborne research projects. Modelled AoA will be also compared with MIPAS data.  Then we will focus on the polar ozone loss from late 1990 to 2018 and quntify
the amount of chemical ozone loss using both models and satellite observations as well as  SAOZ measurements. The year-to-year variation of polar ozone depletion will also be discussed, in particular for the recent years of decreasing stratospheric chlorine loading. 

How to cite: Feng, W., Chipperfield, M., Dhmose, S., Goutail, F., Santee, M., Birner, B., Keeling, R., and Stiller, G.: Impact of ECMWF ERA-Interim and ERA5 reanalysis on the simulated tracer transport and polar ozone loss using a chemical transport model TOMCAT/SLIMCAT, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8918, https://doi.org/10.5194/egusphere-egu2020-8918, 2020.

D3613 |
Davide Putero, Rita Traversi, Angelo Lupi, Francescopiero Calzolari, Maurizio Busetto, Laura Tositti, Stefano Crocchianti, and Paolo Cristofanelli

In this work, eight years (2006–2013) of continuous measurements of near-surface ozone (O3) at the WMO/GAW contributing station “Concordia” (DMC, 75°06’S, 123°20’E, 3280 m a.s.l.) are presented, and the role of specific atmospheric processes in affecting O3 variability is investigated. In particular, during the period of highest data coverage (i.e., 2008–2013), O3 enhancement events (OEEs) were systematically observed at DMC, affecting 11.6% of the dataset. As deduced by a statistical selection methodology, the OEEs are affected by a significant interannual variability, both in the average and in the frequency of O3 values. To explain part of this variability, OEEs were analyzed as a function of: (i) total column of O3 and UV-A irradiance variability, (ii) long-range transport of air masses over the Antarctic plateau (by using LAGRANTO), and (iii) occurrence of “deep” stratospheric intrusion events (by using STEFLUX). The overall O3 concentrations are controlled by a day-to-day variability, which indicates the dominating influence of processes occurring at “synoptic” scales rather than “local” processes. Despite previous studies indicated an inverse relationship between OEEs and TCO, we found that the annual frequency of OEEs was higher when TCO values at DMC were higher than usual. The annual occurrence of OEEs at DMC was also related to the total time spent by air masses over the Antarctic plateau before their arrival at DMC, suggesting that the accumulation of photochemically-produced O3 during the transport dominated the local O3 production. Lastly, the influence of “deep” stratospheric intrusion events at DMC was analyzed, and it was observed that this contribution played only a marginal role (the highest frequency observed was 3% of the period, in November).

This latter point, i.e., the frequency and seasonality of stratosphere-to-troposphere (STE) events, and the relative influence of specific transport mechanisms, as well as snow chemistry, are still under debate. These topics will be investigated in the STEAR (Stratosphere-to-Troposphere Exchange in the Antarctic Region) project, starting in 2020 and funded by the Italian Antarctic Research Program (PNRA). In particular, STEAR will provide an assessment of STE events in Antarctica, by using both continuous observations (e.g., O3 and Beryllium-7) at DMC, and modeling outputs. In addition to DMC measurements, simultaneous atmospheric composition datasets will be analyzed at Antarctic coastal observatories, i.e., the Mario Zucchelli (MZS) and Jang Bogo (JBS) stations.   

How to cite: Putero, D., Traversi, R., Lupi, A., Calzolari, F., Busetto, M., Tositti, L., Crocchianti, S., and Cristofanelli, P.: Analysis of multi-year near-surface ozone observations at the WMO/GAW “Concordia” station, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9630, https://doi.org/10.5194/egusphere-egu2020-9630, 2020.

D3614 |
Gennadi Milinevsky, Asen Grytsai, Oleksandr Evtushevsky, Yury Yampolsky, Andrew Klekociuk, and Yuke Wang

Ozone content in the terrestrial atmosphere is dependent on chemical and dynamical factors including catalytic destruction under the influence of chlorine and bromine, Brewer–Dobson circulation, and large-scale atmospheric waves. The appearance of ozone molecules in the stratosphere is caused by solar ultraviolet radiation as well. Therefore solar activity variations can influence ozone content. The 11-year solar cycle had been earlier identified in the upper stratosphere. Satellite ozone observations were begun from the 1970s are almost continuous from 1979 including the vertical ozone distribution, in particular with the use of Solar Backscattered UltraViolet (SBUV) instruments. These data cover the troposphere and stratosphere layers, from the surface to near 50 km. Vertical ozone distribution over the Ukrainian Antarctic station Akademik Vernadsky (65.25°S, 64.27°W) and in the corresponding latitudinal range 60–65°S is studied in this work with the following analysis of possible solar activity display in other latitudinal belts. Sunspot numbers have been considered as the simplest characteristics of solar activity. We have considered SBUV yearly data paying main attention to the time range from 1979 when the measurements are most reliable. Periodicity in the series of ozone layer content has been studied with use of wavelet transform. Processing of the SBUV data over Vernadsky has shown a dominating period near 10–11 years at the heights 18–31 km. In the troposphere and lower stratosphere, this period is unclear. A similar situation is observed above 31 km indicating the upper altitudinal threshold in the presence of the 10–11-year periodicity in the ozone data. The solar cycle influence on the ozone vertical distribution in the Antarctic region has been studied. From our analysis, the solar cycle plays an important role in the decadal variability of the mid-stratospheric ozone over Vernadsky Station with decrease of the effect both in the troposphere – lower stratosphere and in the upper stratosphere. A similar analysis is also realized for zonal mean ozone at the 60–65°S latitudes belt and for the region of zonal ozone maximum (Casey), where the solar cycle was indicated at the heights 31–37 km. Thus, zonal asymmetry in the heights of the maximum solar cycle effect in the Antarctic ozone exists. Periods close to 11 years are observed in the lower stratosphere of equatorial latitudes exhibiting seasonal dependency. At altitudes, 25–30 km, the southern stratosphere has more evident signs of solar cycle periods than the northern one. The summer upper stratosphere with a high flux of direct solar radiation is also a region with prominent quasi-11 year periods. In sum, three main regions with solar activity influence (tropical lower stratosphere, west Antarctic middle stratosphere, and east Antarctic upper stratosphere) are identified. The asymmetry between solar cycle influence (i) in the northern and southern hemisphere mid-stratosphere and (ii) zonal ozone maximum and minimum over Antarctica is denoted for the first time.

This work was partly supported by the project 19BF051-08 Taras Shevchenko National University of Kyiv and by the International Center of Future Science, Jilin University.

How to cite: Milinevsky, G., Grytsai, A., Evtushevsky, O., Yampolsky, Y., Klekociuk, A., and Wang, Y.: Solar activity influence on the ozone vertical distribution from SBUV data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11367, https://doi.org/10.5194/egusphere-egu2020-11367, 2020.

D3615 |
Christoph Kalicinsky, Sabine Grießbach, and Reinhold Spang

Polar stratospheric clouds (PSCs) have an important influence on the spatial and temporal
evolution of different trace gases, (e.g. ozone, HNO3) in the polar vortex in winter due to direct
and indirect processes (e.g. activation of chlorine, redistribution of HNO3). Thus, the detection
of PSCs and a detailed distinction between the different PSCs types Nitric Acid Trihydrade
(NAT), Supercooled Ternary Solution (STS), and ice are important as they build a basis for
model comparisons to reduce uncertainties in the representation of PSCs in models. Infrared
limb sounder are well suited for this purpose as they enable both, the detection of clouds and
the discrimination between the different types.
The CRISTA-NF instrument, an airborne infrared limb sounder, observed a new spectral fea-
ture during measurements inside PSCs within the RECONCILE aircraft campaign. In contrast
to the previously known feature at 820 cm-1, which has been used in former studies for the
detection of NAT PSCs, the new feature was detected at about 816 cm-1. We performed a
large set of radiative transfer simulations for different PSC situations (varying PSC altitude
and thickness, PSC type, number density and median radius of the particle size distribution)
for the airborne viewing geometry of CRISTA-NF. The simulation results show that under the
assumption of spherical NAT particles the spectral feature transforms from the original feature
at 820 cm-1 to a shifted version (peak shifts to smaller wavenumbers) and finally to a step-like
feature with increasing median radius. Based on this behaviour we defined different colour ra-
tios to detect PSCs containing NAT particles and to subgroup them into three sizes regimes:
small NAT, medium size NAT, and large NAT. In addition, we used the simulation results to
adopt a method, which has been used to detect ice in MIPAS-ENV observations, to the airborne
geometry and to refine the corresponding threshold values.
We applied all methods of cloud detection and type discrimination to the CRISTA-NF observa-
tions during the RECONCILE campaign. The new defined NAT detection method is capable
to detect the shifted NAT feature, which is clearly visible in the radiance spectra.

How to cite: Kalicinsky, C., Grießbach, S., and Spang, R.: Radiative transfer simulations and observations of airborne infrared emission spectra in the presence of PSCs: Detection of clouds and discrimination of cloud types, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13750, https://doi.org/10.5194/egusphere-egu2020-13750, 2020.

D3616 |
Alexander James, Sebastien N. F. Sikora, Mark Holden, Graham W. Mann, John M. C. Plane, and Benjamin J. Murray

Nucleation of crystalline ice and nitric acid hydrates in Polar Stratospheric Clouds (PSC) is important for the destruction of ozone, both through changing the rate of activation of ozone destroying species and through the removal by sedimentation of nitric acid, which can deactivate ozone destroying species. Nucleation is thought to proceed heterogeneously on fragmented meteoric materials, leading to formation of ice and nitric acid trihydrate. The heterogeneous nature of meteoric materials and the potential to form multiple crystalline phases makes this system particularly complex. In particular, the characteristics of meteoric fragments which allow them to nucleate crystallisation in PSCs are unknown. We have investigated the nature of nucleation of nitric acid solutions on meteorite thin section surfaces. We find that nucleation occurs on a range of sites on the surface without significant reproduction in repeat freezing experiments. Electron microscopy showed significant diversity in the type of surface features present in regions where nucleation was observed. This is in contrast to recent studies of ice nucleation on K-feldspar and quartz surfaces, where particular sites were found to dominate nucleation. We also observed a range of different crystalline phases forming competitively, some of which are not represented on the HNO3 / H2O equilibrium phase diagram. The results reinforce the complexity of nucleation in PSC and do not support simplifying assumptions commonly made in the literature e.g. around the order in which phases form. In order to facilitate a predictive capacity of future trends in ozone loss significant work is required in understanding the nucleation of nitric acid hydrates by meteoric material.

How to cite: James, A., Sikora, S. N. F., Holden, M., Mann, G. W., Plane, J. M. C., and Murray, B. J.: What controls nucleation of ice and nitric acid hydrates by meteoric material?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17874, https://doi.org/10.5194/egusphere-egu2020-17874, 2020.

D3617 |
Florent Tencé, Julien Jumelet, Alain Sarkissian, Slimane Bekki, and Philippe Keckhut

Polar Stratospheric Clouds (PSCs) play a primary role in polar stratospheric ozone depletion processes. Aside from recent improvements in both spaceborne PSCs monitoring as well as investigations on PSCs microphysics and modeling, there are still uncertainties associated to solid particle formation and their denitrification potential. In that regard, groundbased instruments deliver detailed and valuable measurements that complement the global spaceborne coverage.

Operated since 1989 at the French antarctic station Dumont d’Urville (DDU) in the frame of the international Network for the Detection of Atmospheric Composition Change (NDACC), the Rayleigh/Mie/Raman lidar provides over the years a solid dataset to feed both process and classification studies, by monitoring cloud and aerosol occurrences in the upper troposphere and lower stratosphere. Located on antarctic shore (66°S - 140°E), the station has a privileged access to polar vortex dynamics. Measurements are weather-dependent with a yearly average of 130 nights of monitoring. Expected PSC formation temperatures are used to evaluate the whole PSC season occurrences.

We hereby present a consolidated dataset from 10 years of lidar measurements using the 532nm backscatter ratio, the aerosol depolarisation and local atmospheric conditions to help in building an aerosol/cloud classification. Using the different PSC classes and associated optical properties thresholds established in the recent PSC CALIOP classification, we build a picture of the 2007-2019 events, from march to october.

Overall, the DDU PSC pattern is very consistent with expected typical temperature controlled microphysical calculations. Outside of background sulfate aerosols and anomalies related to volcanic activity (like in 2015), Supercooled Ternary Solution (STS) particles are the most observed particle type, closely followed by Nitric Acid Trihydrate (NAT). ICE clouds are less but regularly observed. ICE clouds also have to be cleary separated from cirrus clouds, raising the issue of accurate dynamics tropopause calculations.

Validation of the spaceborne measurements as well as multiple signatures of volcanic or even biomass originated aerosol plumes strengthens the need for groundbased monitoring especially in polar regions where instrumental facilities remain sparse.

How to cite: Tencé, F., Jumelet, J., Sarkissian, A., Bekki, S., and Keckhut, P.: 10 years of Polar Stratospheric Clouds lidar measurements at the French antarctic station Dumont d’Urville, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18176, https://doi.org/10.5194/egusphere-egu2020-18176, 2020.

D3618 |
| Highlight
C. Michael Volk, Valentin Lauther, Andrea Rau, Fridolin Hader, and Svetlana Cvetkova

During the recent SouthTRAC (Transport and composition of the Southern Hemisphere UTLS) campaign the German High Altitude and LOng range research aircraft (HALO) intensively probed the bottom of the Antarctic vortex and the adjacent mid to high latitude upper troposphere / lower stratosphere (UTLS) throughout late winter and spring 2019.  A main goal of this mission was to study dynamics, transport and composition of this region, and particularly to assess the impact of the Antarctic vortex on the southern hemisphere UTLS.  The Antarctic winter 2019 was extraordinary with respect to dynamics, with a sudden stratospheric warming (only the second one ever observed) leading to a less stable and unusually warm polar vortex. The campaign consisted of two phases based in Rio Grande, Argentina (54°S) and comprised a total of 27 science flights including transfer flights to/from Argentina and 13 local flights from Rio Grande in September/early October and in November 2019.  A number of these flights penetrated into the lower Antarctic vortex, others crossed streamers or thin filaments shed from the vortex by frequent Rossby wave breaking events.

We present observations obtained on board of HALO by the University of Wuppertal's High Altitude Gas Analyzer –V (HAGAR-V), a 5-channel in-situ tracer instrument recently developed for HALO to study the chemical composition, dynamics, and transport in the UTLS.  HAGAR-V combines i) a fast CO2 measurement by NDIR analyzer (every 3 s), ii) a 2-channel GC/ECD-system measuring the long-lived tracers CFC-12, SF6 (every 40 s), CFC-11, CFC-113 and Halon-1211 (every 80s), and iii) a 2-channel GC/MS system measuring a large suite of further long-lived (e.g. HFCs) and short-lived halogenated tracers, including further chlorine source gases (e.g. CCl4, CH2Cl2, CHCl3, C2Cl4, HCFCs) every 2-4 minutes.  We will discuss the unusually active dynamics and associated tracer transport in the vicinity of the 2019 Antarctic vortex reflected by these measurements, and show the temporal development of vertical distributions and tracer correlations throughout the spring.  We will also compare the tracer distributions during SouthTRAC with those observed from the M55 Geophysica aircraft during the 1999 Antarctic campaign APE-GAIA.

How to cite: Volk, C. M., Lauther, V., Rau, A., Hader, F., and Cvetkova, S.: Airborne in situ tracer observations in the 2019 Springtime Antarctic UTLS during the HALO SouthTRAC campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18407, https://doi.org/10.5194/egusphere-egu2020-18407, 2020.

D3619 |
Quentin Errera, Jonas Debosscher, Emmanuel Dekemper, Philippe Demoulin, Didier Fussen, Didier Piroux, Filip Vanhellemont, and Nina Mateshvili

ALTIUS (Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere) is a satellite mission dedicated to continue Earth limb measurements for atmospheric sciences (Fussen et al., JQSRT, 2019). It is an element of the ESA Earth Watch programme and is expected to be launched in 2024 on a low earth polar orbit. The instrument is based on three spectral imagers that will measure in UV-vis-NIR wavelength range and will operate in different viewing geometry: limb scattering and occultation of the sun, the moon, the planets and the stars. ALTIUS will retrieve vertical profiles of ozone, nitrogen dioxide, aerosol extinction, among others.

In this study, we present an Observing System Simulation Experiment (OSSE) of ALTIUS ozone profiles that we have compared with the existing observations from Aura Microwave Limb Sounder (MLS). For this purpose, we have created a stratospheric ozone reference dataset between June and September 2008 based on the assimilation of MLS data with the Belgian Assimilation System for Chemical Observations (BASCOE). During the MLS assimilation experiment, the ozone state is saved in the space of ALTIUS previously determined with the ALTIUS orbit simulator, then perturbed according to the ALTIUS error budget, which creates ALTIUS synthetic observations. The assimilation of these ALTIUS ozone profiles agrees well with those of MLS. The assimilation of the different modes of ALTIUS reveals that all modes are necessary to constrain ozone during the polar night: solar and stellar occultations are the most constraining during the June-August period while limb scattering profiles are the most constraining from September onward.


How to cite: Errera, Q., Debosscher, J., Dekemper, E., Demoulin, P., Fussen, D., Piroux, D., Vanhellemont, F., and Mateshvili, N.: Observing System Simulation Experiment (OSSE) of future ALTIUS ozone profiles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18952, https://doi.org/10.5194/egusphere-egu2020-18952, 2020.

D3620 |
Edgardo Sepulveda, Raúl Cordero, Alessandro Damiani, and Penny Rowe

The Ozone Mapping and Profiles Suite (OMPS), in orbit since October 2011 as a part of the Suomi National Polar-orbiting Partnership (Suomi NPP) Satellite includes three different spectral instruments for retrieving ozone distributions globally. One of those is the Limb Profiler (LP), which has made measurements since February 2012. The LP retrieves ozone profiles between approximately 12 km and 55 km of height.

Here we compare the OMPS LP version 2.5 ozone profiles with Electrochemical Concentration Cell (ECC) ozonesonde measurements from three Antarctic stations during the period 2012-2019: Marambio Station (-64.2413, -56.6266) on the Antarctic Peninsula, and Syowa Station (-68.3040, 49.6443) and Davis Station (-68.3110, 75.0222) in East Antarctica. The ozonesonde profiles include ozone concentration from the surface to an altitude of about 30 km. Thus, our comparisons are for altitudes of about 12 to 27 km.

During the period of highest ozone concentration (December – April), mean relative differences between OMPS LP and ozonesonde concentration typically change with height, ranging from -10% at 12-17 km altitude to 10% at 27 km altitude with slight variation between the three sites (e.g. Marambio has a higher standard deviation of 35% at 12 km). A mean relative difference of -5% is found for Syowa from about 15 km to 24 km, unlike Marambio and Davis, which have no clear difference at these heights.

Relative differences were also examined in September, when ozone concentrations are significantly lower due to the formation of the ozone hole, except for September 2019, which is excluded because a sudden stratospheric warming effect occurred. A mean relative difference of almost 30% is found in Marambio and Davis from about 12 km to 21 km, with a standard deviation of 100% at 18 km. The mean relative difference at Syowa is similar except that the relative difference peaks at almost 60% at 16 km. Marambio and Davis have similar biases above 21 km (10%), where the bias at Syowa is -5%.

How to cite: Sepulveda, E., Cordero, R., Damiani, A., and Rowe, P.: Comparison of ozone profiles from the Ozone Mapping and Profiles Suite with ozonesonde measurements over Antarctica during 2012-2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19315, https://doi.org/10.5194/egusphere-egu2020-19315, 2020.

D3621 |
Andrew Orr, Scott Hosking, Aymeric Delon, Tracy Moffat-Griffin, Lars Hoffman, Reinhold Spang, Luke Abrahams, James Keeble, and Peter Braesicke

An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves, enabling stratospheric temperatures to fall below the threshold value for PSC formation in the cold phases of these waves even if the synoptic-scale temperatures are too high. However, this formation mechanism is usually missing in chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of parameterised stratospheric mountain-wave-induced temperature fluctuations over the Antarctic Peninsula from a 30-year run of the global chemistry-climate configuration of the UM-UKCA model against climatologies of Atmospheric Infrared Sounder (AIRS) radiance measurements and high-resolution radiosonde temperature soundings from Rothera. The results demonstrate that the local mountain wave-induced cooling phases computed by the scheme are in relatively good agreement with both sets of observations. For example, the scheme is able to capture the observed probability distribution of the temperature fluctuations, particularly the cold tails of the distribution that are critical for exceeding the temperature threshold for PSC formation. Further analysis shows that the increased stratospheric cooling induced by the scheme results in a large increase in total PSC ‘pseudo-volume’ of the area over the Antarctic Peninsula where the model temperature exceeds the temperature threshold of formation of PSCs.

How to cite: Orr, A., Hosking, S., Delon, A., Moffat-Griffin, T., Hoffman, L., Spang, R., Abrahams, L., Keeble, J., and Braesicke, P.: Study of mountain-wave-induced stratospheric cooling over the Antarctic Peninsula using a parameterisation scheme in the UM-UKCA chemistry climate model , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19322, https://doi.org/10.5194/egusphere-egu2020-19322, 2020.