scholarly journals Boundary layer and free-tropospheric dimethyl sulfide in the Arctic spring and summer

2017 ◽  
Vol 17 (14) ◽  
pp. 8757-8770 ◽  
Author(s):  
Roghayeh Ghahremaninezhad ◽  
Ann-Lise Norman ◽  
Betty Croft ◽  
Randall V. Martin ◽  
Jeffrey R. Pierce ◽  
...  
Keyword(s):  
Dimethyl Sulfide ◽  
Transport Model ◽  
Dispersion Model ◽  
Open Water ◽  
Particle Dispersion ◽  
The Arctic ◽  
Chemical Transport Model ◽  
Model Simulations ◽  
Baffin Bay ◽  
Mixing Ratios

Abstract. Vertical distributions of atmospheric dimethyl sulfide (DMS(g)) were sampled aboard the research aircraft Polar 6 near Lancaster Sound, Nunavut, Canada, in July 2014 and on pan-Arctic flights in April 2015 that started from Longyearbyen, Spitzbergen, and passed through Alert and Eureka, Nunavut, and Inuvik, Northwest Territories. Larger mean DMS(g) mixing ratios were present during April 2015 (campaign mean of 116  ±  8 pptv) compared to July 2014 (campaign mean of 20  ±  6 pptv). During July 2014, the largest mixing ratios were found near the surface over the ice edge and open water. DMS(g) mixing ratios decreased with altitude up to about 3 km. During April 2015, profiles of DMS(g) were more uniform with height and some profiles showed an increase with altitude. DMS reached as high as 100 pptv near 2500 m. Relative to the observation averages, GEOS-Chem (www.geos-chem.org) chemical transport model simulations were higher during July and lower during April. Based on the simulations, more than 90 % of the July DMS(g) below 2 km and more than 90 % of the April DMS(g) originated from Arctic seawater (north of 66° N). During April, 60 % of the DMS(g), between 500 and 3000 m originated from Arctic seawater. During July 2014, FLEXPART (FLEXible PARTicle dispersion model) simulations locate the sampled air mass over Baffin Bay and the Canadian Arctic Archipelago 4 days back from the observations. During April 2015, the locations of the air masses 4 days back from sampling were varied: Baffin Bay/Canadian Archipelago, the Arctic Ocean, Greenland and the Pacific Ocean. Our results highlight the role of open water below the flight as the source of DMS(g) during July 2014 and the influence of long-range transport (LRT) of DMS(g) from further afield in the Arctic above 2500 m during April 2015.

scholarly journals Vertical profile of atmospheric dimethyl sulfide in the Arctic Spring and Summer

2017 ◽  
Author(s):  
Roghayeh Ghahremaninezhad ◽  
Ann-Lise Norman ◽  
Betty Croft ◽  
Randall V. Martin ◽  
Jeffrey R. Pierce ◽  
...  
Keyword(s):  
Dimethyl Sulfide ◽  
Transport Model ◽  
Open Water ◽  
The Arctic ◽  
Chemical Transport Model ◽  
Air Mass ◽  
Baffin Bay ◽  
Mixing Ratios ◽  
Vertical Distributions ◽  
Research Aircraft

Abstract. Vertical distributions of atmospheric dimethyl sulfide (DMS(g)) were sampled aboard the research aircraft Polar 6 near Lancaster Sound, Nunavut, Canada in July 2014 and on pan-Arctic flights in April 2015 that started from Longyearbyen, Spitzbergen, and passed through Alert and Eureka, Nunavut and Inuvik, Northwest Territories. Larger mean DMS(g) mixing ratios were present during April 2015 (campaign-mean of 116±8 pptv) compared to July 2014 (campaign-mean of 20±6 pptv). Observations in July 2014 indicated a decrease in DMS(g) mixing ratios with altitude up to about 3 km, and the largest mixing ratios were found near the surface above ice-edge and open water, coincident with increased particle concentrations. In contrast, DMS(g) mixing ratios sampled in April 2015 were as high as 100 pptv near 2500 m. The April campaign also exhibited uniform campaign-mean vertical profiles overall although some profiles showed an increase with altitude. GEOS-Chem chemical-transport model simulations indicate that Arctic seawater (north of 66° N) contributes the majority of DMS(g) to the Arctic profiles (>90 %) in July 2014 flight tracks which were below 3000 m. More than 90 % of DMS(g) in April 2015 was from Arctic seawater for measurements below 500 m, but that declined to 60 % for altitudes between 500 m and 3000 m. FLEXPART simulations indicate that for summer 2014, the sampled air mass originated over Baffin Bay and the Canadian Arctic Archipelago. Whereas, for springtime 2015, the air mass sampled on flights near Alert and Eureka originated from Baffin Bay/Canadian Archipelago and from long-range transport (LRT) around the northern tip of Greenland. Our results highlight the role of open water below the flight as the source of DMS(g) during July 2014, and the influence of LRT of DMS(g) from further afield in the Arctic above 2500 m during April 2015.

scholarly journals Surface ozone and its precursors at Summit, Greenland: comparison between observations and model simulations

2017 ◽  
Vol 17 (23) ◽  
pp. 14661-14674 ◽  
Author(s):  
Yaoxian Huang ◽  
Shiliang Wu ◽  
Louisa J. Kramer ◽  
Detlev Helmig ◽  
Richard E. Honrath
Keyword(s):  
Transport Model ◽  
Surface Ozone ◽  
The Arctic ◽  
Chemical Transport Model ◽  
Atmospheric Models ◽  
Contributing Factors ◽  
Model Simulations ◽  
Mixing Ratios ◽  
The Us ◽  
Coarse Model

Abstract. Recent studies have shown significant challenges for atmospheric models to simulate tropospheric ozone (O3) and its precursors in the Arctic. In this study, ground-based data were combined with a global 3-D chemical transport model (GEOS-Chem) to examine the abundance and seasonal variations of O3 and its precursors at Summit, Greenland (72.34° N, 38.29° W; 3212 m a.s.l.). Model simulations for atmospheric nitrogen oxides (NOx), peroxyacetyl nitrate (PAN), ethane (C2H6), propane (C3H8), carbon monoxide (CO), and O3 for the period July 2008–June 2010 were compared with observations. The model performed well in simulating certain species (such as CO and C3H8), but some significant discrepancies were identified for other species and further investigated. The model generally underestimated NOx and PAN (by  ∼  50 and 30 %, respectively) for March–June. Likely contributing factors to the low bias include missing NOx and PAN emissions from snowpack chemistry in the model. At the same time, the model overestimated NOx mixing ratios by more than a factor of 2 in wintertime, with episodic NOx mixing ratios up to 15 times higher than the typical NOx levels at Summit. Further investigation showed that these simulated episodic NOx spikes were always associated with transport events from Europe, but the exact cause remained unclear. The model systematically overestimated C2H6 mixing ratios by approximately 20 % relative to observations. This discrepancy can be resolved by decreasing anthropogenic C2H6 emissions over Asia and the US by  ∼ 20 %, from 5.4 to 4.4 Tg year−1. GEOS-Chem was able to reproduce the seasonal variability of O3 and its spring maximum. However, compared with observations, it underestimated surface O3 by approximately 13 % (6.5 ppbv) from April to July. This low bias appeared to be driven by several factors including missing snowpack emissions of NOx and nitrous acid in the model, the weak simulated stratosphere-to-troposphere exchange flux of O3 over the summit, and the coarse model resolution.

scholarly journals Dimethyl sulfide in the summertime Arctic atmosphere: measurements and source sensitivity simulations

2016 ◽  
Vol 16 (11) ◽  
pp. 6665-6680 ◽  
Author(s):  
Emma L. Mungall ◽  
Betty Croft ◽  
Martine Lizotte ◽  
Jennie L. Thomas ◽  
Jennifer G. Murphy ◽  
...  
Keyword(s):  
Dimethyl Sulfide ◽  
Transport Model ◽  
Sulfur Cycle ◽  
Oxidation Products ◽  
The Arctic ◽  
High Time Resolution ◽  
Study Region ◽  
Baffin Bay ◽  
Mixing Ratios ◽  
Arctic Atmosphere

Abstract. Dimethyl sulfide (DMS) plays a major role in the global sulfur cycle. In addition, its atmospheric oxidation products contribute to the formation and growth of atmospheric aerosol particles, thereby influencing cloud condensation nuclei (CCN) populations and thus cloud formation. The pristine summertime Arctic atmosphere is strongly influenced by DMS. However, atmospheric DMS mixing ratios have only rarely been measured in the summertime Arctic. During July–August, 2014, we conducted the first high time resolution (10 Hz) DMS mixing ratio measurements for the eastern Canadian Archipelago and Baffin Bay as one component of the Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments (NETCARE). DMS mixing ratios ranged from below the detection limit of 4 to 1155 pptv (median 186 pptv) during the 21-day shipboard campaign. A transfer velocity parameterization from the literature coupled with coincident atmospheric and seawater DMS measurements yielded air–sea DMS flux estimates ranging from 0.02 to 12 µmol m−2 d−1. Air-mass trajectory analysis using FLEXPART-WRF and sensitivity simulations with the GEOS-Chem chemical transport model indicated that local sources (Lancaster Sound and Baffin Bay) were the dominant contributors to the DMS measured along the 21-day ship track, with episodic transport from the Hudson Bay System. After adjusting GEOS-Chem oceanic DMS values in the region to match measurements, GEOS-Chem reproduced the major features of the measured time series but was biased low overall (2–1006 pptv, median 72 pptv), although within the range of uncertainty of the seawater DMS source. However, during some 1–2 day periods the model underpredicted the measurements by more than an order of magnitude. Sensitivity tests indicated that non-marine sources (lakes, biomass burning, melt ponds, and coastal tundra) could make additional episodic contributions to atmospheric DMS in the study region, although local marine sources of DMS dominated. Our results highlight the need for both atmospheric and seawater DMS data sets with greater spatial and temporal resolution, combined with further investigation of non-marine DMS sources for the Arctic.

scholarly journals Tropospheric ozone and its precursors at Summit, Greenland: comparison between observations and model simulations

2017 ◽  
Author(s):  
Yaoxian Huang ◽  
Shiliang Wu ◽  
Louisa J. Kramer ◽  
Detlev Helmig ◽  
Richard E. Honrath
Keyword(s):  
Tropospheric Ozone ◽  
Transport Model ◽  
Deposition Velocity ◽  
The Arctic ◽  
Chemical Transport Model ◽  
Contributing Factors ◽  
Model Simulations ◽  
Mixing Ratios ◽  
Resolution Model ◽  
Coarse Model

Abstract. Recent studies have shown some significant challenges for atmospheric models to simulate tropospheric ozone (O3) and some of its precursors in the Arctic. In this study, ground based data are combined with a global 3-D chemical transport model (GEOS-Chem) to examine the abundance and seasonal variations of O3 and its precursors at Summit, Greenland (72.34˚ N, 38.29˚ W, 3212 m a.s.l). Model simulations for atmospheric nitrogen oxides (NOx), peroxyacetyl nitrate (PAN), ethane (C2H6), propane (C3H8), carbon monoxide (CO), and O3 for the period of 07/2008–06/2010 are compared with observations. The model performs well in simulating certain species (such as CO and C3H8), but some significant discrepancies are identified for other species and further investigated. The model generally underestimates NOx and PAN (by around 50 % and 30 %, respectively) for March–June. Likely contributing factors to the low bias include missing NOx and PAN emissions from snowpack chemistry in the model. At the same time, the model overestimates NOx mixing ratios by more than a factor of 2 in wintertime, with episodic NOx mixing ratios up to 15 times higher than the typical NOx levels at Summit. Further investigation shows that these simulated episodic NOx spikes are always associated with transport events from Europe, but the exact cause remains unclear. The model systematically overestimates C2H6 mixing ratios by approximately 20 % relative to observations. This discrepancy can be resolved by decreasing anthropogenic C2H6 emissions over Asia and the US by 20 %, from 5.4 to 4.4 Tg/yr. GEOS-Chem is able to reproduce the seasonal variability of O3 and its spring maximum. However, compared with observations, it underestimates surface O3 by approximately 13 % (6.5 ppbv) from April to July. This low bias appears to be driven by several factors including missing snowpack emissions for NOx and nitrous acid, the coarse model resolution, model overestimated O3 dry deposition velocity during springtime, as well as the uncertainties in the stratosphere-to-troposphere exchange scheme for O3.

scholarly journals Record-breaking ozone loss in the Arctic winter 2010/2011: comparison with 1996/1997

2012 ◽  
Vol 12 (15) ◽  
pp. 7073-7085 ◽  
Author(s):  
J. Kuttippurath ◽  
S. Godin-Beekmann ◽  
F. Lefèvre ◽  
G. Nikulin ◽  
M. L. Santee ◽  
...  
Keyword(s):  
Transport Model ◽  
Chemical Transport ◽  
The Arctic ◽  
Altitude Range ◽  
Chemical Transport Model ◽  
Model Simulations ◽  
Ozone Loss ◽  
Elevated Ozone ◽  
Record Value ◽  
First Time

Abstract. We present a detailed discussion of the chemical and dynamical processes in the Arctic winters 1996/1997 and 2010/2011 with high resolution chemical transport model (CTM) simulations and space-based observations. In the Arctic winter 2010/2011, the lower stratospheric minimum temperatures were below 195 K for a record period of time, from December to mid-April, and a strong and stable vortex was present during that period. Simulations with the Mimosa-Chim CTM show that the chemical ozone loss started in early January and progressed slowly to 1 ppmv (parts per million by volume) by late February. The loss intensified by early March and reached a record maximum of ~2.4 ppmv in the late March–early April period over a broad altitude range of 450–550 K. This coincides with elevated ozone loss rates of 2–4 ppbv sh−1 (parts per billion by volume/sunlit hour) and a contribution of about 30–55% and 30–35% from the ClO-ClO and ClO-BrO cycles, respectively, in late February and March. In addition, a contribution of 30–50% from the HOx cycle is also estimated in April. We also estimate a loss of about 0.7–1.2 ppmv contributed (75%) by the NOx cycle at 550–700 K. The ozone loss estimated in the partial column range of 350–550 K exhibits a record value of ~148 DU (Dobson Unit). This is the largest ozone loss ever estimated in the Arctic and is consistent with the remarkable chlorine activation and strong denitrification (40–50%) during the winter, as the modeled ClO shows ~1.8 ppbv in early January and ~1 ppbv in March at 450–550 K. These model results are in excellent agreement with those found from the Aura Microwave Limb Sounder observations. Our analyses also show that the ozone loss in 2010/2011 is close to that found in some Antarctic winters, for the first time in the observed history. Though the winter 1996/1997 was also very cold in March–April, the temperatures were higher in December–February, and, therefore, chlorine activation was moderate and ozone loss was average with about 1.2 ppmv at 475–550 K or 42 DU at 350–550 K, as diagnosed from the model simulations and measurements.

scholarly journals Inversion of long-lived trace gas emissions using combined Eulerian and Lagrangian chemical transport models

2011 ◽  
Vol 11 (18) ◽  
pp. 9887-9898 ◽  
Author(s):  
M. Rigby ◽  
A. J. Manning ◽  
R. G. Prinn
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Transport Model ◽  
Initial Conditions ◽  
Dispersion Model ◽  
Chemical Transport ◽  
Particle Dispersion ◽  
Global Network ◽  
Lagrangian Model ◽  
Chemical Transport Model

Abstract. We present a method for estimating emissions of long-lived trace gases from a sparse global network of high-frequency observatories, using both a global Eulerian chemical transport model and Lagrangian particle dispersion model. Emissions are derived in a single step after determining sensitivities of the observations to initial conditions, the high-resolution emissions field close to observation points, and larger regions further from the measurements. This method has the several advantages over inversions using one type of model alone, in that: high-resolution simulations can be carried out in limited domains close to the measurement sites, with lower resolution being used further from them; the influence of errors due to aggregation of emissions close to the measurement sites can be minimized; assumptions about boundary conditions to the Lagrangian model do not need to be made, since the entire emissions field is estimated; any combination of appropriate models can be used, with no code modification. Because the sensitivity to the entire emissions field is derived, the estimation can be carried out using traditional statistical methods without the need for multiple steps in the inversion. We demonstrate the utility of this approach by determining global SF6 emissions using measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) between 2007 and 2009. The global total and large-scale patterns of the derived emissions agree well with previous studies, whilst allowing emissions to be determined at higher resolution than has previously been possible, and improving the agreement between the modeled and observed mole fractions at some sites.

scholarly journals Around the world in 17 days - hemispheric-scale transport of forest fire smoke from Russia in May 2003

2004 ◽  
Vol 4 (5) ◽  
pp. 1311-1321 ◽  
Author(s):  
R. Damoah ◽  
N. Spichtinger ◽  
C. Forster ◽  
P. James ◽  
I. Mattis ◽  
...  
Keyword(s):  
Forest Fires ◽  
Transport Model ◽  
Dispersion Model ◽  
Weather Forecast ◽  
Analysis Data ◽  
Particle Dispersion ◽  
Transport Processes ◽  
Wide Field ◽  
Medium Range Weather Forecast ◽  
Model Simulations

Abstract. In May 2003, severe forest fires in southeast Russia resulted in smoke plumes extending widely across the Northern Hemisphere. This study combines satellite data from a variety of platforms (Moderate Resolution Imaging Spectroradiometer (MODIS), Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Earth Probe Total Ozone Mapping Spectrometer (TOMS) and Global Ozone Monitoring Experiment (GOME)) and vertical aerosol profiles derived with Raman lidar measurements with results from a Lagrangian particle dispersion model to understand the transport processes that led to the large haze plumes observed over North America and Europe. The satellite images provided a unique opportunity for validating model simulations of tropospheric transport on a truly hemispheric scale. Transport of the smoke occurred in two directions: Smoke travelling northwestwards towards Scandinavia was lifted over the Urals and arrived over the Norwegian Sea. Smoke travelling eastwards to the Okhotsk Sea was also lifted, it then crossed the Bering Sea to Alaska from where it proceeded to Canada and was later even observed over Scandinavia and Eastern Europe on its way back to Russia. Not many events of this kind, if any, have been observed, documented and simulated with a transport model comprehensively. The total transport time was about 17 days. We compared transport model simulations using meteorological analysis data from both the European Centre for Medium-Range Weather Forecast (ECMWF) and the National Center for Environmental Prediction (NCEP) in order to find out how well this event could be simulated using these two datasets. Although differences between the two simulations are found on small scales, both agree remarkably well with each other and with the observations on large scales. On the basis of the available observations, it cannot be decided which simulation was more realistic.

scholarly journals High-ozone layers in the middle and upper troposphere above Central Europe: potential import from the stratosphere along the subtropical jet stream

2011 ◽  
Vol 11 (17) ◽  
pp. 9343-9366 ◽  
Author(s):  
T. Trickl ◽  
N. Bärtsch-Ritter ◽  
H. Eisele ◽  
M. Furger ◽  
R. Mücke ◽  
...  
Keyword(s):  
Transport Model ◽  
Dispersion Model ◽  
Warm Season ◽  
Particle Dispersion ◽  
Jet Stream ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Subtropical Jet Stream ◽  
Subtropical Jet ◽  
The Pacific

Abstract. Specific very dry high-ozone layers, starting roughly two days after the onset of high-pressure periods during the warm season, have been reproducibly observed in the middle and upper troposphere with the ozone lidar in Garmisch-Partenkirchen (Germany). These episodes, previously not understood, were recently analysed based on extending backward simulations with the FLEXPART particle dispersion model to as many as twenty days and on jet-stream analyses including calculations with the LAGRANTO transport model. In all six cases analysed the model results indicate ozone import from the stratosphere on an extremely long path along the subtropical jet stream over the Pacific Ocean, Asia and, in part, all the way back to the Atlantic Ocean. The analysis suggests that stratospheric influence is the most important factor for the increase in ozone and is related to rather shallow transfer of air from the stratosphere into the upper- and mid-tropospheric air streams observed with the lidar. Contributions from the boundary layers of East Asia and North America are just occasionally present, in one case documented by a very dense aerosol plume from the Asian deserts. The considerable vertical and temporal extent of many of these layers and peak ozone mixing ratios between 80 and 150 ppb suggest that the observations are related to an important mechanism for stratosphere-to-troposphere transport (STT) and also confirm the model predictions of pronounced and persistent STT along the subtropical jet stream.

scholarly journals Episodes of cross-polar transport in the Arctic troposphere during July 2008 as seen from models, satellite, and aircraft observations

2010 ◽  
Vol 10 (11) ◽  
pp. 26361-26410 ◽  
Author(s):  
H. Sodemann ◽  
M. Pommier ◽  
S. R. Arnold ◽  
S. A. Monks ◽  
K. Stebel ◽  
...  
Keyword(s):  
Transport Model ◽  
Chemical Transport ◽  
The Arctic ◽  
Actual State ◽  
Chemical Transport Model ◽  
Horizontal Structure ◽  
Model Simulations ◽  
Aircraft Observations ◽  
Total Column ◽  
Aircraft Data

Abstract. During the POLARCAT summer campaign in 2008, two episodes (2–5 July and 7–10 July 2008) occurred where low-pressure systems traveled from Siberia across the Arctic Ocean towards the North Pole. The two cyclones had extensive smoke plumes embedded in their associated air masses, creating an excellent opportunity to use satellite and aircraft observations to validate the performance of atmospheric transport models in the Arctic, which is a challenging model domain due to numerical and other complications. Here we compare transport simulations of carbon monoxide (CO) from the Lagrangian transport model FLEXPART, the Eulerian chemical transport model TOMCAT, and for numerical aspects the limited-area chemical transport model WRF-Chem. Retrievals of total column CO from the IASI passive infrared sensor onboard the MetOp-A satellite are used as a total column CO reference for the two simulations. Main aspect of the comparison is how realistic horizontal and vertical structures are represented in the model simulations. Analysis of CALIPSO lidar curtains and in situ aircraft measurements provide further independent reference points to assess how reliable the model simulations are and what the main limitations are. The horizontal structure of mid-latitude pollution plumes agrees well between the IASI total column CO and the model simulations. However, finer-scale structures are too quickly diffused in the Eulerian models. Aircraft data suggest that the satellite data are biased high, while TOMCAT and WRF-Chem are biased low. FLEXPART fits the aircraft data rather well, but due to added background concentrations the simulation is not independent from observations. The multi-data, multi-model approach allows separating the influences of meteorological fields, model realisation, and grid type on the plume structure. In addition to the very good agreement between simulated and observed total column CO fields, the results also highlight the difficulty to identify a data set that most realistically represents the actual state of the atmosphere.

scholarly journals Record-breaking ozone loss in the Arctic winter 2010/2011: comparison with 1996/1997

2012 ◽  
Vol 12 (3) ◽  
pp. 6877-6908
Author(s):  
J. Kuttippurath ◽  
S. Godin-Beekmann ◽  
F. Lefèvre ◽  
G. Nikulin ◽  
M. L. Santee ◽  
...  
Keyword(s):  
Transport Model ◽  
Chemical Transport ◽  
The Arctic ◽  
Altitude Range ◽  
Chemical Transport Model ◽  
Model Simulations ◽  
Ozone Loss ◽  
Elevated Ozone ◽  
Record Value ◽  
First Time

Abstract. We present a detailed discussion of the chemical and dynamical processes in the Arctic winters 1996/1997 and 2010/2011 with high resolution chemical transport model (CTM) simulations and space-based observations. In the Arctic winter 2010/2011, the lower stratospheric minimum temperatures were below 195 K for a record period, from December to mid-April, and a strong and stable vortex was present during that period. Analyses with the Mimosa-Chim CTM simulations show that the chemical ozone loss started by early January and progressed slowly to 1 ppmv (parts per million by volume) by late February. The loss intensified by early March and reached a record maximum of ~2.4 ppmv in the late March–early April period over a broad altitude range of 450–550 K. This coincides with elevated ozone loss rates of 2–4 ppbv sh−1 (parts per billion by volume/sunlit hour) and a contribution of about 40% from the ClO–ClO cycle and about 35–40% from the ClO-BrO cycle in late February and March, and about 30–50% from the HOx cycle in April. We also estimate a loss of around 0.7–1.2 ppmv contributed (75%) by the NOx cycle at 550–700 K. The ozone loss estimated in the partial column range of 350–550 K also exhibits a record value of ~148 DU (Dobson Unit). This is the largest ozone loss ever estimated in the Arctic and is consistent with the remarkable chlorine activation and strong denitrification (40–50%) during the winter, as the modeled ClO shows ~1.8 ppbv in early January and ~1 ppbv in March at 450–550 K. These model results are in excellent agreement with those found from the Aura Microwave Limb Sounder observations. Our analyses also show that the ozone loss in 2010/2011 is close to that found in some Antarctic winters, for the first time in the observed history. Though the winter 1996/1997 was also very cold in March–April, the temperatures were higher in December–February, and, therefore, chlorine activation was moderate and ozone loss was average with about 1.2 ppmv at 475–550 K or 42 DU at 350–550 K, as diagnosed from the model simulations and measurements.

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