scholarly journals Vertical and interhemispheric links in the stratosphere-mesosphere as revealed by the day-to-day variability of Aura-MLS temperature data

2009 ◽  
Vol 27 (9) ◽  
pp. 3387-3409 ◽  
Author(s):  
X. Xu ◽  
A. H. Manson ◽  
C. E. Meek ◽  
T. Chshyolkova ◽  
J. R. Drummond ◽  
...  
Keyword(s):  
Middle Atmosphere ◽  
Chemical Constituents ◽  
Polar Vortex ◽  
Temperature Data ◽  
The Arctic ◽  
Time Lags ◽  
Research Activity ◽  
Mean Temperature ◽  
The Antarctic ◽  
Coupling Processes

Abstract. The coupling processes in the middle atmosphere have been a subject of intense research activity because of their effects on atmospheric circulation, structure, variability, and the distribution of chemical constituents. In this study, the day-to-day variability of Aura-MLS (Microwave Limb Sounder) temperature data are used to reveal the vertical and interhemispheric coupling processes in the stratosphere-mesosphere during four Northern Hemisphere winters (2004/2005–2007/2008). The UKMO (United Kingdom Meteorological Office) assimilated data and mesospheric winds from MF (medium frequency) radars are also applied to help highlight the coupling processes. In this study, a clear vertical link can be seen between the stratosphere and mesosphere during winter months. The coolings and reversals of northward meridional winds in the polar winter mesosphere are often observed in relation to warming events (Sudden Stratospheric Warming, SSW for short) and the associated changes in zonal winds in the polar winter stratosphere. An upper-mesospheric cooling usually precedes the beginning of the warming in the stratosphere by 1–2 days. Inter-hemispheric coupling has been identified initially by a correlation analysis using the year-to-year monthly zonal mean temperature. Then the correlation analyses are performed based upon the daily zonal mean temperature. From the original time sequences, significant positive (negative) correlations are generally found between zonal mean temperatures at the Antarctic summer mesopause and in the Arctic winter stratosphere (mesosphere) during northern mid-winters, although these correlations are dominated by the low frequency variability (i.e. the seasonal trend). Using the short-term oscillations (less than 15 days), the statistical result, by looking for the largest magnitude of correlation within a range of time-lags (0 to 10 days; positive lags mean that the Antarctic summer mesopause is lagging), indicates that the temporal variability of zonal mean temperature at the Antarctic summer mesopause is also positively (negatively) correlated with the polar winter stratosphere (mesosphere) during three (2004/2005, 2005/2006, and 2007/2008) out of the four winters. The highest value of the correlation coefficient is over 0.7 in the winter-stratosphere for the three winters. The remaining winter (2006/2007) has more complex correlations structures; correspondingly the polar vortex was distinguished this winter. The time-lags obtained for 2004/2005 and 2006/2007 are distinct from 2005/2006 and 2007/2008 where a 6-day lag dominates for the coupling between the winter stratosphere and the summer mesopause. The correlations are also provided using temperatures in northern longitudinal sectors in a comparison with the Antarctic-mesopause zonal mean temperature. For northern mid-high latitudes (~50–70° N), temperatures in Scandinavia-Eastern Europe and in the Pacific-Western Canada longitudinal sectors often have opposite signs of correlations with zonal mean temperatures near the Antarctic summer mesopause during northern mid-winters. The statistical results are shown to be associated with the Northern Hemisphere's polar vortex characteristics.

scholarly journals Stratospheric temperatures and tracer transport in a nudged 4-year middle atmosphere GCM simulation

2005 ◽  
Vol 5 (1) ◽  
pp. 961-1006 ◽  
Author(s):  
M. K. van Aalst ◽  
J. Lelieveld ◽  
B. Steil ◽  
C. Brühl ◽  
P. Jöckel ◽  
...  
Keyword(s):  
Interannual Variability ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Detailed Comparison ◽  
The Arctic ◽  
Cold Bias ◽  
Tracer Transport ◽  
Quasi Biennial Oscillation ◽  
The Antarctic

Abstract. We have performed a 4-year simulation with the Middle Atmosphere General Circulation Model MAECHAM5/MESSy, while slightly nudging the model’s meteorology in the free troposphere (below 113 hPa) towards ECMWF analyses. We show that the nudging 5 technique, which leaves the middle atmosphere almost entirely free, enables comparisons with synoptic observations. The model successfully reproduces many specific features of the interannual variability, including details of the Antarctic vortex structure. In the Arctic, the model captures general features of the interannual variability, but falls short in reproducing the timing of sudden stratospheric warmings. A 10 detailed comparison of the nudged model simulations with ECMWF data shows that the model simulates realistic stratospheric temperature distributions and variabilities, including the temperature minima in the Antarctic vortex. Some small (a few K) model biases were also identified, including a summer cold bias at both poles, and a general cold bias in the lower stratosphere, most pronounced in midlatitudes. A comparison 15 of tracer distributions with HALOE observations shows that the model successfully reproduces specific aspects of the instantaneous circulation. The main tracer transport deficiencies occur in the polar lowermost stratosphere. These are related to the tropopause altitude as well as the tracer advection scheme and model resolution. The additional nudging of equatorial zonal winds, forcing the quasi-biennial oscillation, sig20 nificantly improves stratospheric temperatures and tracer distributions.

scholarly journals Statistical Characterization of Arctic Polar-Night Jet Oscillation Events

2013 ◽  
Vol 26 (6) ◽  
pp. 2096-2116 ◽  
Author(s):  
Peter Hitchcock ◽  
Theodore G. Shepherd ◽  
Gloria L. Manney
Keyword(s):  
Time Scale ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Extended Period ◽  
The Arctic ◽  
Polar Night ◽  
Stratospheric Polar Vortex ◽  
Statistical Characterization ◽  
Long Time ◽  
Jet Oscillation

Abstract A novel diagnostic tool is presented, based on polar-cap temperature anomalies, for visualizing daily variability of the Arctic stratospheric polar vortex over multiple decades. This visualization illustrates the ubiquity of extended-time-scale recoveries from stratospheric sudden warmings, termed here polar-night jet oscillation (PJO) events. These are characterized by an anomalously warm polar lower stratosphere that persists for several months. Following the initial warming, a cold anomaly forms in the middle stratosphere, as does an anomalously high stratopause, both of which descend while the lower-stratospheric anomaly persists. These events are characterized in four datasets: Microwave Limb Sounder (MLS) temperature observations; the 40-yr ECMWF Re-Analysis (ERA-40) and Modern Era Retrospective Analysis for Research and Applications (MERRA) reanalyses; and an ensemble of three 150-yr simulations from the Canadian Middle Atmosphere Model. The statistics of PJO events in the model are found to agree very closely with those of the observations and reanalyses. The time scale for the recovery of the polar vortex following sudden warmings correlates strongly with the depth to which the warming initially descends. PJO events occur following roughly half of all major sudden warmings and are associated with an extended period of suppressed wave-activity fluxes entering the polar vortex. They follow vortex splits more frequently than they do vortex displacements. They are also related to weak vortex events as identified by the northern annular mode; in particular, those weak vortex events followed by a PJO event show a stronger tropospheric response. The long time scales, predominantly radiative dynamics, and tropospheric influence of PJO events suggest that they represent an important source of conditional skill in seasonal forecasting.

scholarly journals Investigation of Arctic middle-atmospheric dynamics using 3 years of H<sub>2</sub>O and O<sub>3</sub> measurements from microwave radiometers at Ny-Ålesund

2019 ◽  
Author(s):  
Franziska Schranz ◽  
Brigitte Tschanz ◽  
Rolf Rüfenacht ◽  
Klemens Hocke ◽  
Mathias Palm ◽  
...  
Keyword(s):  
Water Vapour ◽  
Middle Atmosphere ◽  
Microwave Radiometer ◽  
Polar Vortex ◽  
The Arctic ◽  
High Time Resolution ◽  
Middle Atmospheric Dynamics ◽  
Wind Profiles ◽  
Microwave Radiometers

Abstract. We use 3 years of water vapour and ozone measurements to analyse dynamical events in the polar middle atmosphere such as sudden stratospheric warmings (SSW), polar vortex shifts, water vapour descent rates and periodicities. The measurements were performed with the two ground-based microwave radiometers MIAWARA-C and GROMOS-C which are co-located at the AWIPEV research base at Ny-Ålesund, Svalbard (79° N, 12° E) since September 2015. The almost continuous datasets of water vapour and ozone are characterised by a high time resolution in the order of hours. A thorough intercomparison of these datasets with models and measurements from satellite, ground-based and in-situ instruments was performed. In the upper stratosphere and lower mesosphere the MIAWARA-C profiles agree within 5 % with SD-WACCM simulations and ACE-FTS measurements whereas AuraMLS measurements show an average offset of 10–15 % depending on altitude but constant in time. Stratospheric GROMOS-C profiles are within 5 % of the satellite instruments AuraMLS and ACE-FTS and the ground-based microwave radiometer OZORAM which is also located at Ny-Ålesund. During these first three years of the measurement campaign typical phenomena of the Arctic middle atmosphere took place and we analysed their signatures in the water vapour and ozone datasets. Inside of the polar vortex in autumn we found the descent rate of mesospheric water vapour to be 435 m/day on average. In early 2017 distinct increases in mesospheric water vapour of about 2 ppm were observed when the polar vortex was displaced and midlatitude air was brought to Ny-Ålesund. Two major sudden stratospheric warmings took place in March 2016 and February 2018 where ozone enhancements of up to 4 ppm were observed. The zonal wind reversals accompanying a major SSW were captured in the GROMOS-C wind profiles which are retrieved from the ozone spectra. After the SSW in February 2018 the polar vortex re-established and the water vapour descent rate in the mesosphere was 355 m/day. In the water vapour and ozone time series signatures of atmospheric waves with periods close to 2, 5, 10 and 16 days were found.

scholarly journals Middle atmospheric water vapour and dynamics in the vicinity of the polar vortex during the Hygrosonde-2 campaign

2009 ◽  
Vol 9 (13) ◽  
pp. 4407-4417 ◽  
Author(s):  
S. Lossow ◽  
M. Khaplanov ◽  
J. Gumbel ◽  
J. Stegman ◽  
G. Witt ◽  
...  
Keyword(s):  
Water Vapour ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
The Arctic ◽  
Small Scale ◽  
Air Masses ◽  
Mixing Ratios ◽  
Water Vapour Concentration ◽  
Wind Shears

Abstract. The Hygrosonde-2 campaign took place on 16 December 2001 at Esrange/Sweden (68° N, 21° E) with the aim to investigate the small scale distribution of water vapour in the middle atmosphere in the vicinity of the Arctic polar vortex. In situ balloon and rocket-borne measurements of water vapour were performed by means of OH fluorescence hygrometry. The combined measurements yielded a high resolution water vapour profile up to an altitude of 75 km. Using the characteristic of water vapour being a dynamical tracer it was possible to directly relate the water vapour data to the location of the polar vortex edge, which separates air masses of different character inside and outside the polar vortex. The measurements probed extra-vortex air in the altitude range between 45 km and 60 km and vortex air elsewhere. Transitions between vortex and extra-vortex usually coincided with wind shears caused by gravity waves which advect air masses with different water vapour volume mixing ratios. From the combination of the results from the Hygrosonde-2 campaign and the first flight of the optical hygrometer in 1994 (Hygrosonde-1) a clear picture of the characteristic water vapour distribution inside and outside the polar vortex can be drawn. Systematic differences in the water vapour concentration between the inside and outside of the polar vortex can be observed all the way up into the mesosphere. It is also evident that in situ measurements with high spatial resolution are needed to fully account for the small-scale exchange processes in the polar winter middle atmosphere.

scholarly journals Comparison of Inorganic Chlorine in the Southern Hemispheric lowermost stratosphere during Late Winter 2019

2021 ◽  
Author(s):  
Markus Jesswein ◽  
Heiko Bozem ◽  
Hans-Christoph Lachnitt ◽  
Peter Hoor ◽  
Thomas Wagenhäuser ◽  
...  
Keyword(s):  
Degradation Products ◽  
Polar Vortex ◽  
Boundary Region ◽  
Early Spring ◽  
Active Chlorine ◽  
The Arctic ◽  
Late Winter ◽  
Annual Variations ◽  
The Difference ◽  
The Antarctic

Abstract. Inorganic chlorine (Cly) is the sum of the degradation products of long-lived chlorinated source gases. These include the reservoir species (HCl and ClONO2) and active chlorine species (i.e. ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in late winter and early spring 2019. Results are compared to Cly of the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and mid-latitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687 ± 20 ppt at 385 K, therefore up to around 50 % of total chlorine could be found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine could be found in inorganic form in the southern mid-latitudes. In contrast, only 40 % of total chlorine could be found in inorganic form in the Arctic vortex during PGS and roughly 20 % in the northern mid-latitudes. Differences inside the respective vortex reaches up to 565 ppt more Cly in the Antarctic vortex 2019 than in the Arctic vortex 2016 (at comparable distance to the local tropopause). As far as is known, this is the first comparison of inorganic chlorine within the respective polar vortex. Based on the results of these two campaigns, the difference of Cly inside the respective vortex is significant and larger than reported inter annual variations.

scholarly journals Climatological features of stratospheric streamers in the FUB-CMAM with increased horizontal resolution

2004 ◽  
Vol 4 (5) ◽  
pp. 6789-6822
Author(s):  
K. Krüger ◽  
U. Langematz ◽  
J. L. Grenfell ◽  
K. Labitzke
Keyword(s):  
East Asia ◽  
Total Ozone ◽  
Large Scale ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Horizontal Resolution ◽  
Transport Processes ◽  
The Arctic ◽  
Future Climate Change ◽  
Good Correspondence

Abstract. The purpose of this study is to investigate horizontal transport processes in the winter stratosphere using data with a high spatial and temporal resolution. For this reason the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) with its model top at 83 km altitude, increased horizontal resolution T42 and the semi-Lagrangian transport scheme for advecting passive tracers is used. A new result of this paper is the classification of specific transport phenomena within the stratosphere into tropical-subtropical streamer (e.g. Offermann et al., 1999) and polar vortex extrusions hereafter called polar vortex streamers. To investigate the role played by these large-scale structures on the inter-annual and seasonal variability of the observed negative ozone trend in northern mid-latitudes, the global occurrence of such streamers were calculated based on a 10-year model climatology, concentrating on the existence of the Arctic polar vortex. For the identification and counting of streamers, the new method of zonal anomaly was chosen, which in comparison to other methods produced the best result in this study. The analysis of the months October–May yielded a maximum occurrence of tropical-subtropical streamers during Arctic winter and spring in the middle and upper stratosphere. Synoptic maps revealed highest intensities in the subtropics over East Asia with a secondary maximum over the Atlantic in the northern hemisphere. Furthermore, tropical-subtropical streamers exhibited about a four times higher occurrence than polar vortex streamers, indicating that the subtropical barrier is more permeable than the polar vortex barrier (edge) in the model, which is in good correspondence with observations (e.g. Plumb, 2002; Neu et al., 2003). Interesting for the total ozone loss in mid-latitudes is the consideration of the lower stratosphere, where strongest ozone depletion is observed at polar latitudes (WMO, 2003). In this particular region the FUB-CMAM simulated a climatological maximum of 10% occurrence of tropical-subtropical streamers over East-Asia/West Pacific and the Atlantic during early- and mid-winter. The results of this paper demonstrate that the regular occurrence of stratospheric streamers e.g., large-scale mixing processes of tropical-subtropical and polar vortex air masses into mid-latitudes, could play a significant role on the strength and variability of the observed total ozone decrease at mid-latitudes and should not be neglected in future climate change studies.

scholarly journals Unusually strong nitric oxide descent in the Arctic middle atmosphere in early 2013 as observed by Odin/SMR

2014 ◽  
Vol 14 (3) ◽  
pp. 3563-3581
Author(s):  
K. Pérot ◽  
J. Urban ◽  
D. P. Murtagh
Keyword(s):  
Nitric Oxide ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Polar Vortex ◽  
Meteorological Conditions ◽  
Atmospheric Composition ◽  
The Arctic ◽  
The Reformation ◽  
Polar Stratosphere ◽  
Energetic Particle Precipitation

Abstract. The middle atmosphere has been affected by an exceptionally strong midwinter stratospheric sudden warming (SSW) during the Arctic winter 2012/2013. These unusual meteorological conditions led to a breakdown of the polar vortex, followed by the reformation of a strong upper stratospheric vortex associated with particularly efficient descent of air. Measurements by the Sub-Millimetre Radiometer (SMR), on board the Odin satellite, show that very large amounts of nitric oxide (NO), produced by Energetic Particle Precipitation (EPP) in the mesosphere/lower thermosphere (MLT), could thus enter the polar stratosphere in early 2013. The mechanism referring to the downward transport of EPP generated-NOx during winter is generally called the EPP indirect effect. SMR observed up to 20 times more NO in the upper stratosphere than the average NO measured at the same latitude, pressure and time during three previous winters where no mixing between mesospheric and stratospheric air was noticeable. This event turned out to be an unprecedently strong case of this effect. Our study is based on a comparison with the Arctic winter 2008/2009, when a similar situation was observed and which was so far considered as a record-breaking winter for this kind of events. This outstanding situation is the result of the combination between a relatively high geomagnetic activity and an unusually high dynamical activity, which makes this case a prime example to study the EPP impacts on the atmospheric composition.

scholarly journals Observation of an unusual mid-stratospheric aerosol layer in the Arctic: possible sources and implications for polar vortex dynamics

2003 ◽  
Vol 21 (4) ◽  
pp. 1057-1069 ◽  
Author(s):  
M. Gerding ◽  
G. Baumgarten ◽  
U. Blum ◽  
J. P. Thayer ◽  
K.-H. Fricke ◽  
...  
Keyword(s):  
Middle Atmosphere ◽  
Water Solution ◽  
Polar Vortex ◽  
Atmospheric Temperature ◽  
Stratospheric Aerosol ◽  
Atmospheric Composition ◽  
The Arctic ◽  
Aerosol Layer ◽  
Particle Sedimentation ◽  
Composition And Structure

Abstract. By the beginning of winter 2000/2001, a mysterious stratospheric aerosol layer had been detected by four different Arctic lidar stations. The aerosol layer was observed first on 16 November 2000, at an altitude of about 38 km near Søndre Strømfjord, Greenland (67° N, 51° W) and on 19 November 2000, near Andenes, Norway (69°  N, 16°  E). Subsequently, in early December 2000, the aerosol layer was observed near Kiruna, Sweden (68°  N, 21°  E) and Ny-Ålesund, Spitsbergen (79°  N, 12°  E). No mid-latitude lidar station observed the presence of aerosols in this altitude region. The layer persisted throughout the winter 2000/2001, at least up to 12 February 2001. In November 2000, the backscatter ratio at a wavelength of 532 nm was up to 1.1, with a FWHM of about 2.5 km. By early February 2001, the layer had sedimented from an altitude of 38 km to about 26 km. Measurements at several wavelengths by the ALOMAR and Koldewey lidars indicate the particle size was between 30 and 50 nm. Depolarisation measurements reveal that the particles in the layer are aspherical, hence solid. In the mid-stratosphere, the ambient atmospheric temperature was too high to support in situ formation or existence of cloud particles consisting of ice or an acid-water solution. Furthermore, in the year 2000 there was no volcanic eruption, which could have injected aerosols into the upper stratosphere. Therefore, other origins of the aerosol, such as meteoroid debris, condensed rocket fuel, or aerosols produced under the influence of charged solar particles, will be discussed in the paper. Trajectory calculations illustrate the path of the aerosol cloud within the polar vortex and are used to link the observations at the different lidar sites. From the descent rate of  the layer and particle sedimentation rates, the mean down-ward motion of air within the polar vortex was estimated to be about 124 m/d between 35 and 30 km, with higher values at the edge of the vortex.Key words. Atmospheric composition and structure (aerosols and particles; middle atmosphere composition and chemistry) – meteorology and atmospheric dynamics (middle atmosphere dynamics)

scholarly journals Record low ozone values over the Arctic in boreal spring 2020

2021 ◽  
Vol 21 (2) ◽  
pp. 617-633
Author(s):  
Martin Dameris ◽  
Diego G. Loyola ◽  
Matthias Nützel ◽  
Melanie Coldewey-Egbers ◽  
Christophe Lerot ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Total Ozone ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Ozone Hole ◽  
The Arctic ◽  
Atmospheric Conditions ◽  
Total Ozone Column ◽  
The Antarctic ◽  
Ozone Column

Abstract. Ozone data derived from the Tropospheric Monitoring Instrument (TROPOMI) sensor on board the Sentinel-5 Precursor satellite show exceptionally low total ozone columns in the polar region of the Northern Hemisphere (Arctic) in spring 2020. Minimum total ozone column values around or below 220 Dobson units (DU) were seen over the Arctic for 5 weeks in March and early April 2020. Usually the persistence of such low total ozone column values in spring is only observed in the polar Southern Hemisphere (Antarctic) and not over the Arctic. These record low total ozone columns were caused by a particularly strong polar vortex in the stratosphere with a persistent cold stratosphere at higher latitudes, a prerequisite for ozone depletion through heterogeneous chemistry. Based on the ERA5, which is the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis, the Northern Hemisphere winter 2019/2020 (from December to March) showed minimum polar cap temperatures consistently below 195 K around 20 km altitude, which enabled enhanced formation of polar stratospheric clouds. The special situation in spring 2020 is compared and discussed in context with two other Northern Hemisphere spring seasons, namely those in 1997 and 2011, which also displayed relatively low total ozone column values. However, during these years, total ozone columns below 220 DU over several consecutive days were not observed in spring. The similarities and differences of the atmospheric conditions of these three events and possible explanations for the observed features are presented and discussed. It becomes apparent that the monthly mean of the minimum total ozone column value for March 2020 (221 DU) was clearly below the respective values found in March 1997 (267 DU) and 2011 (252 DU), which highlights the special evolution of the polar stratospheric ozone layer in the Northern Hemisphere in spring 2020. A comparison with a typical ozone hole over the Antarctic (e.g., in 2016) indicates that although the Arctic spring 2020 situation is remarkable, with total ozone column values around or below 220 DU observed over a considerable area (up to 0.9 million km2), the Antarctic ozone hole shows total ozone columns typically below 150 DU over a much larger area (of the order of 20 million km2). Furthermore, total ozone columns below 220 DU are typically observed over the Antarctic for about 4 months.

scholarly journals On the observation of mesospheric air inside the arctic stratospheric polar vortex in early 2003

2005 ◽  
Vol 5 (4) ◽  
pp. 7457-7496 ◽  
Author(s):  
A. Engel ◽  
T. Möbius ◽  
H.-P. Haase ◽  
H. Bönisch ◽  
T. Wetter ◽  
...  
Keyword(s):  
Middle Atmosphere ◽  
Michelson Interferometer ◽  
Polar Vortex ◽  
The Arctic ◽  
Stratospheric Polar Vortex ◽  
Air Masses ◽  
Model Study ◽  
Tuneable Diode Laser ◽  
Ftir Spectrometer ◽  
The Difference

Abstract. During several balloon flights inside the Arctic polar vortex in early 2003, unusual trace gas distributions were observed, which indicate a strong influence of mesospheric air in the stratosphere. The tuneable diode laser (TDL) instrument SPIRALE (Spectroscopie InFrarouge par Absorption de Lasers Embarqués) measured unusually high CO values (up to 600 ppb) on 27 January at about 30 km altitude. The cryosampler BONBON sampled air masses with very high molecular Hydrogen, extremely low SF6 and enhanced CO values on 6 March at about 25 km altitude. Finally, the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) Fourier Transform Infra-Red (FTIR) spectrometer showed NOy values which are significantly higher than NOy* (the NOy derived from a correlation between N2O and NOy under undisturbed conditions), on 21 and 22 March in a layer centred at 22 km altitude. Thus, the mesospheric air seems to have been present in a layer descending from about 30 km in late January to 25 km altitude in early March and about 22 km altitude on 20 March. We present corroborating evidence from a model study using the KASIMA (KArlsruhe Simulation model of the Middle Atmosphere) model that also shows a layer of mesospheric air, which descended into the stratosphere in November and early December 2002, before the minor warming which occurred in late December 2002 lead to a descent of upper stratospheric air, cutting of a layer in which mesospheric air is present. This layer then descended inside the vortex over the course of the winter. The same feature is found in trajectory calculations, based on a large number of trajectories started in the vicinity of the observations on 6 March. Based on the difference between the mean age derived from SF6 (which has an irreversible mesospheric loss) and from CO2 (whose mesospheric loss is much smaller and reversible) we estimate that the fraction of mesospheric air in the layer observed on 6 March, must have been somewhere between 35% and 100%.

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