Major Warming Research Articles

Signatures of the Sudden Stratospheric Warming events of January–February 2008 in Seoul, S. Korea

The period January–February 2008 was characterized by four Sudden Stratospheric Warmings (SSWs) in the Northern Hemisphere, of which the last warming, at the end of February 2008, was a major warming. A significant decrease in mesospheric water vapour (H 2O) of more than 2 ppmv (∼40%) was observed by the ground-based microwave (GBMW) radiometer in Seoul, S. Korea [37.3°N, 126.3°E] during the major SSW. A comparison with ground-based mesospheric H 2O observations from the mid-latitude station in Bern [46.9°N, 7°E] revealed an anticorrelation in the mesospheric H 2O data during the major SSW. In addition, prior to the major warming, strong periodic fluctuations were recorded in the Aura MLS vertical temperature distribution between 15 and 0.05 hPa at Seoul. The mesospheric temperature oscillation was found to have a period of ∼10–14 days with a persistency of 3–4 cycles. The observed anticorrelation in mesospheric H 2O between the stations in Seoul and Bern is associated with an increased meridional flow. Trajectory calculations give evidence that H 2O-rich subtropical air had moved to Bern during the major SSW while H 2O-poor polar air was transported to Seoul. The results shown in this study are a possible indication of a strong coupling between the dynamic regimes of the low- and the high-latitude regions during SSWs.

Remote sensing of atmospheric ozone at millimeter waves

We present new results of remote sensing of the vertical distribution of ozone at millimeter waves using the FIAN (P.N. Lebedev Institute of Physics, Russian Academy of Sciences) high-sensitivity spectroradiometer which includes a new 96-channel spectrum analyzer AS-96 with improved characteristics. The ozone radiation spectrum is recorded at a frequency of 142.2 GHz. Vertical profile of ozone is retrieved using an improved algorithm based on Tikhonov’s method and statistical regularization technique. Specific features of the altitude-temporal distribution of ozone, which reflects ozonospheric processes above mid-latitudes are considered. Variations in the vertical distribution of ozone during major stratospheric warming in January 2009 are shown. It was concluded that the creation of a national ground-based network for ozone monitoring at millimeter waves in Russia is a must.

The 2009 stratospheric major warming described from synergistic use of BASCOE water vapour analyses and MLS observations

Abstract. The record-breaking major stratospheric warming of northern winter 2009 (January–February) is studied using BASCOE (Belgian Assimilation System for Chemical ObsErvation) stratospheric water vapour analyses and MLS (Microwave Limb Sounder) water vapour observations, together with meteorological data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and potential vorticity (PV) derived from ECMWF meteorological data. We focus on the interaction between the cyclonic wintertime stratospheric polar vortex and subsidiary anticyclonic stratospheric circulations during the build-up, peak and aftermath of the major warming. We show dynamical consistency between the water vapour analysed fields and the meteorological and PV fields. Using various approaches, we use the analysed water vapour fields to estimate descent in the polar vortex during this period of between ~0.5 km day−1 and ~0.7 km day−1. New results include the analysis of water vapour during the major warming and demonstration of the benefit of assimilating MLS satellite data into the BASCOE model.

On the Use of Geometric Moments to Examine the Continuum of Sudden Stratospheric Warmings

AbstractThe polar winter stratospheric vortex is a coherent structure that undergoes different types of deformation that can be revealed by the geometric invariant moments. Three moments are used—the aspect ratio, the centroid latitude, and the area of the vortex based on stratospheric data from the 40-yr ECMWF Re-Analysis (ERA-40) project—to study sudden stratospheric warmings. Hierarchical clustering combined with data image visualization techniques is used as well. Using the gap statistic, three optimal clusters are obtained based on the three geometric moments considered here. The 850-K potential vorticity field, as well as the vertical profiles of polar temperature and zonal wind, provides evidence that the clusters represent, respectively, the undisturbed (U), displaced (D), and split (S) states of the polar vortex. This systematic method for identifying and characterizing the state of the polar vortex using objective methods is useful as a tool for analyzing observations and as a test for climate models to simulate the observations. The method correctly identifies all previously identified major warmings and also identifies significant minor warmings where the atmosphere is substantially disturbed but does not quite meet the criteria to qualify as a major stratospheric warming.

Relation between the 100-hPa Heat Flux and Stratospheric Potential Vorticity

Abstract It is shown that a quantitative relation exists between the stratospheric polar cap potential vorticity and the 100-hPa eddy heat flux. A difference in potential vorticity between years is found to be linearly related to the flux difference integrated over time, taking into account a decrease in relaxation time scale with height in the atmosphere. This relation (the PV–flux relation) is then applied to the 100-hPa flux difference between 2008/09 and the climatology (1989–2008) to obtain a prediction of the polar cap potential vorticity difference between the 2008/09 winter and the climatology. A prediction of the 2008/09 polar cap potential vorticity is obtained by adding this potential vorticity difference to the climatological potential vorticity. The observed polar cap potential vorticity for 2008/09 shows a large and abrupt change in the potential vorticity in midwinter, related to the occurrence of a major sudden stratospheric warming in January 2009; this is also captured by the potential vorticity predicted from the 100-hPa flux and the PV–flux relation. The results of the mean PV–flux relation show that, on average, about 50% of the interannual variability in the state of the Northern Hemisphere stratosphere is determined by the variations in the 100-hPa heat flux. This explained variance can be as large as 80% for more severe events, as demonstrated for the 2009 major warming.

Predicted effects of climate warming on the distribution of 50 stream fishes in Wisconsin, U.S.A.

Summer air and stream water temperatures are expected to rise in the state of Wisconsin, U.S.A., over the next 50 years. To assess potential climate warming effects on stream fishes, predictive models were developed for 50 common fish species using classification-tree analysis of 69 environmental variables in a geographic information system. Model accuracy was 56·0-93·5% in validation tests. Models were applied to all 86 898 km of stream in the state under four different climate scenarios: current conditions, limited climate warming (summer air temperatures increase 1° C and water 0·8° C), moderate warming (air 3° C and water 2·4° C) and major warming (air 5° C and water 4° C). With climate warming, 23 fishes were predicted to decline in distribution (three to extirpation under the major warming scenario), 23 to increase and four to have no change. Overall, declining species lost substantially more stream length than increasing species gained. All three cold-water and 16 cool-water fishes and four of 31 warm-water fishes were predicted to decline, four warm-water fishes to remain the same and 23 warm-water fishes to increase in distribution. Species changes were predicted to be most dramatic in small streams in northern Wisconsin that currently have cold to cool summer water temperatures and are dominated by cold-water and cool-water fishes, and least in larger and warmer streams and rivers in southern Wisconsin that are currently dominated by warm-water fishes. Results of this study suggest that even small increases in summer air and water temperatures owing to climate warming will have major effects on the distribution of stream fishes in Wisconsin.

Case studies of the mesospheric response to recent minor, major, and extended stratospheric warmings

We have studied the mesospheric response to two recent stratospheric warmings by performing short‐term forecasts at medium (1.5°) and high (0.5°) spatial resolution under different gravity wave drag (GWD) scenarios. We validated our models with our high‐altitude analysis that extends from 0 to 90 km. For the minor warming of January 2008, reduced upper‐level orographic GWD weakened the downward residual circulation and cooled the mesosphere. Parameterized nonorographic GWD increased the simulated mesospheric cooling. For the prolonged major warming of 2006, heavily attenuated orographic GWD led to pronounced cooling near 50 km. During the extended phase of this event, an unusually strong westerly polar vortex reformed in the lower mesosphere, which allowed westward propagating nonorographic gravity waves to reach the mesosphere and break, with net westward accelerations of over 50 m s−1 d−1. This, in turn, forced a strong residual circulation, yielding descent velocities over 2 cm s−1 between 65°N and 85°N, consistent with previous reports of enhanced downward transport of trace constituents. The resulting adiabatic heating, as evidenced by the unusually vertically displaced stratopause at 80 km, is likely a direct consequence of this enhanced gravity wave driven descent. High‐resolution simulations without parameterized GWD were closer to the analysis than medium‐resolution simulations with parameterized orographic GWD only, but still did not fully simulate the mesospheric thermal response. Specifically, the 80 km temperature enhancement was still underestimated in these simulations. This suggests that higher spatial resolution is needed to adequately resolve extratropical gravity wave momentum fluxes.

Aura Microwave Limb Sounder observations of dynamics and transport during the record‐breaking 2009 Arctic stratospheric major warming

A major stratospheric sudden warming (SSW) in January 2009 was the strongest and most prolonged on record. Aura Microwave Limb Sounder (MLS) observations are used to provide an overview of dynamics and transport during the 2009 SSW, and to compare with the intense, long‐lasting SSW in January 2006. The Arctic polar vortex split during the 2009 SSW, whereas the 2006 SSW was a vortex displacement event. Winds reversed to easterly more rapidly and reverted to westerly more slowly in 2009 than in 2006. More mixing of trace gases out of the vortex during the decay of the vortex fragments, and less before the fulfillment of major SSW criteria, was seen in 2009 than in 2006; persistent well‐defined fragments of vortex and anticyclone air were more prevalent in 2009. The 2009 SSW had a more profound impact on the lower stratosphere than any previously observed SSW, with no significant recovery of the vortex in that region. The stratopause breakdown and subsequent reformation at very high altitude, accompanied by enhanced descent into a rapidly strengthening upper stratospheric vortex, were similar in 2009 and 2006. Many differences between 2006 and 2009 appear to be related to the different character of the SSWs in the two years.

HOCl chemistry in the Antarctic Stratospheric Vortex 2002, as observed with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

Abstract. In the 2002 Antarctic polar vortex enhanced HOCl mixing ratios were detected by the Michelson Interferometer for Passive Atmospheric Sounding both at altitudes of around 35 km (1000 K potential temperature), where HOCl abundances are ruled by gas phase chemistry and at around 18–24 km (475–625 K), which belongs to the altitude domain where heterogeneous chlorine chemistry is relevant. At altitudes of 33 to 40 km polar vortex HOCl mixing ratios were found to be around 0.14 ppbv as long as the polar vortex was intact, centered at the pole, and thus received relatively little sunlight. This is the altitude region where in midlatitudinal and tropic atmospheres peak HOCl mixing ratios significantly above 0.2 ppbv (in terms of daily mean values) are observed. After deformation and displacement of the polar vortex in the course of a major warming, ClO-rich vortex air was more exposed to sunlight, where enhanced HOx abundances led to largely increased HOCl mixing ratios (up to 0.3 ppbv), exceeding typical midlatitudinal and tropical amounts significantly. The HOCl increase was preceded by an increase of ClO. Model runs could reproduce these measurements only when the Stimpfle et al. (1979) rate constant for the reaction ClO+HO2→HOCl+O2 was used but not with the current JPL recommendation. At an altitude of 24 km, HOCl mixing ratios of up to 0.15 ppbv were detected. This HOCl enhancement, which is already visible in 18 September data, is attributed to heterogeneous chemistry, which is in agreement with observations of polar stratospheric clouds. The measurements were compared to a model run where no polar stratospheric clouds appeared during the observation period. The fact that HOCl still was produced in the model run suggests that a significant part of HOCl was generated from ClO rather than directly via heterogeneous reaction. Excess ClO, lower ClONO2 and earlier loss of HOCl in the measurements are attributed to ongoing heterogeneous chemistry which is not reproduced by the model. On 11 October, polar vortex mean daytime mixing ratios were only 0.03 ppbv.

Rayleigh lidar observations of enhanced stratopause temperature over Gadanki (13.5° N, 79.2° E) during major stratospheric warming in 2006

Abstract. Rayleigh lidar observations of temperature structure and gravity wave activity were carried out at Gadanki (13.5° N, 79.2° E) during January–February 2006. A major stratospheric warming event occurred at high latitude during the end of January and early February. There was a sudden enhancement in the stratopause temperature over Gadanki coinciding with the date of onset of the major stratospheric warming event which occurred at high latitudes. The temperature enhancement persisted even after the end of the high latitude major warming event. During the same time, the UKMO (United Kingdom Meteorological Office) zonal mean temperature showed a similar warming episode at 10° N and cooling episode at 60° N around the region of stratopause. This could be due to ascending (descending) motions at high (low) latitudes above the critical level of planetary waves, where there was no planetary wave flux. The time variation of the gravity wave potential energy computed from the temperature perturbations over Gadanki shows variabilities at planetary wave periods, suggesting a non-linear interaction between gravity waves and planetary waves. The space-time analysis of UKMO temperature data at high and low latitudes shows the presence of similar periodicities of planetary wave of zonal wavenumber 1.

Variation of Sea Ice Temperature from CHINARE 2003 and Its Application on Sea Ice Model Evaluation

AbstractVariation of vertical profiles of sea ice temperature and adjacent atmosphere and ocean temperatures were measured by ice drifting buoys deployed in the northeast Chukchi Sea as part of the 2003 Chinese Arctic Research Expedition. The buoy observations (September 2003 to February 2005) show that the cooling of the ice began in late September, propagated down through the ice, reaching the bottom of the ice in December, and continued throughout the winter. In winter 2003/04, some obvious warmings were observed in the upper portion of the ice in response to major warmings in the overlying atmosphere associated with the periodicity of storms in the northeast Chukchi Sea. It is found that the melt season at the buoy site in 2004 was about 15% longer than normal. The buoy observed vertical ice temperature profiles were used as a diagnostic for sea ice model evaluation. The results show that the simulated ice temperature profiles have large discrepancies as compared with the observations.

Interannual-to-decadal variability of the stratosphere during the 20th century: ensemble simulations with a chemistry-climate model

Abstract. Interannual-to-decadal variability in stratospheric ozone and climate have a number of common sources, such as variations in solar irradiance, stratospheric aerosol loading due to volcanic eruptions, El Niño Southern Oscillation variability and the quasi-biennial oscillation (QBO). Currently available data records as well as model simulations addressing stratospheric chemical climate variability mostly cover only the past few decades, which is often insufficient to address natural interannual-to-decadal variability. Here we make use of recently reconstructed and re-evaluated data products to force and validate transient ensemble model simulations (nine members) across the twentieth century computed by means of the chemistry-climate model SOCOL (SOlar Climate Ozone Links). The forcings include sea surface temperatures, sea ice, solar irradiance, stratospheric aerosols, QBO, changes in land properties, greenhouse gases, ozone depleting substances, and emissions of carbon monoxides, and nitrogen oxides. The transient simulations are in good agreement with observations, reconstructions and reanalyses and allow quantification of interannual-to-decadal variability during the 20th century. All ensemble members are able to capture the low-frequency variability in tropical and mid-latitude total ozone as well as in the strength of the subtropical jet, suggesting a realistic response to external forcings in this area. The region of the northern polar vortex exhibits a large internal variability that is found in the frequency, seasonality, and strength of major warmings as well as in the strength of the modeled polar vortex. Results from process-oriented analysis, such as correlation between the vertical Eliassen Palm flux (EP flux) component and polar variables as well as stratospheric ozone trends, are of comparable magnitude to those observed and are consistent in all analysed ensemble members. Yet, trend estimates of the vertical EP flux component vary greatly among ensemble members precluding any robust conclusions. This suggests that internal variability in models must be accounted for in order to quantify the atmospheric model response in wave energy upon external forcings.

Tropical SST Preconditioning of the SH Polar Vortex during Winter 2002

Abstract The response of the Southern Hemisphere (SH) polar atmosphere to the tropical sea surface temperature (SST) during the 2002 winter–spring season is investigated by using a general circulation model (GCM). The SH stratospheric winter of 2002 was particularly unusual, characterized by a weaker-than-normal polar vortex during the whole season. It also registered, at the end of September, the first major warming yet observed in the SH. This event is unexpected in the SH, and it is supposed to be induced by a “preconditioning” of the polar vortex starting at the beginning of the winter. Atmospheric GCM experiments with prescribed SST boundary conditions are performed. The sensitivity of the Antarctic dynamics to the tropical SST of 2002 (a year characterized by an El Niño event of moderate intensity) is studied, and the uniqueness of the 2002 tropical oceanic condition is investigated through the comparison of the simulated response of the climatic system to 2002 and 1997 tropical SST (1997 being a year with a strong El Niño event). Model results highlight a primary role played by the tropical SST of 2002 in the development of the peculiar characteristics of the Antarctic dynamics during the winter months that appears to be a necessary condition for the generation of the anomalous destabilization of the polar vortex during the following spring. Results for June 2002 show a strong generation of vertically propagating waves resulting from the tropical SST that, through the perturbation of the westerly jet at middle latitudes, produces a preconditioning of the polar vortex by affecting the wave refraction index. The particular structure of the tropical SST anomalies during the winter of 2002 is thought to have influenced the subsequent preconditioning of the stratospheric vortex.

Relationships between interannual variations in stratospheric warmings, tropospheric circulation, and sea surface temperature in the Northern Hemisphere

The leading modes of interannual and long-term variations in the stratospheric and tropospheric circulation and total ozone (TOMS data) and their relations to Northern Hemisphere sea surface temperature (SST) anomalies are investigated using the monthly mean NCEP/NCAR reanalysis data for the winter months of 1958–2003. Strong correlations are indicated between the interannual total ozone variations over Labrador and the North Atlantic and changes in the stratospheric polar vortex. The onset of major stratospheric warmings is connected not only with the strengthening of westerlies at the 500-hPa level in the midlatitude Atlantic, but also with the weakening of tropospheric winds over the north of eastern Siberia and strengthening over the Far East. In years with major stratospheric warmings, abnormally cold winters are observed in Eurasia, especially in eastern Siberia and northeastern China. The calculated simultaneous (with no time lags) correlations of the stratospheric circulation changes with El Nino/La Nina events give evidence of low correlations between the tropical Pacific SST anomalies and the stratospheric dynamics in the Arctic. However, there are high correlations of the extratropical Pacific and Atlantic SST anomalies with interannual tropospheric and stratospheric circulation variations, the stratospheric dynamics being more strongly connected with Pacific SST than with Atlantic SST anomalies. The interannual changes in tropospheric circulation are coupled to SST anomalies in both the Pacific and the Atlantic. Mechanisms of long-term changes in the interactive ocean-atmosphere-ozone layer system are discussed.

The evolution of the stratopause during the 2006 major warming: Satellite data and assimilated meteorological analyses

Microwave Limb Sounder and Sounding of the Atmosphere with Broadband Emission Radiometry data provide the first opportunity to characterize the four‐dimensional stratopause evolution throughout the life‐cycle of a major stratospheric sudden warming (SSW). The polar stratopause, usually higher than that at midlatitudes, dropped by ∼30 km and warmed during development of a major “wave 1” SSW in January 2006, with accompanying mesospheric cooling. When the polar vortex broke down, the stratopause cooled and became ill‐defined, with a nearly isothermal stratosphere. After the polar vortex started to recover in the upper stratosphere/lower mesosphere (USLM), a cool stratopause reformed above 75 km, then dropped and warmed; both the mesosphere above and the stratosphere below cooled at this time. The polar stratopause remained separated from that at midlatitudes across the core of the polar night jet. In the early stages of the SSW, the strongly tilted (westward with increasing altitude) polar vortex extended into the mesosphere, and enclosed a secondary temperature maximum extending westward and slightly equatorward from the highest altitude part of the polar stratopause over the cool stratopause near the vortex edge. The temperature evolution in the USLM resulted in strongly enhanced radiative cooling in the mesosphere during the recovery from the SSW, but significantly reduced radiative cooling in the upper stratosphere. Assimilated meteorological analyses from the European Centre for Medium‐Range weather Forecasts (ECMWF) and Goddard Earth Observing System Version 5.0.1 (GEOS‐5), which are not constrained by data at polar stratopause altitudes and have model tops near 80 km, could not capture the secondary temperature maximum or the high stratopause after the SSW; they also misrepresent polar temperature structure during and after the stratopause breakdown, leading to large biases in their radiative heating rates. ECMWF analyses represent the stratospheric temperature structure more accurately, suggesting a better representation of vertical motion; GEOS‐5 analyses more faithfully describe stratopause level wind and wave amplitudes. The high‐quality satellite temperature data used here provide the first daily, global, multiannual data sets suitable for assessing and, eventually, improving representation of the USLM in models and assimilation systems.

Anomalous quasi-stationary planetary waves over the Antarctic region in 1988 and 2002

Abstract. Anomalies in the Antarctic total ozone and amplitudes of the quasi-stationary planetary waves in the lower stratosphere temperature during the winter and spring of 1988 and 2002 have been compared. Westward displacement of the quasi-stationary wave (QSW) extremes by 50°–70° relative to the preceding years of the strong stratospheric polar vortex in 1987 and 2001, respectively, was observed. A dependence of the quasi-stationary wave ridge and trough positions on the strength of the westerly zonal wind in the lower stratosphere is shown. Comparison of the QSW amplitude in the lower stratosphere temperature in July and August shows that the amplitude distribution with latitude in August could be considered as a possible indication of the future anomalous warming in Antarctic spring. In August 2002, the QSW amplitude of 10 K at the edge region of the polar vortex (60° S–65° S) preceded the major warming in September, whereas in August 1988, the highest 7 K amplitude at 55° S preceded the large warming in the next months. These results suggest that the peak value of the lower stratosphere temperature QSW amplitude and the peak latitudinal position in late winter can influence the southern polar vortex strength in spring.

Examination of the 2002 major warming in the southern hemisphere using ground-based and Odin/SMR assimilated data: stratospheric ozone distributions and tropic/mid-latitude exchange

Following an exceptionally active winter, the 2002 Southern Hemisphere (SH) major warming occurred in late September. It was preceded by three minor warming events that occurred in late August and early September, and yielded vortex split and break-down over Antarctica. Ozone (O3 and nitrous oxide (N2O) profiles obtained during that period of time (15 August – 4 October) by the Sub-Millimetre Radiometer (SMR) aboard the Odin satellite are assimilated into MOCAGE (Modélisation Isentrope du transport Mésoéchelle de l'Ozone Stratosphérique par Advection), a global three-dimensional chemistry transport model of Météo-France. The assimilated algorithm is a three-dimensional-FGAT built by the European Centre for Research and Advance Training in Scientific Computation (CERFACS) using the PALM (Projet d'Assimilation par Logiciel Multi-méthode) software. The assimilated O3 and N2O profiles and isentropic distributions are compared to ground-based measurements (LIDAR and balloon-sonde) and to maps of advected potential vorticity (APV). The latter is computed by the MIMOSA (Modélisation Isentrope du transport Mésoéchelle de l'Ozone Stratosphérique par Advection) model, a high-resolution advection transport model, using meteorological fields from the European Centre for Medium-Range Weather Forecasts (ECMWF). It is found that O3 concentrations retrieved by the MOCAGE–PALM assimilation system show a reasonably good agreement in the 20–28 km height range when compared with ground-based profiles. This altitude range corresponds to the intersection between the MOCAGE levels (0–28 km) and SMR O3 retrievals (20–50 km). Moreover, comparison of N2O assimilated fields with MIMOSA APV maps indicates that the dramatic split and subsequent break-down of the polar vortex, as well as the associated mixing of mid- and low-latitude stratospheric air, are well resolved and pictured by MOCAGE–PALM. The present study demonstrates also that the tremendous dynamics and associated polar vortex deformations during the 2002-austral-winter have modified ozone and nitrous oxide distributions not only at the vicinity of the polar vortex, but over topics and subtropics as well. PACS Nos.: 92.60.H–, 92.60.Hd, 92.70.Cp, 92.70.Gt

Polar mesosphere and lower thermosphere dynamics: 2. Response to sudden stratospheric warmings

The dynamical response of the polar mesosphere and lower thermosphere (MLT) to sudden stratospheric warmings is investigated using MF radars at Davis (69°S, 78°E), Syowa (69°S, 40°E) and Rothera (68°S, 68°W) in the Antarctic and Poker Flat (65°N, 147°W) and Andenes (69°N, 16°E) in the Arctic. Mean winds, gravity waves and planetary waves are investigated during sudden stratospheric warmings, and comparisons are made with climatological means. The available MF radar data set includes six major sudden stratospheric warmings in the Northern Hemisphere and the unprecedented 2002 Southern Hemisphere major stratospheric warming. Three of the six northern events are relatively weak and could almost be classed as minor warmings, while the larger three have similar characteristics to the event in the Southern Hemisphere. Zonal wind reversals associated with the major warmings in both hemispheres are generally weaker and earlier by several days in the mesosphere than in the stratosphere. There are, however, significant differences between locations in their response to stratospheric warmings. The zonal winds are remarkably weaker than average during both winter and spring around the time of the southern major warming of 2002, but these effects are not observed for the Northern Hemisphere events. Gravity wave activity is found to vary significantly between individual stratospheric warming events and also between individual locations.

Lateglacial and early Holocene climatic oscillations on the western Svalbard margin, European Arctic

A multi proxy sediment core record on the continental margin off western Svalbard, European Arctic, reflects large climatic and oceanographic oscillations at the Lateglacial–early Holocene transition. Based on studies of planktonic foraminifera, their stable oxygen and carbon isotopic composition and ice rafted debris, we have reconstructed the last 14 cal. ka BP. The period 14–13.5 cal. ka BP was characterized by highly unstable climatic conditions. Short-lived episodes of warming alternated with meltwater pulses and enhanced iceberg rafting. This period correlates to a regional warming of the northern North Atlantic. An overall decrease in meltwater took place during the deglaciation (14–10.8 cal. ka BP). The late Younger Dryas and subsequent transition into the early Holocene is characterized by a reduced flux of planktonic foraminifera and increased iceberg rafting. A major warming took place from 10.8 to 9.7 cal. ka BP, the influence of meltwater ceased and the flux of warm Atlantic Water increased. From 9.7 to 8.8 cal. ka BP, the western Svalbard margin surface waters were significantly warmer than today. This warm period, the thermal maximum, was followed by an abrupt cooling at 8.8. cal. ka BP, caused by an increased influence of Arctic Water from the Arctic Ocean. The results document that the European Arctic was very sensitive to climatic and oceanographic changes at the end of the last glacial and during the Holocene.

Ozone loss driven by nitrogen oxides and triggered by stratospheric warmings can outweigh the effect of halogens

Ozone loss in the lower and middle stratosphere in spring and summer, in particular over polar regions, is driven mainly by halogens and nitrogen oxides (NOx). Whereas the stratospheric chlorine levels are expected to decrease in the future, the role of NOx for the O3 budget in a changing climate is not well quantified. Here we combine satellite measurements and model simulations to diagnose the accumulated O3 loss during winter and spring 2002–2003 in the Arctic polar stratosphere. We show that in a winter stratosphere strongly disturbed by warmings, O3 loss processes driven by halogens and NOx can significantly overlap within the polar column and become comparable in magnitude even if a significant, halogen‐induced O3 loss has occurred. Whereas, until the beginning of March 2003, polar column O3 loss was mainly caused by the halogen chemistry within the vortex at an altitude around 18 km, the chemical O3 destruction in March and April was dominated by the NOx chemistry in O3‐rich air masses transported from the subtropics and mixed with the polar air above the region affected by the halogens. This NOx‐related O3 loss started around mid‐December 2002 in subtropical air masses above 30 km that moved poleward after the major warming in January, descended to 22 km with an increasing magnitude of O3 loss and reached surprisingly high values of up to 50% local loss around the end of April. To some extent, the NOx‐driven O3 loss was enhanced by mesospheric air trapped in the vortex at the beginning of the winter as a layer of few km in the vertical and transported downward within the vortex. The effect of NOx transported from the subtropics dominated the O3 loss processes in the polar stratosphere in spring 2003, both relative to the effect of the halogens and relative to the contribution of the mesospheric NOx sources. A comparison with the 1999/2000 Arctic winter and with the Antarctic vortex split event in 2002 shows that wave events triggered by stratospheric warmings may significantly enhance O3 loss driven by NOx when O3‐ and NOx‐rich air masses from the subtropics are transported poleward and are mixed with the vortex air.