Major Sudden Stratospheric Warming Research Articles

Aura Microwave Limb Sounder observations of the Northern Annular Mode: From the mesosphere to the upper troposphere

Vertical structure and evolution of the wintertime Northern Hemisphere Annular Mode (NAM), the first Empirical Orthogonal Function (EOF) of geopotential height anomalies, are constructed from the 2005–2009 Aura Microwave Limb Sounder (MLS) measurements in the entire middle atmosphere between 316 hPa (∼9 km) and 0.001 hPa (∼90 km). This is the first report of NAM structure extending into the mesosphere. The mode appears to be robust and it accounts for up to 70% of middle‐atmospheric variance before decreasing in the upper mesosphere. The vertical connection of the NAM modes suggests strong dynamic coupling between the mesosphere and stratosphere. Time evolution of the NAM suggests that the significant NAM anomalies typically appear first in the mesosphere and progress downward. NAM patterns derived from MLS observations are consistent with those derived from long‐term reanalysis below the middle stratosphere. The NAM indexes show the mesospheric cooling signals during the major stratospheric sudden warmings (SSWs) in 2006 and 2009.

Ozone depletion, water vapor increase, and PSC generation at midlatitudes by the 2008 major stratospheric warming

The ground‐based microwave radiometers GROMOS and MIAWARA at Bern (Switzerland) continuously measure ozone and water vapor profiles from 20 to 70 km altitude. A major sudden stratospheric warming occurred around 19 February 2008 with minimal temperatures of 189 K at 40 hPa and maximal temperatures of 300 K at 4 hPa. During the stratospheric warming the Swiss ground‐based radiometers observed a depletion of ozone and an enhancement of water vapor while NASA's CALIPSO satellite instrument measured a large PSC area over Europe. Ozone depletion in the lower stratosphere is explained by transport of ozone poor air from the cold polar vortex. The depletion of upper stratospheric ozone is caused by a sudden temperature increase of about 50 K. A simulation of a chemical box model confirms that a major fraction of the observed decrease of the ozone mixing ratio at 4 hPa can be explained by the effect of the increasing temperature on the ozone chemistry. The chemical ozone destruction is dominated by a catalytic NOx cycle, which is more efficient at higher temperatures. The water vapor enhancement can be explained by transport processes. The rather unusual occurrence of a PSC and a sudden stratospheric warming at midlatitudes suggest that further monitoring of the Earth's middle atmosphere is required for the timely detection of unexpected problems due to ozone loss and climate change.

Satellite observations and modeling of transport in the upper troposphere through the lower mesosphere during the 2006 major stratospheric sudden warming

Abstract. An unusually strong and prolonged stratospheric sudden warming (SSW) in January 2006 was the first major SSW for which globally distributed long-lived trace gas data are available covering the upper troposphere through the lower mesosphere. We use Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) data, the SLIMCAT Chemistry Transport Model (CTM), and assimilated meteorological analyses to provide a comprehensive picture of transport during this event. The upper tropospheric ridge that triggered the SSW was associated with an elevated tropopause and layering in trace gas profiles in conjunction with stratospheric and tropospheric intrusions. Anomalous poleward transport (with corresponding quasi-isentropic troposphere-to-stratosphere exchange at the lowest levels studied) in the region over the ridge extended well into the lower stratosphere. In the middle and upper stratosphere, the breakdown of the polar vortex transport barrier was seen in a signature of rapid, widespread mixing in trace gases, including CO, H2O, CH4 and N2O. The vortex broke down slightly later and more slowly in the lower than in the middle stratosphere. In the middle and lower stratosphere, small remnants with trace gas values characteristic of the pre-SSW vortex lingered through the weak and slow recovery of the vortex. The upper stratospheric vortex quickly reformed, and, as enhanced diabatic descent set in, CO descended into this strong vortex, echoing the fall vortex development. Trace gas evolution in the SLIMCAT CTM agrees well with that in the satellite trace gas data from the upper troposphere through the middle stratosphere. In the upper stratosphere and lower mesosphere, the SLIMCAT simulation does not capture the strong descent of mesospheric CO and H2O values into the reformed vortex; this poor CTM performance in the upper stratosphere and lower mesosphere results primarily from biases in the diabatic descent in assimilated analyses.

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.

Dynamical response of low-latitude middle atmosphere to major sudden stratospheric warming events

The zonally averaged UK Meteorological Office (UKMO) zonal mean temperature and zonal winds for the latitudes 8.75°N and 60°N are used to investigate the low-latitude dynamical response to the high latitude sudden stratospheric warming (SSW) events that occurred during winter of the years 1998–1999, 2003–2004 and 2005–2006. The UKMO zonal mean zonal winds at 60°N show a short-term reversal to westward winds in the entire upper stratosphere and lower mesosphere and the low-latitude winds (8.75°N) show enhanced eastward flow in the upper stratosphere and strong westward flow in the lower mesosphere during the major SSW events at high latitudes. The mesosphere and lower thermosphere (MLT) zonal winds acquired by medium frequency (MF) radar at Tirunelveli (8.7°N, 77.8°E) show a change of wind direction from eastward to westward several days before the onset of SSW events and these winds decelerate and weak positive (eastward) winds prevail during the SSW events. The time variation of zonal winds over Tirunelveli is nearly similar to the one reported from high latitudes, except that the latter shows intense eastward winds during the SSW events. Besides, the comparison of daily mean meridional winds over Tirunelveli with those over Collm (52°N, 15°E) show that large equatorial winds are observed over Tirunelveli during the 2005–2006 event and over Collm during the 1998–1999 events. The variable response of MLT dynamics to different SSW events may be explained by the variability of gravity waves.

Planetary and gravity waves in the mesosphere and lower thermosphere region over Tirunelveli (8.7°N, 77.8°E) during stratospheric warming events

An investigation of planetary wave (PW) activities in UKMO (UK Meteorological Office) winds during winter of the years 1998–99 and 2005–06, when major sudden stratospheric warming (SSW) events occurred, shows that the amplitude of PW of zonal wave number 1 is considerably reduced in zonal winds, when the warming event is onset and the reduced activity persists several days even after the end of the SSW event. Similar reduction of PW activity in zonal winds has been observed in the wavelet spectrum of MF radar zonal winds at altitudes 84–98 km over Tirunelveli (8.7°N, 77.8°E). During this period of reduced PW activity, enhancement in gravity wave activity is observed during 2005–06 and is not observed during 1998–99 and the mean meridional winds change to more equatorward during 2005–06 and remain poleward during 1998–99. In accordance with TIME‐GCM results, our observations show that the wind reversal occurred in the stratosphere during major warming events allows more eastward gravity waves to propagate into the mesosphere and lower thermosphere (MLT) region, which causes changes in the meridional circulation from poleward to equatorward.

Nonmigrating tidal activity related to the sudden stratospheric warming in the Arctic winter of 2003/2004

Abstract. This paper is focused on the nonmigrating tidal activity seen in the SABER/TIMED temperatures that is related to the major sudden stratospheric warming (SSW) taking place in the Arctic winter of 2003/2004. The emphasis is on the nonmigrating diurnal tides observed in the stratosphere and lower mesosphere which is usually accepted to be insignificant in comparison with that in the upper mesosphere and thermosphere. By using different independent spectral methods we found a significant amplification in December–January of the following nonmigrating 24-h tides: zonally symmetric (s=0), eastward propagating with zonal wavenumber 1 (E1), and westward propagating with zonal wavenumbers 2 and 3 (W2 and W3) tides. It has been found that the double peak nonmigrating tidal amplifications located in the stratosphere (~40 km) and in the lower mesosphere (~70 km) are a consequence of the maintained hydrostatic relation. By detailed comparison of the evolution and spatial structure of the nonmigrating diurnal tides with those of the migrating diurnal tide and stationary planetary waves (SPWs) evidence for a SPW-migrating tide interaction as a source of nonmigrating tides has been presented. Therefore, the nonmigrating 24-h tides turn out to be an important component of the middle atmosphere dynamics during the major SSW in the Arctic winter of 2003/2004.

Planetary Wave Breaking and Tropospheric Forcing as Seen in the Stratospheric Sudden Warming of 2006

Abstract The major stratospheric sudden warming (SSW) of January 2006 is examined using meteorological fields from Goddard Earth Observing System version 4 (GEOS-4) analyses and forecast fields from the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics, High Altitude (NOGAPS-ALPHA). The study focuses on the upper tropospheric forcing that led to the major SSW and the vertical structure of the subtropic wave breaking near 10 hPa that moved low tropical values of potential vorticity (PV) to the pole. Results show that an eastward-propagating upper tropospheric ridge over the North Atlantic with its associated cold temperature perturbations (as manifested by high 360-K potential temperature surface perturbations) and large positive local values of meridional heat flux directly forced a change in the stratospheric polar vortex, leading to the stratospheric subtropical wave breaking and warming. Results also show that the anticyclonic development, initiated by the subtropical wave breaking and associated with the poleward advection of the low PV values, occurred over a limited altitude range of approximately 6–10 km. The authors also show that the poleward advection of this localized low-PV anomaly was associated with changes in the Eliassen–Palm (EP) flux from equatorward to poleward, suggesting an important role for Rossby wave reflection in the SSW of January 2006. Similar upper tropospheric forcing and subtropical wave breaking were found to occur prior to the major SSW of January 2003.

Modulations in the planetary wave field induced by upward‐propagating Rossby wave packets prior to stratospheric sudden warming events: A case‐study

AbstractA diagnostic framework is introduced in which anomalous zonally averaged Rossby wave‐activity injection into the stratosphere is decomposed into a contribution solely from zonally confined upward‐propagating Rossby wave packets and another from interaction of the wave packets with the climatological planetary waves. To pinpoint the tropospheric sources of the wave packets, a particular form of wave‐activity flux is evaluated for the associated circulation anomalies. The framework is applied to reanalysis data for the period prior to a stratospheric sudden warming (SSW) event in January 2006, which was associated with two successive events of above‐normal wave‐activity injection from the troposphere. In the earlier event, a pair of wave packets that emanated from tropospheric anomalies over the North Pacific and over Europe enhanced the upward wave‐activity injection, which was augmented further by their interaction with the climatological planetary wave. In contrast, in the later period a wave packet that emanated from an anticyclonic anomaly over the North Atlantic is found to be the primary contributor to the enhanced planetary wave‐activity injection, while its interaction with the climatological planetary wave contributed negatively. The predominant importance of the sole contribution from a single wave packet is also found in a major SSW event observed over Antarctica in September 2002. These results indicate that the diagnostic framework presented in this study is a useful tool for understanding the interaction between anomalies associated with zonally confined wave packets and climatological‐mean planetary waves in the study of stratosphere‐‐troposphere dynamical coupling. Copyright © 2009 Royal Meteorological Society

Planetary waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003/2004

The vertical coupling of the stratosphere‐mesosphere system through quasi‐stationary and traveling planetary waves during the major sudden stratospheric warming (SSW) in the Arctic winter of 2003/2004 has been studied using three types of data. The UK Met Office (UKMO) assimilated data set was used to examine the features of the global‐scale planetary disturbances present in the winter stratosphere of the Northern Hemisphere. Sounding the Atmosphere using Broadband Emission Radiometry (SABER) satellite measurements were used as well for extracting the stationary planetary waves in the zonal and meridional winds of the stratosphere and mesosphere. Radar measurements at eight stations, four of them situated at high latitudes (63–69°N) and the other four at midlatitudes (52–55°N) were used to determine planetary waves in the mesosphere‐lower thermosphere (MLT). The basic results show that prior to the SSW, the stratosphere‐mesosphere system was dominated by an upward and westward propagating ∼16‐day wave detected simultaneously in the UKMO and MLT zonal and meridional wind data. After the onset of the SSW, longer‐period (∼22–24 days) oscillations were observed in the zonal and meridional MLT winds. These likely include the upward propagation of stationary planetary waves from below and in situ generation of disturbances by the dissipation and breaking of gravity waves filtered by stratospheric winds.

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.

Decadal‐scale changes in the effect of the QBO on the northern stratospheric polar vortex

This study documents decadal‐scale changes in the Holton and Tan (HT) relationship, i.e., the influence of the lower stratospheric equatorial quasi‐biennial oscillation (QBO) on the northern hemisphere (NH) extratropical circulation. Using a combination of ECMWF ERA‐40 Reanalysis and Operational data from 1958–2006, we find that the Arctic stratosphere is indeed warmer under easterly QBO and colder under westerly QBO. During November to January, composite easterly minus westerly QBO signals in zonal wind extend from the lower stratosphere to the upper stratosphere and are centered at ∼5 hPa, 55–65°N with a magnitude of ∼10 m s−1. In temperature, the maximum signal is near ∼20–30 hPa at the pole with a magnitude of ∼4 K. During winter, the dominant feature is a poleward and downward transfer of wind and temperature anomalies from the midlatitude upper stratosphere to the high latitude lower stratosphere. For the first time, a statistically significant decadal scale change of the HT relationship during 1977–1997 is diagnosed. The main feature of the change is that the extratropical QBO signals reverse sign in late winter, resulting in fewer and delayed major stratospheric sudden warmings (SSWs), which occurred more often under westerly QBO. Consistent with earlier studies, it is found that the HT relationship is significantly stronger under solar minima overall, but the solar cycle does not appear to be the primary cause for the detected decadal‐scale change. Possible mechanisms related to changes in planetary wave forcing are discussed.

Is There a Statistical Connection between Stratospheric Sudden Warming and Tropospheric Blocking Events?

Abstract This paper presents statistical analyses of possible associations between major stratospheric sudden warming (SSW) and tropospheric blocking events in the Northern Hemisphere (NH) with 49 yr of NCEP–NCAR reanalysis data from 1957/58 to 2005/06. Using a random shuffling or “bootstrap” method, these analyses explore two hypotheses claiming that blocking events occur preferentially and last longer in association with SSWs (pre- and post-SSW periods are considered separately). In the shuffling method, the defined SSWs are randomly redistributed to evaluate the statistical significance of linked cases in the original data. The author’s analyses generally do not support either hypothesis for the pre- or post-SSW period when treating the SSW events all together, suggesting that such associations are not dominant modes of coupling.

The relationship between the occurrence rate of major stratospheric warmings and solar Lyman‐alpha flux

The statistical connection between major sudden stratospheric warmings (MSSWs) and solar activity was investigated using the Lyman‐alpha flux as a proxy. We subdivided the considered time period between winter 1950‐51 and winter 2006‐07, for which data about MSSWs is available in discrete time intervals of 4 months, and determined the mean Lyman‐alpha flux in them. For the statistical analysis, only those months between December and March, when MSSWs exclusively occurred, were used. Then the range of values of the Lyman‐alpha flux was subdivided into discrete bins of 0.25 × 1011 photons/cm2 s. Next we determined the frequency at which the mean flux values from the chosen months belonged to the subdivided flux intervals. After that we assigned the number of MSSW occurred under the conditions of a certain Lyman‐alpha flux value to the corresponding frequency of the flux values. Finally, we correlated the related MSSW occurrence rate with the discrete Lyman‐alpha flux values. The analysis revealed a significant positive correlation between the 11‐years solar activity and the occurrence rate of the related MSSWs.

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.

Large-scale thermodynamics of the stratosphere and mesosphere during the major stratospheric warming in 2003/2004

The stratosphere–mesosphere response to the major sudden stratospheric warming (SSW) in the winter of 2003/2004 has been studied. The UKMO (UK Meteorological Office) data set was used to examine the features of the large-scale thermodynamic anomalies present in the stratosphere of the Northern Hemisphere. The vertical and latitudinal structure of the genuine anomalies, emphasized by removing the UKMO climatology, has been investigated as well. The features of the stratospheric anomalies have been related to the mesospheric ones in measured neutral winds from radars and temperatures from meteor radars (∼90 km). It was found that the stratospheric warming spread to the lower mesosphere, while cooling occurred in the upper mesosphere, a feature that may be related to the large vertical scales of the stationary planetary waves (SPWs). It was shown also that the beginning of the eastward wind deceleration in the stratosphere–mesosphere system coincided with the maximum amplification of the SPW1 accompanied by short-lived bursts of waves 2 and 3.

Analysis of TOMS‐derived Lambert‐equivalent reflectivities for the period 1996–2002

This study focuses on the analysis of the Lambert‐equivalent reflectivities at 360 nm as acquired by the Total Ozone Mapping Spectrometer (TOMS) instrument on board the Earth Probe satellite, for the period July 1996 to December 2002. The analysis is related to the sudden stratospheric warming (SSW) and the ozone hole split over Antarctic in September 2002. Reflectivities (version 8 TOMS data) were analysed per year, month and day for 2002 and compared to the respective reflectivities of previous years. The low reflectivity values observed in 2002 confirm the absence of polar stratospheric clouds, the latter being a major driving force for the depletion of ozone over the Antarctic; furthermore, they support the occurrence of the reported major SSW. In addition, the Lambert‐equivalent reflectivity values in the year 2002 exhibit an intra‐annual trend that differs from the respective ones in previous years.

Dynamical coupling of the stratosphere and mesosphere in the 2002 Southern Hemisphere major stratospheric sudden warming

NCEP data and a NCAR TIME‐GCM simulation are used to explore the dynamical coupling of the stratosphere and mesosphere during the 2002 Southern Hemisphere major stratospheric sudden warming. The analyses suggest the possibility of feedback interactions between the planetary wave forcing and the mesospheric/stratospheric mean state changes. Multiple strong planetary waves before the warming penetrate into the mesosphere and weaken the polar jet. They alter the wave transmission condition in favor of more upward‐poleward propagation of the wave energy at progressively lower altitudes. The jet reversal and the planetary wave surf zone also descend from the mesosphere down to the stratosphere, making wave breaking more likely at decreasing altitudes with each wave episode. These changes in the wave transmission and breaking conditions in the mesosphere and stratosphere may be critical for the extensive major stratospheric warming.

Tropospheric wave response to decelerated stratosphere seen as downward propagation in northern annular mode

Baldwin and Dunkerton [1999] found that negative northern annular mode (NAM) anomalies sometimes descend all the way from the stratosphere into the lower troposphere. However, no viable mechanism has been proposed so far to account for the magnitude of the anomalies in the denser troposphere. Further, analysis shows that the character of the anomaly changes across the tropopause. Above the tropopause the NAM pattern is approximately zonal, and its descent represents the descent of decelerated zonal mean winds. This stratospheric change is explainable using theories similar to those for the descent of the zero‐wind line associated with a major stratospheric sudden warming. However, such a reversal in the zonal mean wind rarely reaches the denser troposphere. The descent of the NAM anomalies into the troposphere may be implying a different relationship between the stratosphere and the troposphere. We note that in the troposphere the structure of the NAM has a large wave component. In some cases, this wave component appears to react to the decelerated wind configuration aloft. Here we show observations of the wave component and the zonal mean component in comparison to corresponding NAM events to show that the wave response is a sizable component of the NAM anomaly in the troposphere. We will also present a simple model calculation to show that tropospheric waves forced by topography can react to changing stratospheric winds. These tropospheric waves can project directly onto the tropospheric NAM patterns and produce anomalies in the index which appear to be connected to the negative NAM anomalies in the stratosphere.

Enhancement of gravity wave activity observed during a major Southern Hemisphere stratospheric warming by CHAMP/GPS measurements

Using temperature profiles measured by CHAMP/GPS occultations we analyzed the gravity wave activity during the major sudden stratospheric warming (SSW) occurred in the Southern Hemisphere (SH) in late winter/spring of 2002, which for the first time split the polar vortex into two parts. The observed temperatures show a rapid poleward moving increase with a maximum of about 25–30 K with respect to the undisturbed winter conditions, and a reversal of the latitudinal gradients at 30 km and below within 15 days (September 15–30). During this time gravity wave energy (potential energy, Ep) became 3 times higher than usual. This enhancement mostly occurred near the edge and outside the cold polar vortex, but not inside the vortex. We discuss the observed event with potential interaction of gravity waves, planetary waves and the mean circulation during the stratospheric warming.