Major Sudden Stratospheric Warming Research Articles

Interaction between decadal-to-multidecadal oceanic variability and sudden stratospheric warmings.

Major sudden stratospheric warmings (SSWs) are the most important phenomena of the wintertime boreal stratospheric variability. During SSWs, the polar temperature increases abruptly, and easterlies prevail in the stratosphere. Their effects extend farther from the polar stratosphere, affecting near-surface circulation. According to observations, SSWs are not equally distributed in time, with decades experiencing very few events, while others experiencing SSWs almost every winter. Some sources of this SSW multidecadal variability can be traced back to sea surface temperature changes. Here, we investigate the effects of Pacific decadal variability (PDV) and Atlantic multidecadal variability (AMV) on SSWs. We use for the first time a large ensemble of historical experiments to examine the modulation of the frequency, tropospheric precursors, and impact of SSWs by the PDV and AMV. We find a strong impact of the PDV on the occurrence of SSWs, with a higher SSW frequency for the positive phase of the PDV. This PDV influence is mediated by constructive interference of PDV anomalies with tropospheric stationary waves. The main effect of AMV is, instead, a modulation of the tropospheric response to SSWs, a finding that can be useful for predicting the tropospheric fingerprint of SSWs.

HeavyAlpinesnowfall in January 2019 connected to atmospheric blocking

In January 2019, an episode of extreme, record-breaking snowfall hit the northern part of the Alps. The event was linked to persistent North Atlantic blocking, which transported moisture from the North Atlantic towards the Alps. At the same time, the polar vortex was displaced over the North Atlantic, split, and a major sudden stratospheric warming occurred. We discuss the possible role of blocking in the polar vortex split and the onset of the sudden stratospheric warming as well as its implications in predicting the snowfall event.

Eastward‐Propagating Planetary Waves Prior to the January 2009 Sudden Stratospheric Warming

AbstractEastward‐propagating planetary waves (EPWs) were investigated prior to the boreal January 2009 major sudden stratospheric warming (SSW) event simulated by the National Center for Atmospheric Research's Whole Atmosphere Community Climate Model with specified dynamics. About 22 days before SSW onset, a background flow with jet maxima around the upper polar stratosphere and subtropical mesosphere developed due to the net forcing by gravity and planetary waves. The mesospheric wind structure was largely unstable and supported a wave geometry conducive to overreflection. With a zonal phase speed of ∼10 m s−1, EPWs appeared near their turning and critical layers as wavenumber‐2 perturbations in the stratosphere and mesosphere. Accompanied by upward EPW activity from the lower stratosphere, EPW growth exhibited characteristics of wave instability and overreflection.

The 2019 Southern Hemisphere Stratospheric Polar Vortex Weakening and Its Impacts

AbstractThis study offers an overview of the low-frequency (i.e., monthly to seasonal) evolution, dynamics, predictability, and surface impacts of a rare Southern Hemisphere (SH) stratospheric warming that occurred in austral spring 2019. Between late August and mid-September 2019, the stratospheric circumpolar westerly jet weakened rapidly, and Antarctic stratospheric temperatures rose dramatically. The deceleration of the vortex at 10 hPa was as drastic as that of the first-ever-observed major sudden stratospheric warming in the SH during 2002, while the mean Antarctic warming over the course of spring 2019 broke the previous record of 2002 by ∼50% in the midstratosphere. This event was preceded by a poleward shift of the SH polar night jet in the uppermost stratosphere in early winter, which was then followed by record-strong planetary wave-1 activity propagating upward from the troposphere in August that acted to dramatically weaken the polar vortex throughout the depth of the stratosphere. The weakened vortex winds and elevated temperatures moved downward to the surface from mid-October to December, promoting a record strong swing of the southern annular mode (SAM) to its negative phase. This record-negative SAM appeared to be a primary driver of the extreme hot and dry conditions over subtropical eastern Australia that accompanied the severe wildfires that occurred in late spring 2019. State-of-the-art dynamical seasonal forecast systems skillfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative SAM from as early as late July.

Statistical Characteristics and Long-Term Variations of Major Sudden Stratospheric Warming Events

Using NCEP/NCAR reanalysis data, we investigate the statistical characteristics and the long-term variations of major sudden stratospheric warming (SSW) events in the Northern Hemisphere. We find that the strength and duration of major SSW events has increased from 1958 to 2019 and that this is due to the strengthening of the winter planetary wave activity. We find that the frequency of displacement and split SSW events differs between early, middle and late winter. Early and middle winter are dominated by displacement and split SSW events, respectively, but the frequency of the two types of event is almost equal in late winter. This is due to the differences in the relative strength of wavenumber-1 and wavenumnber-2 planetary wave activity in the three winter periods. As a result of the increase in upward planetary wave activity and the decrease in westerly winds around the polar vortex in middle winter, a shift in the timing of SSW events toward middle winter is detected. In addition, we revealed the influence of the downward propagation of different types of SSW event on the surface temperature anomaly. There were surface cold centers in Russia and northern China after the middle split SSW events; by contrast, there were more cold events in North America after the middle split SSW events.

The ozone hole measurements at the Indian station Maitri in Antarctica

Stratospheric ozone is a trace gas of great importance as it filters harmful ultraviolet radiations reaching the earth surface. Since ozone influences temperature and dynamics of the stratosphere, it is also a climate-relevant gas by modifyimg the tropospheric temperature. Significant changes in the stratospheric ozone are, therefore, a concern for human health and climate. India has a dedicated polar research programme with two stations in Antarctica; Maitri (70.4° S, 11.4° E, since 1989) and Bharati (69.2° S, 76.2° E, since 2012). Semi-regular measurements of total column ozone (TCO) are carried out to monitor the changes in the ozone layer there. Here, we use the available TCO measurements from Maitri in the winters of 1999–2003 and 2006, to estimate the chemical ozone depletion for the first time there. We estimate the largest ozone loss (59% or 180 DU) in 2006, and smallest in 2002 and 1999 (44% or 160 DU) among the winters; consistent with the meteorology, as the winter 2006 was the coldest and 2002 was the warmest with the first-ever major sudden stratospheric warming over Antarctica. The Maitri ozone loss analysis is found to be representative for the whole Antarctica as assessed from the comparisons with the average TCO from all Antarctic stations and satellite overpass TCO observations. The study, henceforth, demonstrates the value and significance of continuous monitoring of the ozone hole at Maitri to assist the policy decisions such as the Montreal Protocol and its amendments and adjustments.

Observation of the Ionosphere in Middle Latitudes during 2009, 2018 and 2018/2019 Sudden Stratospheric Warming Events

The ionospheric weather is affected not only from above by the Sun but also from below by processes in the lower-lying atmospheric layers. One of the most pronounced atmospheric phenomena is the sudden stratospheric warming (SSW). Three major SSW events from the periods of very low solar activity during January 2009, February 2018, and December 2018/January 2019 were studied to evaluate this effect of the neutral atmosphere on the thermosphere and the ionosphere. The main question is to what extent the ionosphere responds to the SSW events with focus on middle latitudes over Europe. The source of the ionospheric data was ground-based measurements by Digisondes, and the total electron content (TEC). In all three events, the ionospheric response was demonstrated as an increase in electron density around the peak height of the F2 region, in TEC, and presence of wave activity. We presume that neutral atmosphere forcing and geomagnetic activity contributed differently in individual events. The ionospheric response during SSW 2009 was predominantly influenced by the neutral lower atmosphere. The ionospheric changes observed during 2018 and 2018/2019 SSWs are a combination of both geomagnetic and SSW forcing. The ionospheric response to geomagnetic forcing was noticeably lower during time intervals outside of SSWs.

The Latitudinal Variation and Hemispheric Asymmetry of the Ionospheric Lunitidal Signatures in the American Sector During Major Sudden Stratospheric Warming Events

AbstractDuring sudden stratospheric warming events, the ionosphere exhibits phase‐shifted semidiurnal perturbations, which are typically attributed to vertical coupling associated with the semidiurnal lunar tide (M2). Our understanding of ionospheric responses to M2 is limited. This study focuses on fundamental vertical coupling processes associated with the latitudinal extent and hemispheric asymmetry of ionospheric M2 signatures using total electron content data from the American sector. Our results illustrate that the asymmetry maximizes at 15°N and 20°S magnetic latitudes. In the Southern Hemisphere, the M2‐like signatures extend deep into midlatitude and encounter the Weddell Sea Anomaly. The time evolution of the Anomaly exhibits a distortion, which is attributed to an M2 modulation. The hemispheric asymmetry of M2 signatures in the low latitude can be primarily explained by the transequatorial wind modulation of the equatorial plasma fountain. Other physical processes could also be relevant, including hemispheric asymmetry of the M2 below the F‐region, the ambient thermospheric composition and ionospheric plasma distribution, and the geomagnetic field configuration.

The January 2021 sudden stratospheric warming

On 5 January 2021, the Arctic stratospheric polar vortex dramatically weakened, and the temperature of the Arctic stratosphere rapidly increased in an event known as a major sudden stratospheric warming (SSW). It is likely that this SSW influenced surface weather conditions for over a month afterward.

Disturbance of the Stratosphere over Tomsk prior to the 2018 Major Sudden Stratospheric Warming: Effect of ClO Dimer Cycle

Disturbance of the Stratosphere over Tomsk prior to the 2018 Major Sudden Stratospheric Warming: Effect of ClO Dimer Cycle

Impact of the major SSWs of February 2018 and January 2019 on the middle atmospheric nitric oxide abundance

The Arctic middle atmosphere was affected by major sudden stratospheric warmings (SSW) in February 2018 and January 2019, respectively. In this article, we report for the first time the impact of these two events on the middle atmospheric nitric oxide (NO) abundance. The study is based on measurements obtained during two dedicated observation campaigns, using the Sub-Millimetre Radiometer (SMR) aboard the Odin satellite, measuring NO globally since 2003. The SSW of February 2018 was similar to other, more dynamically quiet, Arctic winters in term of NO downward transport from the upper mesosphere–lower thermosphere to lower altitudes (referred to as energetic particle precipitation indirect effect EPP-IE). On the contrary, the event of January 2019 led to one of the strongest EPP-IE cases observed within the Odin operational period. Important positive NO anomalies were indeed observed in the lower mesosphere–upper stratosphere during the three months following the SSW onset, corresponding to NO volume mixing ratios more than 50 times higher than the climatological values. These different consequences on the middle atmospheric composition are explained by very different dynamical characteristics of these two SSW events.

Planetary Wave Spectrum in the Stratosphere–Mesosphere during Sudden Stratospheric Warming 2018

The planetary wave activity in the stratosphere–mesosphere during the Arctic major Sudden Stratospheric Warming (SSW) in February 2018 is discussed on the basis of microwave radiometer (MWR) measurements of carbon monoxide (CO) above Kharkiv, Ukraine (50.0° N, 36.3° E) and the Aura Microwave Limb Sounder (MLS) measurements of CO, temperature and geopotential heights. From the MLS data, eastward and westward migrations of wave 1/wave 2 spectral components were differentiated, to which less attention was paid in previous studies. Abrupt changes in zonal wave spectra occurred with the zonal wind reversal near 10 February 2018. Eastward wave 1 and wave 2 were observed before the SSW onset and disappeared during the SSW event, when westward wave 1 became dominant. Wavelet power spectra of mesospheric CO variations showed statistically significant periods of 20–30 days using both MWR and MLS data. Although westward wave 1 in the mesosphere dominated with the onset of the SSW 2018, it developed independently of stratospheric dynamics. Since the propagation of upward planetary waves was limited in the easterly zonal flow in the stratosphere during SSW, forced planetary waves in the mid-latitude mesosphere may exist due to the instability of the zonal flow.

Stratospheric influence on the mesosphere–lower thermosphere over mid latitudes in winter observed by a Fabry–Perot interferometer

Abstract. In this paper, we study the response of the mesosphere–lower thermosphere (MLT) to sudden stratospheric warmings (SSWs) and the activity of planetary waves (PWs). We observe the 557.7 nm optical emission to retrieve the MLT wind and temperature with the only Fabry–Perot interferometer (FPI) in Russia. The FPI is located at the mid latitudes of eastern Siberia within the Tory Observatory (TOR) at the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS, 51.8∘ N, 103.1∘ E). Regular interferometer monitoring started in December 2016. Here, we address the temporal variations in the 557.7 nm emission intensity as well as the variations in wind and temperature measured during the 2016–2020 winters. Both SSWs and PWs appear to have equally strong effects in the upper atmosphere. When the 557.7 nm emission decreases due to some influences from below (SSWs or PWs), the temperature increases significantly, as does its variability. The dispersion of zonal wind does not show significant PW- and SSW-correlated variations, but the dominant MLT zonal wind reverses during major SSW events simultaneously with the averaged zonal wind at 60∘ N in the stratosphere.

Climatological Westward‐Propagating Semidiurnal Tides and Their Composite Response to Sudden Stratospheric Warmings in SuperDARN and SD‐WACCM‐X

AbstractUsing the Super Dual Auroral Radar Network observations (clustered around 60°N) and NCAR CESM2.0 extended Whole Atmosphere Community Climate Model nudged with reanalyzes, we examine the climatology of semidiurnal tides in meridional wind associated with the migrating component (SW2) and non‐migrating components of wavenumbers 1 (SW1) and 3 (SW3). We then illustrate their composite response to major sudden stratospheric warmings (SSWs). Peaking in late summer and winter, the climatological SW2 amplitude exceeds SW1 and SW3 except around late Fall and Spring. The winter climatological peak is absent in the model perhaps due to the zonal wind bias at the observed altitudes. The observed SW2 amplitude declines after SSW onset before enhancing ∼10 days later, along with SW1 and SW3. Within the observed region, the simulated SW2 only amplifies after SSW onset, with minimal SW1 and SW3 responses. The model reveals a stronger SW2 response above the observed location, with diminished amplitude before and enhancement after SSW globally. This enhancement appears related to increased equatorial ozone heating and background wind symmetry. The strongest SW1 and SW3 growth occurs in the Southern Hemisphere before SSW. SW2 and quasi‐stationary planetary wave activities are temporally collocated during SSW suggesting that their interactions excite SW1 and SW3. After SSW, the model also reveals (1) semidiurnal‐tide‐like perturbations generated possibly by the interactions between SW2 and westward‐traveling disturbances and (2) the enhancement of migrating semidiurnal lunar tide in the Northern Hemisphere that exceeds non‐migrating tidal and semidiurnal‐tide‐like responses. The simulated eastward‐propagating semidiurnal tides are briefly examined.

Evolution of observed ozone, trace gases, and meteorological variables over Arrival Heights, Antarctica (77.8°S, 166.7°E) during the 2019 Antarctic stratospheric sudden warming

We use ground-based spectroscopic remote sensing measurements of the stratospheric trace gases O3, HCl, ClO, BrO, HNO3, NO2, OClO, ClONO2, N2O and HF, along with radiosonde profiles of temperature to track the springtime development of the 2019 ozone hole over Arrival Heights (77.8°S, 166.7°E, AHTS), Antarctica, during, and after, the 2019 stratospheric sudden warming (SSW) event. Both measurements and model simulations show that the 2019 SSW caused an extraordinarily warm stratosphere within the polar vortex, resulting in record low ozone depletion over AHTS. We also contrast the evolution of the 2019 ozone hole to that in 2002, which also had a major springtime SSW event. The SSW event started around 28th August. By ∼17th September, stratospheric temperatures inside the polar vortex over AHTS were ∼45 K higher than the climatological average. The SSW did not cause an en masse displacement of mid-latitude air over AHTS as in the 2002 SSW event. However, the increased temperatures did cause an unusually early reduction in polar stratospheric clouds, halting the denitrification early and leading to increased gas-phase HNO3 and record high levels of NO2 (‘renoxification’). This caused the earliest observed deactivation of chlorine, returning all active chlorine into the chlorine reservoir species, HCl and ClONO2. The deactivation rate into HCl remained relatively unaffected by the SSW, whilst there was a dramatic increase in ClONO2 formation. This chlorine deactivation pathway via ClONO2 is typical of the Arctic and atypical for the Antarctic. At AHTS, record high levels of springtime ozone were observed. The measured ozone total column did not drop below 220 DU. Record high stratospheric temperatures persisted until 7th October over AHTS. By 22nd October, AHTS was not beneath the polar vortex. The polar vortex break-up date on 9th November was one of the earliest observed.

Comparison of Major Sudden Stratospheric Warming Impacts on the Mid-Latitude Mesosphere Based on Local Microwave Radiometer CO Observations in 2018 and 2019

In this paper, a comparison of the impact of major sudden stratospheric warmings (SSWs) in the Arctic in February 2018 (SSW1) and January 2019 (SSW2) on the mid-latitude mesosphere is given. The mesospheric carbon monoxide (CO) and zonal wind in these two major SSW events were observed at altitudes of 70–85 km using a microwave radiometer (MWR) at Kharkiv, Ukraine (50.0°N, 36.3°E). Data from ERA-Interim and MERRA-2 reanalyses and Aura Microwave Limb Sounder measurements were also used. It is shown that: (i) The differences between SSW1 and SSW2, in terms of local variability in zonal wind, temperature, and CO in the stratosphere and mesosphere, were clearly defined by the polar vortex (westerly in cyclonic circulation) and mid-latitude anticyclone (easterly) migrating over the MWR station, therefore; (ii) mesospheric intrusions of CO-rich air into the stratosphere over the Kharkiv region occurred only occasionally, (iii) the larger zonal wave 1–3 amplitudes before SSW1 were followed by weaker polar vortex recovery than that after SSW2, (iv) the strong vortex recovery after SSW2 was supported by earlier event timing (midwinter) favoring vortex cooling due to low solar irradiance and enhanced zonal circulation, and (v) vortex strengthening after SSW2 was accompanied by wave 1–3 amplification in March 2019, which was absent after SSW1. Finally, the influence of the large-scale circulation structures formed in individual major SSW events on the locally recorded characteristics of the atmosphere is discussed.

Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.

Multi-instrument study of the mesosphere-lower thermosphere dynamics at 80°N during the major SSW in January 2019

Contemporaneous multi-instrument ground-based optical and meteor radar observations of OH and O2 airglow, temperature and neutral winds during the winter season of November 2018–February 2019 have been used to investigate the dynamics of the mesosphere/lower thermosphere (MLT) (80–100 km) region in the high Arctic at Svalbard, Norway (78°N, 16°E) and at Eureka, Canada (80°N, 274°E). Temperature observations by the MLS Aura satellite over the 20–90 km height range for the same period were also considered. The period is characterized by an unusual major sudden stratospheric warming (SSW) event that began with a displacement of the polar vortex around December 13, 2018 (DoY 347), followed by the vortex split on January 2, 2019 (DoY 367). The MLS Aura temperature observations outlined four periods of interest: 1) late November – early December (DoY 328–335) with cold temperature anomalies in the mesosphere and warm bursts at the stratopause; 2) December 13, 2018–January 2, 2019 (DoY 347–367) when the stratopause rapidly descended to 45 km and broke down, triggering the onset of a SSW; 3) January 3–20, 2019 (DoY 368–385) during the stratopause recovery phase, and 4) from January 21, 2019 (DoY 386) onward, with the formation of the elevated stratopause and gradual return to its pre-SSW height. Both airglow emissions, OH and O2 Atm, showed simultaneously significant depletion of the integrated emission rates (IER) and temperature decrease of the order of 50–60 K, indicating upwelling, depletion of the atomic oxygen and adiabatic cooling. These cold temperature anomalies were followed by enhancements in the observed airglow IERs on December 13, 2018 (DoY 347) and January 2, 2019 (DoY 367) accompanied by a decrease in the peak altitude of the OH layer suggesting down-welling and influx of atomic oxygen from the lower thermosphere. The observations revealed oscillations with periods of 4.5–7 days, 8–10 days, and 16–21 days consistent with previously reported planetary wave activity in the winter MLT region and during major stratospheric warming events. However, the results presented here show for the first time comparisons of the multi-instrument temperature observations at 78°N – 80°N, providing an indispensable tool in monitoring the dynamics over the polar cap in general, and in describing the regional dynamical response of the MLT region to major large-scale phenomena like stratospheric warmings, in particular.

Small-scale variability of stratospheric ozone during the sudden stratospheric warming 2018/2019 observed at Ny-Ålesund, Svalbard

Abstract. Middle atmospheric ozone, water vapour and zonal and meridional wind profiles have been measured with the two ground-based microwave radiometers GROMOS-C and MIAWARA-C. The instruments have been located at the Arctic research base AWIPEV at Ny-Ålesund, Svalbard (79∘ N, 12∘ E), since September 2015. GROMOS-C measures ozone spectra in the four cardinal directions with an elevation angle of 22∘. This means that the probed air masses at an altitude of 3 hPa (37 km) have a horizontal distance of 92 km to Ny-Ålesund. We retrieve four separate ozone profiles along the lines of sight and calculate daily mean horizontal ozone gradients which allow us to investigate the small-scale spatial variability of ozone above Ny-Ålesund. We present the evolution of the ozone gradients at Ny-Ålesund during winter 2018/2019, when a major sudden stratospheric warming (SSW) took place with the central date at 2 January, and link it to the planetary wave activity. We further analyse the SSW and discuss our ozone and water vapour measurements in a global context. At 3 hPa we find a distinct seasonal variation of the ozone gradients. The strong polar vortex during October and March results in a decreasing ozone volume mixing ratio towards the pole. In November the amplitudes of the planetary waves grow until they break in the end of December and an SSW takes place. From November until February ozone increases towards higher latitudes and the magnitude of the ozone gradients is smaller than in October and March. We attribute this to the planetary wave activity of wave numbers 1 and 2 which enabled meridional transport. The MERRA-2 reanalysis and the SD-WACCM model are able to capture the small-scale ozone variability and its seasonal changes.

Predictability of European Winters 2017/2018 and 2018/2019: Contrasting influences from the Tropics and stratosphere

AbstractThe European winters of 2017–18 and 2018–19 were not climatically extreme, but both winters had a major sudden stratospheric warming (SSW). In February 2018, an SSW led to an intense cold outbreak across Europe and further spells of cold weather in March. The SSW of January 2019, although well predicted and expected to increase the chance of a cold end to winter, apparently produced little impact. In this study, we examine the performance of the Met Office seasonal prediction system in these winters, and the influences that led to these outcomes. To achieve this latter objective, sets of numerical experiments are performed in which the tropical troposphere and the extratropical stratosphere are relaxed towards their observed state, allowing the influence of each on the North Atlantic‐European atmospheric circulation to be identified. Using these experiments, we show that the SSWs had similar impacts in each case, creating a signal of easterly surface wind anomalies in the weeks following the event. In contrast, tropical influences were opposite in the two winters, acting to strengthen the easterly signal at the end of February 2018 and opposing it in January 2019. The different apparent responses to the two events therefore came about largely through tropical tropospheric variability. Furthermore, we highlight the importance of a very strong cycle of the Madden‐Julian Oscillation (MJO) in late January and early February 2018 as an important driver for the February 2018 SSW. MJO teleconnections appear to have been critical in creating the large mid‐latitude wave 2 amplitude that has been identified as the immediate cause of this event.