Stratospheric Polar Vortex Research Articles

Influence of Major Stratospheric Sudden Warming on the Unprecedented Cold Wave in East Asia in January 2021

An unprecedented cold wave intruded into East Asia in early January 2021 and led to record-breaking or historical extreme low temperatures over vast regions. This study shows that a major stratospheric sudden warming (SSW) event at the beginning of January 2021 exerted an important influence on this cold wave. The major SSW event occurred on 2 January 2021 and subsequently led to the displacement of the stratospheric polar vortex to the East Asian side. Moreover, the SSW event induced the stratospheric warming signal to propagate downward to the mid-to-lower troposphere, which not only enhanced the blocking in the Urals–Siberia region and the negative phase of the Arctic Oscillation, but also shifted the tropospheric polar vortex off the pole. The displaced tropospheric polar vortex, Ural blocking, and another downstream blocking ridge over western North America formed a distinct inverted omega-shaped circulation pattern (IOCP) in the East Asia–North Pacific sector. This IOCP was the most direct and impactful atmospheric pattern causing the cold wave in East Asia. The IOCP triggered a meridional cell with an upward branch in East Asia and a downward branch in Siberia. The meridional cell intensified the Siberian high and low-level northerly winds, which also favored the invasion of the cold wave into East Asia. Hence, the SSW event and tropospheric circulations such as the IOCP, negative phase of Arctic Oscillation, Ural blocking, enhanced Siberian high, and eastward propagation of Rossby wave eventually induced the outbreak of an unprecedented cold wave in East Asia in early January 2021.

Potential Links Between Tropospheric and Stratospheric Circulation Extremes During Early 2020

AbstractFebruary‐March 2020 was marked by highly anomalous large‐scale circulations in the Northern extratropical troposphere and stratosphere. The Atlantic jet reached extreme strength, linked to some of the strongest and most persistent positive values of the Arctic Oscillation index on record, which provided conditions for extreme windstorms hitting Europe. Likewise, the stratospheric polar vortex reached extreme strength that persisted for an unusually long period. Past research indicated that such circulation extremes occurring throughout the troposphere‐stratosphere system are dynamically coupled, although the nature of this coupling is still not fully understood and generally difficult to quantify. We employ sets of numerical ensemble simulations to statistically characterize the mutual coupling of the early 2020 extremes. We find the extreme vortex strength to be linked to the reflection of upward propagating planetary waves and the occurrence of this reflection to be sensitive to the details of the vortex structure. Our results show an overall robust coupling between tropospheric and stratospheric anomalies: ensemble members with polar vortex exceeding a certain strength tend to exhibit a stronger tropospheric jet and vice versa. Moreover, members exhibiting a breakdown of the stratospheric circulation (e.g., sudden stratospheric warming) tend to lack periods of persistently enhanced tropospheric circulation. Despite indications for vertical coupling, our simulations underline the role of internal variability within each atmospheric layer. The circulation extremes during early 2020 may be viewed as resulting from a fortuitous alignment of dynamical evolutions within the troposphere and stratosphere, aided by each layer's modification of the other layer's boundary condition.

Impacts of Sudden Stratospheric Warming on Extreme Cold Events in Early 2021: An Ensemble‐Based Sensitivity Analysis

AbstractImpacts of sudden stratospheric warming (SSW) on three severe cold events (C1–C3) over Northern Hemisphere in early 2021 were investigated using subseasonal‐to‐seasonal ensemble forecasts. The SSW was characterized by successive displacement and split of the stratospheric polar vortex (SPV). Ensemble‐based sensitivity analyses showed that C1 over Siberia and C2 over western Canada were more related to SPV variations at a lead time of 1–2 weeks than C3 over central U.S. Within ensemble forecasts, a more elongated SPV with higher geopotential height over northern Eurasia were conducive to C1, whereas a SPV with the more poleward retreat from displacement contributed to C2. The forecast accuracy of stratospheric heights over the sensitive region at 2 weeks lead was significantly correlated with the forecast skill of the tropospheric circulation pattern preceding C1, implying that prediction of specific cold weather events may be improved by a better forecast of key features in SPV variations.

Impacts of stratospheric polar vortex changes on wintertime precipitation over the northern hemisphere

Impacts of stratospheric polar vortex changes on wintertime precipitation over the northern hemisphere

Possible impact of sudden stratospheric warming on the intraseasonal reversal of the temperature over East Asia in winter 2020/21

The intraseasonal reversal of the temperature over East Asia and the sudden stratospheric warming (SSW) are two abrupt events during the winter of 2020/21. The characteristics of these two events and their relationship are the focused issues in this paper. In winter 2020/21, there was a transition from cold to warm over East Asia. The surface air temperature (SAT) in East Asia suddenly changed from cold to warm with long duration. The cold period lasted from 21 November 2020 to 11 January 2021, while the warm period lasted from 19 January to 28 February 2021. And the transition of the cold to the warm was from 12 to 18 January 2021.There were significant differences of the atmospheric circulations between the cold and warm periods in the upper and lower troposphere. During the cold period, both of Ural Mountain High(UH) and Siberian High(SH) were stronger than normal, the Westerly Jet (WJ) was weakened and located to the area farther southerly than usual, the northerly wind anomalies and the cold advection occurred in East Asian; vice versa during the warm period. The mutations of the atmospheric circulations in the upper and lower levels were obvious during the transition period, especially for UH and SH. A strong SSW event occurred in the stratosphere at the beginning of 2021. As a result, the stratospheric polar vortex was largely weakened and deviated to the areas over Ural Mountains and nearby, the polar westerly wind turned to easterly wind and the temperature gradient reversed. The abnormal changes of the temperature and the geopotential height over the Ural Mountains area in the stratosphere were closely related to the SSW. These abnormal signals caused by the SSW gradually transmitted from stratosphere to troposphere over the Ural Mountains and the polar region, leading to the weakening and collapse of tropospheric UH and further caused the transition from cold to warm in East Asia. The SSW may be the most critical factor leading to the turning from cold to warm over East Asia during the winter of 2020/21.

Modeling stratospheric polar vortex variation and identifying vortex extremes using explainable machine learning

Abstract The winter stratospheric polar vortex (SPV) exhibits considerable variability in magnitude and structure, which can result in extreme SPV events. These extremes can subsequently influence weather in the troposphere from weeks to months and thus are important sources of surface predictability. However, the predictability of the SPV extreme events is limited to 1–2 weeks in state-of-the-art prediction systems. Longer predictability timescales of SPV would strongly benefit long-range surface prediction. One potential option for extending predictability timescales is the use of machine learning (ML). However, it is often unclear which predictors and patterns are important for ML models to make a successful prediction. Here we use explainable multiple linear regressions (MLRs) and an explainable artificial neural network (ANN) framework to model SPV variations and identify one type of extreme SPV events called sudden stratospheric warmings. We employ a NN attribution method to propagate the ANN’s decision-making process backward and uncover feature importance in the predictors. The feature importance of the input is consistent with the known precursors for extreme SPV events. This consistency provides confidence that ANNs can extract reliable and physically meaningful indicators for the prediction of the SPV. In addition, our study shows a simple MLR model can predict the SPV daily variations using sequential feature selection, which provides hints for the connections between the input features and the SPV variations. Our results indicate the potential of explainable ML techniques in predicting stratospheric variability and extreme events, and in searching for potential precursors for these events on extended-range timescales.

Antarctic planetary wave spectrum under different polar vortex conditions in 2019 and 2020 based on total ozone column data

We examine the zonal wavenumber spectrum of planetary (Rossby) waves in the atmosphere above Antarctica in each of two contrasting years: in 2019, when there was a sudden stratospheric warming (SSW), and in 2020 when the Antarctic stratospheric vortex was unusually strong and long-lived. The ozone hole (OH) is developed over Antarctica in spring, and its state depends on disturbances of the stratospheric polar vortex by planetary waves (PW). Our analysis uses data on the distribution of the total ozone column from the Ozone Monitoring Instrument on the Aura satellite and ground-based measurements from the Dobson spectrophotometer at the Ukrainian Antarctic Akademik Vernadsky station in Antarctica. The 2019 SSW strongly displaced the Antarctic vortex off-pole and aided the breakdown of the ozone hole. The SSW occurred during the peak activity of quasi-stationary planetary wave-1, which was enhanced at the time of the warming by the large amplitude of traveling wave-2. In the spring of 2020, the stratospheric polar vortex was relatively undisturbed, allowing the OH area to attain a size close to its historical maximum. A factor in 2020 that aided the stability of the vortex was the relatively small amplitude of wave-1. The stability was maintained despite regular periods when the amplitude of traveling wave-2 attained or even exceeded values around the time of the SSW in 2019. We find that a factor contributing to the differences between the wave effects in the two years is the dynamics of the quasi-stationary wave-1. Anticorrelation of the wave-1 and wave-2 amplitudes near the edge of the vortex was clearly observed in 2020, which can be caused by the transfer of planetary wave energy between different spectral wave components, unlike the situation in 2019.

成層圏極渦の再検討：渦崩壊の新しい診断法

成層圏極渦の再検討：渦崩壊の新しい診断法

The Antarctic ozone hole during 2020

The Antarctic ozone hole remains the focus of scientific attention because of its importance to the health of the biosphere and its influence on the climate of the southern hemisphere. Here we examine the general characteristics of the 2020 Antarctic ozone hole using a variety of observational and reanalysis data and compare and contrast its behaviour with earlier years. The main feature of the 2020 ozone hole was its relatively large size, and persistence to the beginning of the 2020/2021 summer, with new maximum records being set for the ozone hole daily area and ozone mass deficit during November and December. This was in strong contrast to 2019 when the ozone hole was one of the smallest observed. We show that a key factor in 2020 was the relative stability and strength of the stratospheric polar vortex, which allowed low temperatures in the Antarctic lower stratosphere to enhance ozone depletion reactions in relative isolation from the rest of the global atmosphere. These conditions were associated with relatively weak Rossby wave activity at high southern latitudes that occurred during the strengthening westerly phase of the Quasi Biennial Oscillation as well as the emerging La Niña phase of the El Niño Southern Oscillation. A consequence of the conditions in early summer was the measurement of new maximum values of ultraviolet radiation at Australia’s three Antarctic research stations of Mawson, Davis and Casey. Indications of anomalous chlorine partitioning above Arrival Heights in Antarctica prior to the 2020 winter are provided, which may relate to effects from the 2019/2020 Australian wildfires. We also examine the effect of the downward coupling of the 2020 ozone hole to the climate of the wider southern hemisphere, which showed regional influences on surface temperature and precipitation in common with other strong vortex years.

On the Existence of the Predictability Barrier in the Wintertime Stratospheric Polar Vortex: Intercomparison of Two Stratospheric Sudden Warmings in 2009 and 2010 Winters

On the Existence of the Predictability Barrier in the Wintertime Stratospheric Polar Vortex: Intercomparison of Two Stratospheric Sudden Warmings in 2009 and 2010 Winters

Features of the stratospheric polar vortex weakening prior to breakdown

Features of the stratospheric polar vortex weakening prior to breakdown

Reversal of monthly East Asian winter air temperature in 2020/21 and its predictability

In this study, the reversal of monthly East Asian winter air temperature (EAWT) in 2020/21 and its predictability were investigated. The reversal of monthly EAWT in 2020/21 was characterized by colder temperatures in early winter (December 2020 to mid-January 2021) and warmer temperatures in late winter (mid-January to February 2021). Results show that the reversal in the intensity of the Siberian high (SH) also occurred between early and late winter in 2020/21. In early winter, as the Barents–Laptev sea ice in the previous September (i.e., in 2020) reached a minimum for the period 1981–2020, the SH was strengthened via a reduction of the meridional gradient between the Arctic and East Asia. In late winter, as a sudden stratospheric warming occurred on 5 January 2021, the stratospheric polar vortex weakened, with the weakest center shifting to North America in January. Subsequently, the negative Arctic Oscillation–like structure shifted towards North America in the middle and lower troposphere, which weakened the SH in late winter. Furthermore, the predictability of the reversal in EAWT in 2020/21 was validated based on monthly and daily predictions from NCEP-CFSv2 (National Centers for Environment Prediction–Climate Forecast System, version 2). The results showed that the model was unable to reproduce the monthly reversal of EAWT. However, it was able to forecast the reversal date (18 January 2021) of EAWT at lead times of 1–20 days on the daily scale.摘要在全球变暖的背景下, 近年来东亚冬季气温存在复杂的季节内变化. 本文研究了2020/21年东亚冬季气温的月际转折及可预测性. 结果表明, 2020/21年东亚冬季气温前冬 (2020年12月–2021年1月中旬) 偏冷, 后冬 (2021年1月中旬–2月) 偏暖. 西伯利亚高压强度在前冬和后冬也出现转折变化. 在前冬, 由于2020年9月巴伦支海–拉普捷夫海海冰达到1981–2020年以来的最小值, 北极至东亚地区的温度梯度减弱, 西伯利亚高压增强. 在后冬, 由于2021年1月5日发生平流层爆发性增温, 1月平流层极涡减弱增暖, 且最弱中心向北美偏移. 因此, 对流层中低层负的类北极涛动位相也向北美偏移, 西伯利亚高压减弱.基于NCEP-CFSv2月际和逐日的预测结果显示, 该预测系统不能较好地再现此次东亚冬季气温的月际转折. 然而, 在日尺度上, 模式能提前1–20天较好地预测东亚冬季气温的转折日期.

Arctic Stratosphere Circulation Changes in the 21st Century in Simulations of INM CM5

Simulations of Institute of Numerical Mathematics (INM) coupled climate model 5th version for the period from 2015 to 2100 under moderate (SSP2-4.5) and severe (SSP5-8.5) scenarios of greenhouse gases growth are analyzed to investigate changes of Arctic polar stratospheric vortex, planetary wave propagation, Sudden Stratospheric Warming frequency, Final Warming dates, and meridional circulation. Strengthening of wave activity propagation and a stationary planetary wave number 1 in the middle and upper stratosphere, acceleration of meridional circulation, an increase of winter mean polar stratospheric volume (Vpsc) and strengthening of Arctic stratosphere interannual variability after the middle of 21st century, especially under a severe scenario, were revealed. March monthly values of Vpsc in some winters could be about two times more than observed ones in the Arctic stratosphere in the spring of 2011 and 2020, which in turn could lead to large ozone layer destruction. Composite analysis shows that “warm” winters with the least winter mean Vpsc values are characterized by strengthening of wave activity propagation from the troposphere into the stratosphere in December but weaker propagation in January–February in comparison with winters having the largest Vpsc values.

A Minimal Model to Diagnose the Contribution of the Stratosphere to Tropospheric Forecast Skill

AbstractMany recent studies have confirmed that variability in the stratosphere is a significant source of surface sub‐seasonal prediction skill during Northern Hemisphere winter. It may be beneficial, therefore, to think about times in which there might be windows‐of‐opportunity for skillful sub‐seasonal predictions based on the initial or predicted state of the stratosphere. In this study, we propose a simple, minimal model that can be used to understand the impact of the stratosphere on tropospheric predictability. Our model purposefully excludes state dependent predictability in either the stratosphere or troposphere or in the coupling between the two. Model parameters are set up to broadly represent current sub‐seasonal prediction systems by comparison with four dynamical models from the Sub‐Seasonal to Seasonal Prediction Project database. The model can reproduce the increases in correlation skill in sub‐sets of forecasts for weak and strong lower stratospheric polar vortex states over neutral states despite the lack of dependence of coupling or predictability on the stratospheric state. We demonstrate why different forecast skill diagnostics can give a very different impression of the relative skill in the three sub‐sets. Forecasts with large stratospheric signals and low amounts of noise are demonstrated to also be windows‐of‐opportunity for skillful tropospheric forecasts, but we show that these windows can be obscured by the presence of unrelated tropospheric signals.

Dynamical and surface impacts of the January 2021 sudden stratospheric warming in novel Aeolus wind observations, MLS and ERA5

Abstract. Major sudden stratospheric warmings (SSWs) are extreme dynamical events where the usual strong westerly winds of the stratospheric polar vortex temporarily weaken or reverse and polar stratospheric temperatures rise by tens of kelvins over just a few days and remain so for an extended period. Via dynamical modification of the atmosphere below them, SSWs are believed to be a key contributor to extreme winter weather events at the surface over the following weeks. SSW-induced changes to the wind structure of the polar vortex have previously been studied in models and reanalyses and in localised measurements such as radiosondes and radars but have not previously been directly and systematically observed on a global scale because of the major technical challenges involved in observing winds from space. Here, we exploit novel observations from ESA's flagship Aeolus wind-profiler mission, together with temperature and geopotential height data from NASA's Microwave Limb Sounder and surface variables from the ERA5 reanalysis, to study the 2021 SSW. This allows us to directly examine wind and related dynamical changes associated with the January 2021 major SSW. Aeolus is the first satellite mission to systematically and directly acquire profiles of wind, and therefore our results represent the first direct measurements of SSW-induced wind changes at the global scale. We see a complete reversal of the zonal winds in the lower to middle stratosphere, with reversed winds in some geographic regions reaching down to the bottom 2 km of the atmosphere. These altered winds are associated with major changes to surface temperature patterns, and in particular we see a strong potential linkage from the SSW to extreme winter weather outbreaks in Greece and Texas during late January and early February. Our results (1) demonstrate the benefits of wind-profiling satellites such as Aeolus in terms of both their direct measurement capability and use in supporting reanalysis-driven interpretation of stratosphere–troposphere coupling signatures, (2) provide a detailed dynamical description of a major weather event, and (3) have implications for the development of Earth-system models capable of accurately forecasting extreme winter weather.

Contrasting Effects of Indian Ocean Basin and Dipole Modes on the Stratosphere

AbstractThe stratospheric impact of the sea surface temperature (SST) variability in the Indian Ocean has attracted extensive attention. Recent warming of the tropical Indian Ocean is characterized by increases in both the magnitude and zonal gradient, which is related to the variability in the positive phase of the Indian Ocean basin mode (IOBM) and Indian Ocean dipole mode (IOD). Yet, previous studies mainly focused on the stratospheric impact of the IOBM. Using the Whole Atmosphere Community Climate Model (version 4), this study explores the impact of positive IOD events on the stratosphere and compares it with the IOBM. Results show that the IOBM (IOD) serves to dry (moisten) the tropical lower stratosphere on the annual average. The moistening (drying) of the lower stratosphere in response to IOBM occurs mainly in winter and spring (autumn), while the IOD exerts a moistening effect in winter. Both modes can enhance the northern stratospheric polar vortex, and the effect of IOD is close to that of IOBM, although SST anomalies associated with the IOD are smaller. This implies that the Indian Ocean SST gradient exerts a greater influence on the Northern Hemisphere stratosphere than does the Indian Ocean SST magnitude. Moreover, both modes weaken the southern stratospheric polar vortex, but the effect of IOD is much smaller since its impact on stationary waves is weak. Contrary to the Northern Hemisphere stratosphere, the Southern Hemisphere stratosphere is more sensitive to the Indian Ocean SST magnitude than to the SST gradient.

Intensified Impact of Winter Arctic Oscillation on Simultaneous Precipitation Over the Mid–High Latitudes of Asia Since the Early 2000s

This study reveals an intensified impact of winter (November–February mean) Arctic Oscillation (AO) on simultaneous precipitation over the mid–high latitudes of Asia (MHA) since the early 2000s. The unstable relationship may be related to the changes in the tropospheric AO mode and the subtropical jet. Further analyses suggest that their changes may be attributable to the interdecadal changes in the stratospheric polar vortex. During 2002–2017, the anomalously weak stratospheric polar vortex is accompanied by intensified upward-propagating tropospheric planetary-scale waves anomalies. Subsequently, the stratospheric geopotential height anomalies over the North Atlantic high-latitudes propagate downward strongly, causing the changes in the tropospheric AO mode, that is, the positive height anomalies over the North Atlantic high-latitudes are stronger and extend southward, corresponding to the stronger and eastward extension of negative height anomalies over the North Atlantic mid-latitudes. Thus, the Rossby wave source anomalies over Baffin Bay and the Black Sea are strong, and correspondingly so too are their subsequently excited the Rossby waves anomalies. Meanwhile, the planetary-scale waves anomalies propagate weakly along the low-latitude waveguide, causing the intensified and southward shift of the subtropical jet. Therefore, the strong Rossby waves anomalies propagate eastward to the MHA. By contrast, during 1979–1999, the strong stratospheric polar vortex anomaly is accompanied by weak upward-propagating planetary-scale waves anomalies, resulting in weaker height anomalies over the North Atlantic mid–high latitudes. Consequently, the anomalous Rossby waves are weak. In addition, the subtropical jet weakens and shifts northward, which causes the Rossby waves anomalies to dominate over the North Atlantic, and thereby the impact of winter AO on simultaneous precipitation over the MHA is weak.

Effects of Energetic Solar Proton Events of Solar Cycle 23 on Intensity of the Stratospheric Polar Vortex

Effects of Energetic Solar Proton Events of Solar Cycle 23 on Intensity of the Stratospheric Polar Vortex

The dominant intraseasonal variability mode of tropical convection in the 2 weeks before a Northern Hemisphere extreme stratospheric polar vortex

AbstractThe Madden–Julian Oscillation (MJO) phase 7 has been recognized as a driver for Northern Hemisphere (NH) sudden stratospheric warmings (SSWs) in the literature recently. However, uncertainties remain on the exact relationship between MJO phase 3 and the stratospheric polar vortex. Here, we re‐examined and compared the observed evolution of the MJO before the two types of NH extreme stratospheric polar vortex events (i.e. strong vortex (SV) events and weak vortex (WV) events) in this study. Our analysis reveals that MJO phase 3 (7) is the dominant intraseasonal variability mode in about 2 weeks before onset of the SV (WV) events, suggesting these two phases are closely linked to variation in the intensity of the stratospheric polar vortex. MJO phase 3 (7) leads to a strengthened (weakened) polar vortex due to the suppressed (enhanced) wave‐number 1 wave activity in the extratropical stratosphere resulting from destructive (constructive) interference between the negative (positive) Pacific–North American (PNA)‐like pattern induced by MJO phase 3 (7) and the background field. Note that the time‐scales for the peak responses of wave activity in the extratropical stratosphere to MJO phases 3 and 7 are around 2 weeks and 1 week, respectively. Thus, within 2 weeks, MJO phase 3 (7) can be treated as the precursor to the strengthened (weakened) polar vortex.

Network-based forecasting of climate phenomena

Network theory, as emerging from complex systems science, can provide critical predictive power for mitigating the global warming crisis and other societal challenges. Here we discuss the main differences of this approach to classical numerical modeling and highlight several cases where the network approach substantially improved the prediction of high-impact phenomena: 1) El Niño events, 2) droughts in the central Amazon, 3) extreme rainfall in the eastern Central Andes, 4) the Indian summer monsoon, and 5) extreme stratospheric polar vortex states that influence the occurrence of wintertime cold spells in northern Eurasia. In this perspective, we argue that network-based approaches can gainfully complement numerical modeling.