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Polar vortex : climate change and its effects
\"The events surrounding the 2014 polar vortex did not look the same to everyone involved. Readers can step back in time and into the shoes of a college student, a New Yorker, and a coal miner as readers act out scenes and compare and contrast various perspectives. Written with simplified, considerate text to help struggling readers, books in this series are made to build confidence as readers engage and read aloud. Includes a table of contents, glossary, index, author biography, sidebars, and timeline\"-- Provided by publisher.
Book
Siege in the Southern Stratosphere: Hunga Tonga‐Hunga Ha'apai Water Vapor Excluded From the 2022 Antarctic Polar Vortex
We use Aura Microwave Limb Sounder (MLS) trace gas measurements to investigate whether water vapor (H2O) injected into the stratosphere by the Hunga Tonga‐Hunga Ha'apai (HTHH) eruption affected the 2022 Antarctic stratospheric vortex. Other MLS‐measured long‐lived species are used to distinguish high HTHH H2O from that descending in the vortex from the upper‐stratospheric H2O peak. HTHH H2O reached high southern latitudes in June–July but was effectively excluded from the vortex by the strong transport barrier at its edge. MLS H2O, nitric acid, chlorine species, and ozone within the 2022 Antarctic polar vortex were near average; the vortex was large, strong, and long‐lived, but not exceptionally so. There is thus no clear evidence of HTHH influence on the 2022 Antarctic vortex or its composition. Substantial impacts on the stratospheric polar vortices are expected in succeeding years since the H2O injected by HTHH has spread globally. Plain Language Summary The 2022 Hunga Tonga‐Hunga Ha'apai eruption injected vast amounts of water vapor into the stratosphere. Concern arose that this excess water vapor could affect the 2022 Antarctic stratospheric polar vortex and ozone hole: Water vapor plays a crucial role in forming polar stratospheric clouds, which provide surfaces upon which chemical reactions that destroy ozone take place. Enhanced water vapor also affects temperatures, which in turn affect the powerful winds defining the polar vortex boundary. Antarctic polar vortex development began in April–May; by June the intense vortex‐edge winds presented a formidable obstacle to transport. Satellite trace‐gas measurements show that when water vapor from the Hunga Tonga eruption reached the vortex edge in June, it faced an impenetrable barrier and “besieged” the vortex, building up exceptionally strong water vapor gradients across the vortex edge. Water vapor, ozone, and chemicals involved in ozone destruction remained near historical average levels within the vortex through spring 2022. Because excess water vapor spread throughout the south polar regions after vortex breakup, much larger effects on the Antarctic vortex and chemical processing within it are expected in 2023 and beyond, when high water vapor will be entrained into the vortex as it develops. Key Points Microwave Limb Sounder (MLS) trace gas data show that the Hunga Tonga‐Hunga Ha'apai H2O plume was effectively excluded from the 2022 Antarctic polar vortex Antarctic lower stratospheric vortex strength, size, and longevity were among the largest on record, but within the range of previous years Antarctic chemical ozone loss in 2022 was unexceptional, with MLS ozone and related trace gases observed to be near average
Journal Article
Windows of Opportunity for Skillful Forecasts Subseasonal to Seasonal and Beyond
There is high demand and a growing expectation for predictions of environmental conditions that go beyond 0–14-day weather forecasts with outlooks extending to one or more seasons and beyond. This is driven by the needs of the energy, water management, and agriculture sectors, to name a few. There is an increasing realization that, unlike weather forecasts, prediction skill on longer time scales can leverage specific climate phenomena or conditions for a predictable signal above the weather noise. Currently, it is understood that these conditions are intermittent in time and have spatially heterogeneous impacts on skill, hence providing strategic windows of opportunity for skillful forecasts. Research points to such windows of opportunity, including El Niño or La Niña events, active periods of the Madden–Julian oscillation, disruptions of the stratospheric polar vortex, when certain large-scale atmospheric regimes are in place, or when persistent anomalies occur in the ocean or land surface. Gains could be obtained by increasingly developing prediction tools and metrics that strategically target these specific windows of opportunity. Across the globe, reevaluating forecasts in this manner could find value in forecasts previously discarded as not skillful. Users’ expectations for prediction skill could be more adequately met, as they are better aware of when and where to expect skill and if the prediction is actionable. Given that there is still untapped potential, in terms of process understanding and prediction methodologies, it is safe to expect that in the future forecast opportunities will expand. Process research and the development of innovative methodologies will aid such progress.
Journal Article
Compound Dry–Hot Conditions in South and Southeast Asia Modulated by the Arctic Stratospheric Polar Vortex
Compound dry–hot conditions increasingly threaten South and Southeast Asia, highlighting the need to understand drivers. Observations and numerical simulations reveal a robust polar–low‐latitude teleconnection: the March Arctic stratospheric polar vortex (ASPV) strongly modulates March–April compound dry–hot conditions across the region. When the March ASPV weakens, anomalous easterlies in the lower Arctic stratosphere induce corresponding tropospheric easterlies and persist through April, cooling Siberia and accelerating the mid‐latitude westerlies. The resulting anticyclonic shear drives an anomalous anticyclone over northern South and Southeast Asia. Combined with the region's climatologically dry–hot season, these processes promote compound dry–hot conditions further amplified by positive soil moisture–atmosphere feedback. Moreover, the March ASPV outweighs the preceding winter tropical sea surface temperature in shaping compound dry–hot variability in this northern sector. Our results highlight the critical role of the Arctic stratospheric anomalies in driving low‐latitude climate, helping improve risk mitigation.
Journal Article
The Cold‐Pole Bias Severely Weakens Southern Hemisphere Springtime Stratosphere‐Troposphere Coupling
A too cold and too strong Antarctic stratospheric polar vortex (ASPV) in spring (the so‐called cold‐pole bias) is a common model problem. This study investigates the impact of the cold‐pole bias on Southern Hemisphere springtime stratosphere‐troposphere coupling and how this impact is affected by interactive ozone using a pair of Goddard Earth Observing System (GEOS) simulations with and without interactive chemistry. The cold‐pole bias in the GEOS simulations delays the poleward and downward progression of the ASPV and stratosphere‐troposphere coupling in spring by 1–2 months, causing severe underestimation of stratosphere‐troposphere coupling in October–November. Consequently, the simulations poorly capture or completely miss the observed springtime tropospheric predictability from ASPV conditions in late winter/early spring. Compared to the prescribed ozone simulation, interactive ozone exacerbates the cold‐pole bias by overpredicting Antarctic ozone loss, leading to degradation of springtime stratosphere‐troposphere coupling and loss of tropospheric predictability.
Journal Article
The Sudden Stratospheric Warming Events in the Antarctic in 2024
In July and August 2024, two consecutive stratospheric sudden warming (SSW) events (termed SW07 and SW08) occurred over Antarctic, both featuring a rapid 17°C temperature rise at 10 hPa and significant stratospheric polar vortex (SPV) deceleration. SW07 occurred at the earliest winter time of the year recorded in the satellite era (1979 to present). The study found that, strong blocking highs affected stratospheric warming via nonlinear planetary wave prior to SW07, and the substantial sea ice loss over Antarctic Ross Sea and Amundsen Sea likely created favorable conditions for the formation of these blocking highs. Furthermore, the stratospheric preconditioning significantly amplified the intensity of the planetary waves. A downward‐propagating negative Southern Annular Mode (SAM) signal after SW07 supported blocking highs, creating a favorable circulation for planetary wave perturbations prior to SW08. In addition, enhanced ozone transport from low latitudes to the pole during SW07 and SW08 contributed to ozone recovery.
Journal Article
Northern winter stratospheric polar vortex regimes and their possible influence on the extratropical troposphere
The possible influence of changes in the Arctic stratospheric polar vortex on the extratropical troposphere especially in the mid-to-high latitudes of the Northern Hemisphere is still not well understood. Using the ERA5 reanalysis and based on the k-mean clustering algorithm, the northern winter stratospheric polar vortex is categorized into several regimes, which mainly reflect the difference in the intensity and central position of the vortex. As a consequence, the stratospheric polar vortex can be clustered into six groups, including the homogeneously-intensified (HI), homogeneously-weakened (HW), North America-intensified (NAI), North America-weakened (NAW), Eurasia-intensified (EUI), and Eurasia-weakened (EUW) shapes. Statistics of each polar vortex clustering confirms that the yearly frequency of the HI state shows a decreasing trend in past decades, while the HW increases as inferred from the long-term trend. Further, the evolutions of the tropospheric circulation and climate anomalies are explored following each clustering. It is revealed that both the strength and central position of the stratospheric polar vortex significantly modulate the behavior of tropospheric circulation and near surface climate. The relationship between the stratospheric polar vortex regimes and the tropospheric teleconnections are examined. The conventional stratosphere–troposphere coupling via the downward propagation of the North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) signal is confirmed. Other tropospheric teleconnections are also associated with the stratospheric regimes. The Pacific-North American pattern (PNA) is well correlated with the shift of the stratospheric polar vortex, and the Eurasian pattern (EU) is sensitive to the HI and NAW patterns. The patterns of rainfall and temperature anomalies following the six stratospheric regimes are different.
Journal Article
MORE-PERSISTENT WEAK STRATOSPHERIC POLAR VORTEX STATES LINKED TO COLD EXTREMES
The extratropical stratosphere in boreal winter is characterized by a strong circumpolar westerly jet, confining the coldest temperatures at high latitudes. The jet, referred to as the stratospheric polar vortex, is predominantly zonal and centered around the pole; however, it does exhibit large variability in wind speed and location. Previous studies showed that a weak stratospheric polar vortex can lead to cold-air outbreaks in the midlatitudes, but the exact relationships and mechanisms are unclear. Particularly, it is unclear whether stratospheric variability has contributed to the observed anomalous cooling trends in midlatitude Eurasia. Using hierarchical clustering, we show that over the last 37 years, the frequency of weak vortex states in mid- to late winter (January and February) has increased, which was accompanied by subsequent cold extremes in midlatitude Eurasia. For this region, 60% of the observed cooling in the era of Arctic amplification, that is, since 1990, can be explained by the increased frequency of weak stratospheric polar vortex states, a number that increases to almost 80% when El Niño–Southern Oscillation (ENSO) variability is included as well.
Journal Article
The 2019 Southern Hemisphere Stratospheric Polar Vortex Weakening and Its Impacts
This 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.
Journal Article
Australian hot and dry extremes induced by weakenings of the stratospheric polar vortex
The occurrence of extreme hot and dry conditions in warm seasons can have large impacts on human health, energy and water supplies, agriculture and wildfires. Australian hot and dry extremes have been known to be associated with the occurrence of El Niño and other variations of tropospheric circulation. Here we identify an additional driver: variability of the stratospheric Antarctic polar vortex. On the basis of statistical analyses using observational data covering the past 40 yr, we show that weakenings and warmings of the stratospheric polar vortex, which episodically occur during austral spring, substantially increase the chances of hot and dry extremes and of associated fire-conducive weather across subtropical eastern Australia from austral spring to early summer. The promotion of these Australian climate extremes results from the downward coupling of the weakened polar vortex to tropospheric levels, where it is linked to the low-index polarity of the Southern Annular Mode, an equatorward shift of the mid-latitude westerly jet stream and subsidence and warming in the subtropics. Because of the long timescale of the polar vortex variations, the enhanced likelihood of early-summertime hot and dry extremes and wildfire risks across eastern Australia may be predictable a season in advance during years of vortex weakenings.
Journal Article