Skillful Seasonal Prediction of the Southern Annular Mode and Antarctic Ozone

Abstract Using a set of seasonal hindcast simulations produced by the Met Office Global Seasonal Forecast System, version 5 (GloSea5), significant predictability of the southern annular mode (SAM) is demonstrated during the austral spring. The correlation of the September–November mean SAM with observed values is 0.64, which is statistically significant at the 95% confidence level [confidence interval: (0.18, 0.92)], and is similar to that found recently for the North Atlantic Oscillation in the same system. Significant skill is also found in the prediction of the strength of the Antarctic stratospheric polar vortex at 1 month average lead times. Because of the observed strong correlation between interannual variability in the strength of the Antarctic stratospheric circulation and ozone concentrations, it is possible to make skillful predictions of Antarctic column ozone amounts. By studying the variation of forecast skill with time and height, it is shown that skillful predictions of the SAM are significantly influenced by stratospheric anomalies that descend with time and are coupled with the troposphere. This effect allows skillful statistical forecasts of the October mean SAM to be produced based only on midstratosphere anomalies on 1 August. Together, these results both demonstrate a significant advance in the skill of seasonal forecasts of the Southern Hemisphere and highlight the importance of accurate modeling and observation of the stratosphere in producing long-range forecasts.

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The Life Cycle and Variability of Antarctic Weak Polar Vortex Events

Journal of Climate ◽

10.1175/jcli-d-21-0500.1 ◽

2022 ◽

pp. 1-63

Keyword(s):

Life Cycle ◽

Polar Vortex ◽

Southern Annular Mode ◽

Austral Spring ◽

Stratospheric Polar Vortex ◽

Temperature And Precipitation ◽

Scale Temperature ◽

Precipitation Anomalies ◽

Polar Stratosphere ◽

The Antarctic

Abstract Motivated by the strong Antarctic sudden stratospheric warming (SSW) in 2019, a survey on the similar Antarctic weak polar events (WPV) is presented, including their life cycle, dynamics, seasonality, and climatic impacts. The Antarctic WPVs have a frequency of about four events per decade, with the 2002 event being the only major SSW. They show a similar life cycle to the SSWs in the Northern Hemisphere but have a longer duration. They are primarily driven by enhanced upward-propagating wavenumber 1 in the presence of a preconditioned polar stratosphere, i.e., a weaker and more contracted Antarctic stratospheric polar vortex. Antarctic WPVs occur mainly in the austral spring. Their early occurrence is preceded by an easterly anomaly in the middle and upper equatorial stratosphere besides the preconditioned polar stratosphere. The Antarctic WPVs increase the ozone concentration in the polar region and are associated with an advanced seasonal transition of the stratospheric polar vortex by about one week. Their frequency doubles after 2000 and is closely related to the advanced Antarctic stratospheric final warming in recent decades. The WPV-resultant negative phase of the southern annular mode descends to the troposphere and persists for about three months, leading to persistent hemispheric scale temperature and precipitation anomalies.

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Importance of Stratospheric Polar Vortex Events for Seasonal Predictability of Sea Level Pressure over the North Atlantic and Europe

10.5194/egusphere-egu2020-11067 ◽

2020 ◽

Author(s):

Johanna Baehr ◽

Simon Wett ◽

Mikhail Dobrynin ◽

Daniela Domeisen

Keyword(s):

Sea Level ◽

North Atlantic ◽

Polar Vortex ◽

Seasonal Prediction ◽

Prediction System ◽

Seasonal Predictability ◽

Stratospheric Polar Vortex ◽

Sea Level Pressure ◽

The North ◽

The North Atlantic

The downward influence of the stratosphere on the troposphere can be significant during boreal winter when the polar vortex is most variable, when major circulation changes in&#160;the stratosphere can impact the tropospheric flow. These strong and weak vortex events, the latter also referred to as Sudden Stratospheric Warmings (SSWs), are capable of influencing&#160;the tropospheric circulation down to the sea level on timescales from weeks to months. Thus, the occurrence of stratospheric polar vortex events influences the seasonal predictability of&#160;sea level pressure (SLP), which is, over the Atlantic sector, strongly linked to the North Atlantic oscillation (NAO). We analyze the influence of the polar vortex on the seasonal predictability of SLP in a seasonal prediction system based on the mixed resolution configuration of the coupled Max-Planck-Institute Earth System Model (MPI-ESM), where we investigate a 30 member ensemble hindcast simulation covering 1982 -2016. Since the state of the polar vortex is predictable only a few weeks or even days ahead, the&#160;seasonal prediction system cannot exactly predict the day of occurrence of stratospheric events. However, making use of the large number of stratospheric polar vortex events in the&#160;ensemble hindcast simulation, we present a statistical analysis of the influence of a correct or incorrect prediction of the stratospheric vortex state on the seasonal predictability of SLP&#160;over the North Atlantic and Europe.

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Predictions of the boreal winter stratosphere with the C3S multi-model seasonal forecast system

10.5194/ems2021-42 ◽

2021 ◽

Author(s):

Alice Portal ◽

Paolo Ruggieri ◽

Froila M. Palmeiro ◽

Javier Garcı́a-Serrano ◽

Daniela I. V. Domeisen ◽

...

Keyword(s):

Southern Oscillation ◽

Polar Vortex ◽

Seasonal Prediction ◽

Seasonal Forecast ◽

Wave Activity ◽

Arctic Sea Ice ◽

Mean Flow ◽

Seasonal Forecasts ◽

Stratospheric Polar Vortex ◽

Prediction Systems

As a result of the recent progress in the performance of seasonal prediction systems, forecasts of the mid-latitude weather at seasonal time scales are becoming increasingly important for societal decision making, as in risk estimate and management of meteorological extreme events. The predictability of the Northern-Hemisphere winter troposphere, especially in the Euro-Atlantic region, stems from the representation of a number of sources of predictability, notably El Nino Southern Oscillation, the stratospheric polar vortex, Arctic sea-ice extent, Eurasian snow cover. Among these, the stratospheric polar vortex is known to play a paramount role in seasonal forecasts of the winter tropospheric flow.Here, we investigate the performance in the stratosphere of five seasonal prediction systems taking part in the Copernicus Climate Change Service (C3S), with a focus on the seasonal forecast skill and variability, and on the assessment of stratospheric processes. We show that dynamical forecasts of the stratosphere initialised at the beginning of November are considerably more skilful than empirical forecasts based on observed October or November anomalies. Advances in the representation of stratospheric seasonal variability and extremes, i.e. sudden stratospheric warming frequency, are identified with respect to previous generations of climate models running roughly a decade ago. Such results display, however, a large model dependence. Finally, we stress the importance of the relation between the stratospheric wave activity and the stratospheric polar vortex (i.e. the wave&#8212;mean-flow interaction), applied both to the variability and to the predictability of the stratospheric mean flow. Indeed, forecasts of the winter stratospheric polar vortex are closely connected to the prediction of November-to-February stratospheric wave activity, in particular in the Eurasian sector.

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Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode

Scientific Reports ◽

10.1038/s41598-019-50897-4 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 6

Author(s):

W. A. Dickens ◽

G. Kuhn ◽

M. J. Leng ◽

A. G. C. Graham ◽

J. A. Dowdeswell ◽

...

Keyword(s):

Antarctic Peninsula ◽

Isotope Composition ◽

Southern Annular Mode ◽

Ice Shelf ◽

Annular Mode ◽

Ice Shelves ◽

The North ◽

North Eastern ◽

Glacial Discharge ◽

The Antarctic

Abstract The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming.

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The influence of large amplitude planetary waves on the Antarctic ozone hole of austral spring 2017

Journal of Southern Hemisphere Earth System Science ◽

10.1071/es19022 ◽

2019 ◽

Vol 69 (1) ◽

pp. 57

Author(s):

Oleksandr Evtushevsky ◽

Andrew R. Klekociuk ◽

Volodymyr Kravchenko ◽

Gennadi Milinevsky ◽

Asen Grytsai

Keyword(s):

Large Amplitude ◽

Polar Vortex ◽

Maximum Size ◽

Planetary Waves ◽

Ozone Hole ◽

Late Winter ◽

Austral Spring ◽

Stratospheric Polar Vortex ◽

Key Factor ◽

The Antarctic

Quasi-stationary planetary wave activity in the lower Antarctic stratosphere in the late austral winter was an important contributor to the preconditioning of the ozone hole in spring 2017. Observations show that the ozone hole area (OHA) in spring 2017 was at the level of 1980s, that is, almost half the maximum size in 2000s. The observed OHA was close to that forecasted based on a least-squares linear regression between wave amplitude in August and OHA in September–November. We show that the key factor which contributed to the preconditioning of the Antarctic stratosphere for a relatively small ozone hole in the spring of 2017 was the development of large-amplitude stratospheric planetary waves of zonal wave numbers 1 and 2 in late winter. The waves likely originated from tropospheric wave trains and promoted the development of strong mid-latitude anticyclones in the lower stratosphere which interacted with the stratospheric polar vortex and strongly eroded the vortex in August and September, mitigating the overall level of ozone loss.

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Evolution of the eastward shift in the quasi-stationary minimum of the Antarctic total ozone column

10.5194/acp-2016-537 ◽

2016 ◽

Author(s):

Asen Grytsai ◽

Gennadi Milinevsky ◽

Andrew Klekociuk ◽

Oleksandr Evtushevsky

Keyword(s):

Ozone Depletion ◽

Total Ozone ◽

Regional Climate ◽

Southern Annular Mode ◽

Reanalysis Data ◽

Austral Spring ◽

Annular Mode ◽

Antarctic Ozone ◽

The Antarctic ◽

Ozone Column

Abstract. The quasi-stationary pattern of the Antarctic total ozone has changed during the last four decades, demonstrating an eastward shift in the zonal ozone minimum. In this work, the association between the longitudinal shift of the zonal ozone minimum and changes in meteorological fields in austral spring (September–November) for 1979–2014 is analyzed. Regressive, correlative and anomaly composite analyses are applied to reanalysis data. Patterns of the Southern Annular Mode and quasi-stationary zonal waves 1 and 3 in the meteorological fields show relationships with interannual variability in the longitude of the zonal ozone minimum. On decadal time scales, consistent longitudinal shifts of the zonal ozone minimum and zonal wave 3 pattern in the middle troposphere temperature at the southern mid-latitudes are shown. As known, Antarctic ozone depletion in spring is strongly projected on the Southern Annular Mode in summer and impacts tropospheric climate. The results of this study suggest that changes in zonal ozone asymmetry accompanying the ozone depletion could be associated with regional climate changes in the Southern Hemisphere in spring.

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Evolution of the eastward shift in the quasi-stationary minimum of the Antarctic total ozone column

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-1741-2017 ◽

2017 ◽

Vol 17 (3) ◽

pp. 1741-1758 ◽

Cited By ~ 7

Author(s):

Asen Grytsai ◽

Andrew Klekociuk ◽

Gennadi Milinevsky ◽

Oleksandr Evtushevsky ◽

Kane Stone

Keyword(s):

Southern Hemisphere ◽

Ozone Depletion ◽

Total Ozone ◽

Regional Climate ◽

Southern Annular Mode ◽

Reanalysis Data ◽

Austral Spring ◽

Annular Mode ◽

Ozone Depleting Substances ◽

The Antarctic

Abstract. The quasi-stationary pattern of the Antarctic total ozone has changed during the last 4 decades, showing an eastward shift in the zonal ozone minimum. In this work, the association between the longitudinal shift of the zonal ozone minimum and changes in meteorological fields in austral spring (September–November) for 1979–2014 is analyzed using ERA-Interim and NCEP–NCAR reanalyses. Regressive, correlative and anomaly composite analyses are applied to reanalysis data. Patterns of the Southern Annular Mode and quasi-stationary zonal waves 1 and 3 in the meteorological fields show relationships with interannual variability in the longitude of the zonal ozone minimum. On decadal timescales, consistent longitudinal shifts of the zonal ozone minimum and zonal wave 3 pattern in the middle-troposphere temperature at the southern midlatitudes are shown. Attribution runs of the chemistry–climate version of the Australian Community Climate and Earth System Simulator (ACCESS-CCM) model suggest that long-term shifts of the zonal ozone minimum are separately contributed by changes in ozone-depleting substances and greenhouse gases. As is known, Antarctic ozone depletion in spring is strongly projected on the Southern Annular Mode in summer and impacts summertime surface climate across the Southern Hemisphere. The results of this study suggest that changes in zonal ozone asymmetry accompanying ozone depletion could be associated with regional climate changes in the Southern Hemisphere in spring.

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The 2019 Southern Hemisphere stratospheric polar vortex weakening and its impacts

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-20-0112.1 ◽

2021 ◽

pp. 1-50

Author(s):

Eun-Pa Lim ◽

Harry H. Hendon ◽

Amy H. Butler ◽

David W. J. Thompson ◽

Zachary Lawrence ◽

...

Keyword(s):

Southern Hemisphere ◽

Polar Vortex ◽

Austral Spring ◽

Stratospheric Polar Vortex ◽

Climate Conditions ◽

Extreme Climate ◽

The Antarctic

Capsule SummaryDuring austral spring 2019 the Antarctic stratosphere experienced record-breaking warming and a near-record polar vortex weakening, resulting in predictable extreme climate conditions throughout the Southern Hemisphere through December 2019.

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Seasonal prediction of the boreal winter stratosphere

Climate Dynamics ◽

10.1007/s00382-021-05787-9 ◽

2021 ◽

Author(s):

Alice Portal ◽

Paolo Ruggieri ◽

Froila M. Palmeiro ◽

Javier García-Serrano ◽

Daniela I. V. Domeisen ◽

...

Keyword(s):

Southern Oscillation ◽

Polar Vortex ◽

Seasonal Prediction ◽

Wave Activity ◽

Boreal Winter ◽

Quasi Biennial Oscillation ◽

Stratospheric Polar Vortex ◽

Eddy Heat Flux ◽

Prediction Systems ◽

Model Database

AbstractThe predictability of the Northern Hemisphere stratosphere and its underlying dynamics are investigated in five state-of-the-art seasonal prediction systems from the Copernicus Climate Change Service (C3S) multi-model database. Special attention is devoted to the connection between the stratospheric polar vortex (SPV) and lower-stratosphere wave activity (LSWA). We find that in winter (December to February) dynamical forecasts initialised on the first of November are considerably more skilful than empirical forecasts based on October anomalies. Moreover, the coupling of the SPV with mid-latitude LSWA (i.e., meridional eddy heat flux) is generally well reproduced by the forecast systems, allowing for the identification of a robust link between the predictability of wave activity above the tropopause and the SPV skill. Our results highlight the importance of November-to-February LSWA, in particular in the Eurasian sector, for forecasts of the winter stratosphere. Finally, the role of potential sources of seasonal stratospheric predictability is considered: we find that the C3S multi-model overestimates the stratospheric response to El Niño–Southern Oscillation (ENSO) and underestimates the influence of the Quasi–Biennial Oscillation (QBO).

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The Impact of ENSO on Wave Breaking and Southern Annular Mode Events

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3311.1 ◽

2010 ◽

Vol 67 (9) ◽

pp. 2854-2870 ◽

Cited By ~ 47

Author(s):

Tingting Gong ◽

Steven B. Feldstein ◽

Dehai Luo

Keyword(s):

El Niño ◽

Wave Breaking ◽

El Nino ◽

Southern Annular Mode ◽

La Niña ◽

Background Flow ◽

Austral Spring ◽

Annular Mode ◽

La Nina ◽

The Impact

Abstract This study examines the relationship between intraseasonal southern annular mode (SAM) events and the El Niño–Southern Oscillation (ENSO) using daily 40-yr ECMWF Re-Analysis (ERA-40) data. The data coverage spans the years 1979–2002, for the austral spring and summer seasons. The focus of this study is on the question of why positive SAM events dominate during La Niña and negative SAM events during El Niño. A composite analysis is performed on the zonal-mean zonal wind, Eliassen–Palm fluxes, and two diagnostic variables: the meridional potential vorticity gradient, a zonal-mean quantity that is used to estimate the likelihood of wave breaking, and the wave breaking index (WBI), which is used to evaluate the strength of the wave breaking. The results of this investigation suggest that the background zonal-mean flow associated with La Niña (El Niño) is preconditioned for strong (weak) anticyclonic wave breaking on the equatorward side of the eddy-driven jet, the type of wave breaking that is found to drive positive (negative) SAM events. A probability density function analysis of the WBI, for both La Niña and El Niño, indicates that strong anticyclonic wave breaking takes place much more frequently during La Niña and weak anticyclonic wave breaking during El Niño. It is suggested that these wave breaking characteristics, and their dependency on the background flow, can explain the strong preference for SAM events of one phase during ENSO. The analysis also shows that austral spring SAM events that coincide with ENSO are preceded by strong stratospheric SAM anomalies and then are followed by a prolonged period of wave breaking that lasts for approximately 30 days. These findings suggest that the ENSO background flow also plays a role in the excitation of stratospheric SAM anomalies and that the presence of these stratospheric SAM anomalies in turn excites and then maintains the tropospheric SAM anomalies via a positive eddy feedback.

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