scholarly journals Nonstationarity in Southern Hemisphere Climate Variability Associated with the Seasonal Breakdown of the Stratospheric Polar Vortex

2017 ◽  
Vol 30 (18) ◽  
pp. 7125-7139 ◽  
Author(s):  
Nicholas J. Byrne ◽  
Theodore G. Shepherd ◽  
Tim Woollings ◽  
R. Alan Plumb
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Seasonal Cycle ◽  
Vortex Breakdown ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Early Summer ◽  
Stratospheric Polar Vortex ◽  
Time Symmetry

Abstract Statistical models of climate generally regard climate variability as anomalies about a climatological seasonal cycle, which are treated as a stationary stochastic process plus a long-term seasonally dependent trend. However, the climate system has deterministic aspects apart from the climatological seasonal cycle and long-term trends, and the assumption of stationary statistics is only an approximation. The variability of the Southern Hemisphere zonal-mean circulation in the period encompassing late spring and summer is an important climate phenomenon and has been the subject of numerous studies. It is shown here, using reanalysis data, that this variability is rendered highly nonstationary by the organizing influence of the seasonal breakdown of the stratospheric polar vortex, which breaks time symmetry. It is argued that the zonal-mean tropospheric circulation variability during this period is best viewed as interannual variability in the transition between the springtime and summertime regimes induced by variability in the vortex breakdown. In particular, the apparent long-term poleward jet shift during the early-summer season can be more simply understood as a delay in the equatorward shift associated with this regime transition. The implications of such a perspective for various open questions are discussed.

The Impact of Stratospheric Ozone Changes on Downward Wave Coupling in the Southern Hemisphere*

2011 ◽  
Vol 24 (16) ◽  
pp. 4210-4229 ◽  
Author(s):  
Tiffany A. Shaw ◽  
Judith Perlwitz ◽  
Nili Harnik ◽  
Paul A. Newman ◽  
Steven Pawson
Keyword(s):  
Southern Hemisphere ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Coupling Model ◽  
Reanalysis Data ◽  
Early Summer ◽  
Stratospheric Polar Vortex ◽  
Wave Coupling ◽  
The Impact

Abstract The impact of stratospheric ozone changes on downward wave coupling between the stratosphere and troposphere in the Southern Hemisphere is investigated using a suite of Goddard Earth Observing System chemistry–climate model (GEOS CCM) simulations. Downward wave coupling occurs when planetary waves reflected in the stratosphere impact the troposphere. In reanalysis data, the climatological coupling occurs from September to December when the stratospheric basic state has a well-defined high-latitude meridional waveguide in the lower stratosphere that is bounded above by a reflecting surface, called a bounded wave geometry. Reanalysis data suggests that downward wave coupling during November–December has increased during the last three decades. The GEOS CCM simulation of the recent past captures the main features of downward wave coupling in the Southern Hemisphere. Consistent with the Modern Era Retrospective-Analysis for Research and Application (MERRA) dataset, wave coupling in the model maximizes during October–November when there is a bounded wave geometry configuration. However, the wave coupling in the model is stronger than in the MERRA dataset, and starts earlier and ends later in the seasonal cycle. The late season bias is caused by a bias in the timing of the stratospheric polar vortex breakup. Temporal changes in stratospheric ozone associated with past depletion and future recovery significantly impact downward wave coupling in the model. During the period of ozone depletion, the spring bounded wave geometry, which is favorable for downward wave coupling, extends into early summer, due to a delay in the vortex breakup date, and leads to increased downward wave coupling during November–December. During the period of ozone recovery, the stratospheric basic state during November–December shifts from a spring configuration back to a summer configuration, where waves are trapped in the troposphere, and leads to a decrease in downward wave coupling. Model simulations with chlorine fixed at 1960 values and increasing greenhouse gases show no significant changes in downward wave coupling and confirm that the changes in downward wave coupling in the model are caused by ozone changes. The results reveal a new mechanism wherein stratospheric ozone changes can affect the tropospheric circulation.

scholarly journals A simple kinematic model for the Lagrangian description of relevant nonlinear processes in the stratospheric polar vortex

2017 ◽  
Vol 24 (2) ◽  
pp. 265-278 ◽  
Author(s):  
Víctor José García-Garrido ◽  
Jezabel Curbelo ◽  
Carlos Roberto Mechoso ◽  
Ana María Mancho ◽  
Stephen Wiggins
Keyword(s):  
Vortex Breakdown ◽  
Kinematic Model ◽  
Axisymmetric Flow ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Lagrangian Description ◽  
Stratospheric Polar Vortex ◽  
Fourier Decomposition ◽  
Complex Fluid ◽  
Hyperbolic Trajectories

Abstract. In this work, we study the Lagrangian footprint of the planetary waves present in the Southern Hemisphere stratosphere during the exceptional sudden Stratospheric warming event that took place during September 2002. Our focus is on constructing a simple kinematic model that retains the fundamental mechanisms responsible for complex fluid parcel evolution, during the polar vortex breakdown and its previous stages. The construction of the kinematic model is guided by the Fourier decomposition of the geopotential field. The study of Lagrangian transport phenomena in the ERA-Interim reanalysis data highlights hyperbolic trajectories, and these trajectories are Lagrangian objects that are the kinematic mechanism for the observed filamentation phenomena. Our analysis shows that the breaking and splitting of the polar vortex is justified in our model by the sudden growth of a planetary wave and the decay of the axisymmetric flow.

scholarly journals Evolution of the stratospheric polar vortex edge intensity and duration in the Southern hemisphere over the 1979–2020 period

2021 ◽  
Author(s):  
Audrey Lecouffe ◽  
Sophie Godin-Beekmann ◽  
Andrea Pazmiño ◽  
Alain Hauchecorne
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Onset Date ◽  
Late Winter ◽  
Stratospheric Polar Vortex ◽  
The Difference ◽  
Lower Variability

Abstract. The intensity and position of the Southern Hemisphere stratospheric polar vortex edge is evaluated as a function of equivalent latitude over the 1979–2020 period on three isentropic levels (475 K, 550 K and 675 K) from ECMWF ERA-Interim reanalysis. The study also includes an analysis of the onset and breakup dates of the polar vortex, which are determined from wind thresholds (e.g. 15.2 m.s−1, 20 m.s−1and 25 m.s−1) along the vortex edge. The vortex edge is stronger in late winter, over September–October – November with the period of strongest intensity occurring later at the lowermost level. A lower variability of the edge position is observed during the same period. Long-term increase of the vortex edge intensity and break-up date is observed over the 1979–1999 period, linked to the increase of the ozone hole. Long-term decrease of the vortex onset date related to the 25 m.s−1wind threshold is also observed at 475 K during this period. The solar cycle and to a lower extent the quasi-biennal oscillation (QBO) and El Niño Southern Oscillation (ENSO) modulate the inter-annual evolution of the strength of the vortex edge and the vortex breakup dates. Stronger vortex edge and longer vortex duration is observed in solar minimum (minSC) years, with the QBO and ENSO further modulating the solar cycle influence, especially at 475 K and 550 K: during West QBO (wQBO) phases, the difference between vortex edge intensity for minSC and maxSC years is smaller than during East QBO (eQBO) phases. The polar vortex edge is stronger and lasts longer for maxSC/wQBO years than for maxSC/eQBO years. ENSO has a weaker impact but the vortex edge is somewhat stronger during cold ENSO phases for both minSC and maxSC years.

An Observational Study of the Final Breakdown of the Southern Hemisphere Stratospheric Vortex in 2002

2005 ◽  
Vol 62 (3) ◽  
pp. 735-747 ◽  
Author(s):  
Yvan J. Orsolini ◽  
Cora E. Randall ◽  
Gloria L. Manney ◽  
Douglas R. Allen
Keyword(s):  
Southern Hemisphere ◽  
Vortex Core ◽  
Vortex Breakdown ◽  
Michelson Interferometer ◽  
European Space Agency ◽  
Polar Vortex ◽  
Stratospheric Aerosol ◽  
Satellite Observations ◽  
Stratospheric Polar Vortex ◽  
Space Agency

Abstract The 2002 Southern Hemisphere final warming occurred early, following an unusually active winter and the first recorded major warming in the Antarctic. The breakdown of the stratospheric polar vortex in October and November 2002 is examined using new satellite observations from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument aboard the European Space Agency (ESA) Environment Satellite (ENVISAT) and meteorological analyses, both high-resolution fields from the European Centre for Medium-Range Weather Forecasts and the coarser Met Office analyses. The results derived from MIPAS observations are compared to measurements and inferences from well-validated solar occultation satellite instruments [Halogen Occultation Experiment (HALOE), Polar Ozone and Aerosol Measurement III (POAM III), and Stratospheric Aerosol and Gas Experiments II and III (SAGE II and III)] and to finescale tracer fields reconstructed by transporting trace gases based on MIPAS or climatological data using a reverse-trajectory method. These comparisons confirm the features in the MIPAS data and the interpretation of the evolution of the flow during the vortex decay revealed by those features. Mapped ozone and water vapor from MIPAS and the analyzed isentropic potential vorticity vividly display the vortex breakdown, which occurred earlier than usual. A large tongue of vortex air was pulled out westward and coiled up in an anticyclone, while the vortex core remnant shrank and drifted eastward and equatorward over the South Atlantic. By roughly mid-November, the vortex remnant at 10 mb had shrunk below scales resolved by the satellite observations, while a vortex core remained in the lower stratosphere.

scholarly journals Stratosphere–Troposphere Coupling in the Southern Hemisphere

2005 ◽  
Vol 62 (3) ◽  
pp. 708-715 ◽  
Author(s):  
David W. J. Thompson ◽  
Mark P. Baldwin ◽  
Susan Solomon
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Temporal Evolution ◽  
Polar Vortex ◽  
Climate Impacts ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Polar Vortex ◽  
Tropospheric Circulation ◽  
Stratospheric Variability

Abstract This study examines the temporal evolution of the tropospheric circulation following large-amplitude variations in the strength of the Southern Hemisphere (SH) stratospheric polar vortex in data from 1979 to 2001 and following the SH sudden stratospheric warming of 2002. In both cases, anomalies in the strength of the SH stratospheric polar vortex precede similarly signed anomalies in the tropospheric circulation that persist for more than 2 months. The SH tropospheric circulation anomalies reflect a bias in the polarity of the SH annular mode (SAM), a large-scale pattern of climate variability characterized by fluctuations in the strength of the SH circumpolar flow. Consistent with the climate impacts of the SAM, variations in the stratospheric polar vortex are also followed by coherent changes in surface temperatures throughout much of Antarctica. The results add to a growing body of evidence that suggests that stratospheric variability plays an important role in driving climate variability at Earth’s surface on a range of time scales.

Stratosphere–Troposphere Coupling during Spring Onset

2006 ◽  
Vol 19 (19) ◽  
pp. 4891-4901 ◽  
Author(s):  
Robert X. Black ◽  
Brent A. McDaniel ◽  
Walter A. Robinson
Keyword(s):  
North Atlantic ◽  
High Latitude ◽  
Seasonal Cycle ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Lower Boundary ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
Near Surface ◽  
Circulation Anomalies

Abstract The authors perform an observational study of the relation between stratospheric final warmings (SFWs) and the boreal extratropical circulation. SFW events are found to provide a strong organizing influence upon the large-scale circulation of the stratosphere and troposphere during the period of spring onset. In contrast to the climatological seasonal cycle, SFW events noticeably sharpen the annual weakening of high-latitude circumpolar westerlies in both the stratosphere and troposphere. A coherent pattern of significant westerly (easterly) zonal wind anomalies is observed to extend from the stratosphere to the earth’s surface at high latitudes prior to (after) SFW events, coinciding with the polar vortex breakdown. This evolution is associated with a bidirectional dynamical coupling of the stratosphere–troposphere system in which tropospheric low-frequency waves induce annular stratospheric circulation anomalies, which in turn, are followed by annular tropospheric circulation anomalies. The regional tropospheric manifestation of SFW events consists of a North Atlantic Oscillation (NAO)-like phase transition in the near-surface geopotential height field, with height rises over polar latitudes and height falls over the northeast North Atlantic. This lower-tropospheric change pattern is distinct from the climatological seasonal cycle, which closely follows seasonal trends in thermal forcing at the lower boundary. Although broadly similar, the tropospheric anomaly patterns identified in the study do not precisely correspond to the canonical northern annular mode (NAM) and NAO patterns as the primary anomaly centers are retracted northward toward the pole. The results here imply that (i) high-latitude climate may be particularly sensitive to long-term trends in the annual cycle of the stratospheric polar vortex and (ii) improvements in the understanding and simulation of SFW events may benefit medium-range forecasts of spring onset in the extratropics.

The Role of Stratospheric Polar Vortex Breakdown in Southern Hemisphere Climate Trends

2014 ◽  
Vol 71 (7) ◽  
pp. 2335-2353 ◽  
Author(s):  
Lantao Sun ◽  
Gang Chen ◽  
Walter A. Robinson
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Climate Model ◽  
Vortex Breakdown ◽  
Polar Vortex ◽  
Wave Drag ◽  
Hadley Cell ◽  
Climate Trends ◽  
Stratospheric Polar Vortex

Abstract This paper investigates the connection between the delay in the final breakdown of the stratospheric polar vortex, the stratospheric final warming (SFW), and Southern Hemisphere climate trends. The authors first analyze Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) and three climate model outputs with different climate forcings. Climate trends appear when there is a delay in the timing of SFWs. When regressed onto the SFW dates (which reflect the anomaly when the SFW is delayed for one standard deviation of its onset dates), the anomaly pattern bears a resemblance to the observed climate trends, for all the model outputs, even without any trends. This suggests that the stratospheric and tropospheric circulations are organized by the timing of SFWs in both the interannual time scale and climate trends because of external forcings. The authors further explore the role of the SFW using a simplified dynamical model in which the ozone depletion is mimicked by a springtime polar stratospheric cooling. The responses of zonal-mean atmospheric circulation, including zonal wind, temperature, and poleward edge of the Hadley cell and the Ferrel cell, are similar to the observed climate trends. The authors divide the years into those in which the SFW is delayed and those in which it is not. The responses for the years in which the SFW is delayed are very similar to the overall response, while the stratosphere is only characterized by the localized cooling for those years in which the SFW is not delayed, with no subsequent downward influence into the troposphere. This suggests that, in order to affect the troposphere, ozone depletion must first delay the SFW so as to induce a deep response in planetary wave drag and the associated eddy-driven circulation.

scholarly journals Southern Hemisphere atmospheric blocking diagnostic by ECMWF and NCEP/NCAR data

2012 ◽  
Vol 27 (3) ◽  
pp. 263-271 ◽  
Author(s):  
Monica Cristina Damião Mendes ◽  
Iracema F. A. Cavalcanti ◽  
Dirceu Luis Herdies
Keyword(s):  
Atlantic Ocean ◽  
Southern Hemisphere ◽  
Geopotential Height ◽  
Seasonal Cycle ◽  
South Pacific ◽  
Reanalysis Data ◽  
Data Sets ◽  
Atmospheric Blocking ◽  
Assimilation Scheme

An assessment of blocking episodes over the Southern Hemisphere, selected from the Era-40 and NCEP/NCAR reanalysis are presented in this study. Blocking can be defined by an objective index based on two 500 hPa geopotential height meridional gradients. The seasonal cycle and preferential areas of occurrence are well reproduced by the two data sets. In both reanalysis used in this study, South Pacific and Oceania were the preferred regions for blocking occurrence, followed by the Atlantic Ocean. However the results revealed differences in frequencies of occurrences, which may be related to the choice of assimilation scheme employed to produce the reanalysis data sets. It is important to note that the ERA 40 and NCEP/NCAR reanalysis were produced using consistent models and assimilation schemes throughout the whole reanalyzed period, which are different for each set.

scholarly journals Long-Term and Seasonal Trends in Global Wave Height Extremes Derived from ERA-5 Reanalysis Data

2020 ◽  
Vol 8 (12) ◽  
pp. 1015
Author(s):  
Alicia Takbash ◽  
Ian R. Young
Keyword(s):  
Southern Hemisphere ◽  
Wave Height ◽  
Significant Wave Height ◽  
Reanalysis Data ◽  
Extreme Value Analysis ◽  
Winter Storms ◽  
Value Analysis ◽  
Weather Forecasts ◽  
Significant Wave

A non-stationary extreme value analysis of 41 years (1979–2019) of global ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis) significant wave height data is undertaken to investigate trends in the values of 100-year significant wave height, Hs100. The analysis shows that there has been a statistically significant increase in the value of Hs100 over large regions of the Southern Hemisphere. There have also been smaller decreases in Hs100 in the Northern Hemisphere, although the related trends are generally not statistically significant. The increases in the Southern Hemisphere are a result of an increase in either the frequency or intensity of winter storms, particularly in the Southern Ocean.

scholarly journals A meridional structure of static stability and ozone vertical gradient around the tropopause in the Southern Hemisphere extratropics

2010 ◽  
Vol 10 (8) ◽  
pp. 19175-19194 ◽  
Author(s):  
Y. Tomikawa ◽  
T. Yamanouchi
Keyword(s):  
Southern Hemisphere ◽  
Seasonal Variations ◽  
Inversion Layer ◽  
Polar Vortex ◽  
Vertical Gradient ◽  
Static Stability ◽  
Radiative Heating ◽  
Stratospheric Polar Vortex ◽  
Close Relationship ◽  
The Antarctic

Abstract. An analysis of the static stability and ozone vertical gradient in the ozone tropopause based (OTB) coordinate is applied to the ozonesonde data at 10 stations in the Southern Hemisphere (SH) extratropics. The tropopause inversion layer (TIL) with a static stability maximum just above the tropopause shows similar seasonal variations at two Antarctic stations, which are latitudinally far from each other. Since the sunshine hour varies with time in a quite different way between these two stations, it implies that the radiative heating due to solar ultraviolet absorption of ozone does not contribute to the seasonal variation of the TIL. A meridional section of the static stability in the OTB coordinate shows that the static stability just above the tropopause has a large latitudinal gradient between 60° S and 70° S in austral winter because of the absence of the TIL over the Antarctic. It is accompanied by an increase of westerly shear with height above the tropopause, so that the polar-night jet is formed above this latitude region. This result suggests a close relationship between the absence of the TIL and the stratospheric polar vortex in the Antarctic winter. A vertical gradient of ozone mixing ratio, referred to as ozone vertical gradient, around the tropopause shows similar latitudinal and seasonal variations with the static stability in the SH extratropics. In a height region above the TIL, a small ozone vertical gradient in the midlatitudes associated with the Antarctic ozone hole is observed in a height region of the subvortex but not around the polar vortex. This is a clear evidence of active latitudinal mixing between the midlatitudes and subvortex.

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