Stratospheric influence on idealised baroclinic life cycles

Shift Response ◽

Wave Development ◽

Final Steady State ◽

Numerical Model Experiments

The importance of understanding the dynamical coupling of troposphere and stratosphere to make accurate weather and climate predictions is well-known. Over the past years and decades various signatures of such a coupling have been discovered. A very robust result, for example, seems to be an equatorward shift of the tropospheric eddy driven jet following sudden stratospheric warming events, where the westerly winds of the stratospheric polar vortex weaken or even reverse. However, many aspects of this fundamental coupling are still not fully understood and research on how the state of the stratosphere can influence the tropospheric circulation and what dynamical processes are involved is still ongoing. An important such process arises due to the interaction of a sharp, localised maximum in potential vorticity gradient near the tropopause with baroclinic eddies in the troposphere. Here, we analyse the sensitivity of baroclinic wave development and evolution to changes of various basic state characteristics, by performing a series of idealised baroclinic eddy life cycle experiments. Special attention is paid to sensitivities associated with the dynamical state of the stratosphere. We find that the final (steady) state of the life cycle simulations corresponds to an equatorward shift of the tropospheric jet in cases where the initial conditions do not include a stratospheric polar vortex (such as following sudden warming events) compared to those that do. These results further support the idea that the stratospheric state can strongly influence tropospheric dynamics and, in particular, highlight the robustness of the jet shift response following sudden warmings, that can be seen in a range of observations and numerical model experiments.

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 ◽

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.

Sensitivity of the Tropospheric Circulation to Changes in the Strength of the Stratospheric Polar Vortex

Monthly Weather Review ◽

10.1175/mwr3178.1 ◽

2006 ◽

Vol 134 (8) ◽

pp. 2191-2207 ◽

Cited By ~ 25

Author(s):

Thomas Jung ◽

Jan Barkmeijer

Keyword(s):

North Atlantic ◽

Polar Vortex ◽

The North ◽

European Area ◽

Extended Range ◽

The North Atlantic Oscillation ◽

Ecmwf Model ◽

Strong Vortex

Abstract The sensitivity of the wintertime tropospheric circulation to changes in the strength of the Northern Hemisphere stratospheric polar vortex is studied using one of the latest versions of the ECMWF model. Three sets of experiments were carried out: one control integration and two integrations in which the strength of the stratospheric polar vortex has been gradually reduced and increased, respectively, during the course of the integration. The strength of the polar vortex is changed by applying a forcing to the model tendencies in the stratosphere only. The forcing has been obtained using the adjoint technique. It is shown that, in the ECMWF model, changes in the strength of the polar vortex in the middle and lower stratosphere have a significant and slightly delayed (on the order of days) impact on the tropospheric circulation. The tropospheric response shows some resemblance to the North Atlantic Oscillation (NAO), though the centers of action are slightly shifted toward the east compared to those of the NAO. Furthermore, a separate comparison of the response to a weak and strong vortex forcing suggests that to first order the tropospheric response is linear within a range of realistic stratospheric perturbations. From the results presented, it is argued that extended-range forecasts in the European area particularly benefit from the stratosphere–troposphere link.

Origins of Multi-decadal Variability in Sudden Stratospheric Warmings

10.5194/egusphere-egu21-1509 ◽

2021 ◽

Author(s):

Oscar Dimdore-Miles ◽

Lesley Gray ◽

Scott Osprey

Keyword(s):

Decadal Variability ◽

Low Frequency ◽

Polar Vortex ◽

Major Influence ◽

Quasi Biennial Oscillation ◽

Surface Climate ◽

Tropical Sea

Sudden Stratospheric Warmings (SSWs) are major disruptions of the Northern Hemisphere (NH) stratospheric polar vortex and occur on average approximately 6 times per decade in observation based records. However, within these records, intervals of significantly higher and lower SSW rates are observed suggesting the possibility of low frequency variations in event occurrence. A better understanding of factors that influence this decadal variability may help to improve predictability of NH mid-latitude surface climate, through stratosphere-troposphere coupling. In this work, multi-decadal variability of SSW events is examined in a 1000-yr pre-industrial simulation of a coupled Atmosphere-Ocean-Land-Sea ice model. Using a wavelet spectral decomposition method, we show that hiatus events (intervals of a decade or more with no SSWs) and consecutive SSW events (extended intervals with at least one SSW in each year) vary on multi-decadal timescales of period between 60 and 90 years. Signals on these timescales are present for approximately 450 years of the simulation. We investigate the possible source of these long-term signals and find that the direct impact of variability in tropical sea surface temperatures, as well as the associated Aleutian Low, can account for only a small portion of the SSW variability. Instead, the major influence on long-term SSW variability is associated with long-term variability in amplitude of the stratospheric quasi biennial oscillation (QBO). The QBO influence is consistent with the well known Holton-Tan relationship, with SSW hiatus intervals associated with extended periods of particularly strong, deep QBO westerly phases. The results support recent studies that have highlighted the role of vertical coherence in the QBO when considering coupling between the QBO, the polar vortex and tropospheric circulation.

The Combined Influence of the Stratospheric Polar Vortex and ENSO on Zonal Asymmetries in the Southern Hemisphere Upper Tropospheric Circulation during Austral Spring and Summer

10.5194/egusphere-egu21-5311 ◽

2021 ◽

Author(s):

Marisol Osman ◽

Theodore Shepherd ◽

Carolina Vera

Keyword(s):

Southern Hemisphere ◽

Southern Oscillation ◽

Polar Vortex ◽

Austral Spring ◽

Wave Source ◽

Weather Forecasts ◽

Rossby Wave Source ◽

Enso Teleconnections ◽

Tropospheric Circulation

The influence of El Nin&#771;o Southern Oscillation (ENSO) and the Stratospheric Polar Vortex (SPV) on the zonal asymmetries in the Southern Hemisphere atmospheric circulation during spring and summer is examined. The main objective is to explore if the SPV can modulate the ENSO teleconnections in the extratropics. We use a large ensemble of seasonal hindcasts from the European Centre for Medium-Range Weather Forecasts Integrated Forecast System to provide a much larger sample size than is possible from the observations alone.We find a small but statistically significant relationship between ENSO and the SPV, with El Nin&#771;o events occurring with weak SPV and La Nin&#771;a events occurring with strong SPV more often than expected by chance, in agreement with previous works. We show that the zonally asymmetric response to ENSO and SPV can be mainly explained by a linear combination of the response to both forcings, and that they can combine constructively or destructively. From this perspective, we find that the tropospheric asymmetries in response to ENSO are more intense when El Nin&#771;o events occur with weak SPV and La Nin&#771;a events occur with strong SPV, at least from September through December. In the stratosphere, the ENSO teleconnections are mostly confounded by the SPV signal. The analysis of Rossby Wave Source and of wave activity shows that both are stronger when El Nin&#771;o events occur together with weak SPV, and when La Nin&#771;a events occur together with strong SPV.

Arctic Oscillation impact on thermal regime in the Eastern part of the Baltic region

Solar-Terrestrial Physics ◽

10.12737/19881 ◽

2016 ◽

Vol 2 (1) ◽

pp. 89-96

Author(s):

Индре Гечайте ◽

Indre Gecaite ◽

Александр Погорельцев ◽

Aleksandr Pogoreltsev ◽

Александр Угрюмов ◽

...

Keyword(s):

Atmospheric Circulation ◽

Geomagnetic Activity ◽

Large Scale ◽

Arctic Oscillation ◽

Polar Vortex ◽

Baltic Region ◽

Weather Forecasts ◽

The Baltic

The paper presents statistical estimations of Arctic Oscillation (AO) impact on air temperature regime in the eastern part of the Baltic region. The region is characterized by high inter-annual and inter-seasonal variability. It is important to note that in the region of global warming extremely low winter temperatures can be observed on the European territory of Russia. AO is one of the large-scale global patterns of atmospheric circulation closely associated with weather variability in northern Europe. AО anomalies occur in the upper atmosphere (stratosphere) and only then are transferred to tropospheric lower layers. The anomalies can persist over a long period of time (up to two months); so they can serve as precursors in long-range weather forecasts. In turn, changes in stratospheric polar vortex and sudden stratospheric warmings can be related to geomagnetic activity. Perhaps geomagnetic activity influences the meridional temperature gradient and then changes the structure of the stratospheric zonal wind. These changes have an effect on the tropospheric circulation. The stratosphere–troposphere coupling takes place during winter months. Therefore, the paper deals with extremely cold winter anomalies in the eastern part of the Baltic Sea region. At the same time, we examine atmospheric circulation peculiarities associated with AO phase change. We analyze data for 1951–2014.

Exploring the Tropospheric Response to Stratospheric Variability Using Lagged Quantile Regression

10.5194/egusphere-egu21-15446 ◽

2021 ◽

Author(s):

Kathrin Finke ◽

Abdel Hannachi

Keyword(s):

Quantile Regression ◽

Conditional Distribution ◽

Polar Vortex ◽

Supplementary Information ◽

Reanalysis Dataset ◽

Response Variable ◽

The Impact ◽

Stratospheric Variability

Stratospheric variability has become increasingly popular due to its potential impact on the tropospheric circulation. Extreme states of the stratospheric polar vortex have been associated with reoccurring tropospheric weather patterns more than 2-3 weeks after the initial stratospheric signal. Standard linear regression methods used to assess the statistical stratosphere-troposphere connection estimate the distribution's mean effect of a stratospheric variable as a predictor on a tropospheric response variable. However, &#160;supplementary information of the impact of extreme stratospheric behavior is hidden in the tails of the distribution, revealing a different behavior than the mean. Therefore, we use quantile regression, a method that enables us to model the complete conditional distribution of the response variable. This presentation explores various quantiles of the conditional distribution to investigate the impact of stratospheric variability on the tropospheric circulation using the ERA5 reanalysis dataset. Comparison between (lagged) linear and (lagged) quantile regression reveals significant differences making the latter method a neat tool that offers valuable information about the statistical connection between the stratosphere and the troposphere.

Stratosphere–Troposphere Coupling in the Southern Hemisphere

Journal of the Atmospheric Sciences ◽

10.1175/jas-3321.1 ◽

2005 ◽

Vol 62 (3) ◽

pp. 708-715 ◽

Cited By ~ 129

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 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.

The Downward Influence of Uncertainty in the Northern Hemisphere Stratospheric Polar Vortex Response to Climate Change

Journal of Climate ◽

10.1175/jcli-d-18-0041.1 ◽

2018 ◽

Vol 31 (16) ◽

pp. 6371-6391 ◽

Cited By ~ 17

Author(s):

Isla R Simpson ◽

Peter Hitchcock ◽

Richard Seager ◽

Yutian Wu ◽

Patrick Callaghan

Keyword(s):

Northern Hemisphere ◽

General Circulation ◽

Polar Vortex ◽

General Circulation Models ◽

Cmip5 Models ◽

Regression Analyses ◽

Wide Range ◽

Downward Influence

Abstract General circulation models display a wide range of future predicted changes in the Northern Hemisphere winter stratospheric polar vortex. The downward influence of this stratospheric uncertainty on the troposphere has previously been inferred from regression analyses across models and is thought to contribute to model spread in tropospheric circulation change. Here we complement such regression analyses with idealized experiments using one model where different changes in the zonal-mean stratospheric polar vortex are artificially imposed to mimic the extreme ends of polar vortex change simulated by models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The influence of the stratospheric vortex change on the tropospheric circulation in these experiments is quantitatively in agreement with the inferred downward influence from across-model regressions, indicating that such regressions depict a true downward influence of stratospheric vortex change on the troposphere below. With a relative weakening of the polar vortex comes a relative increase in Arctic sea level pressure (SLP), a decrease in zonal wind over the North Atlantic, drying over northern Europe, and wetting over southern Europe. The contribution of stratospheric vortex change to intermodel spread in these quantities is assessed in the CMIP5 models. The spread, as given by 4 times the across-model standard deviation, is reduced by roughly 10% on regressing out the contribution from stratospheric vortex change, while the difference between models on extreme ends of the distribution in terms of their stratospheric vortex change can reach up to 50% of the overall model spread for Arctic SLP and 20% of the overall spread in European precipitation.

The leading modes of NH extratropical tropopause variability and their connection with stratosphere-troposphere variability

Climate Dynamics ◽

10.1007/s00382-020-05595-7 ◽

2021 ◽

Author(s):

Jinju Kim ◽

Kwang-Yul Kim

Keyword(s):

Phase Fluctuation ◽

Polar Vortex ◽

Early Spring ◽

The Arctic ◽

Function Technique ◽

Two Phase ◽

Stratospheric Temperature ◽

Extratropical Tropopause

AbstractThe leading modes of Northern Hemisphere tropopause variability for November–April (1979/1980–2018/2019) and the associated stratosphere-troposphere variability were analyzed based on the NCEP and ERA interim reanalysis products. For this, cyclostationary empirical orthogonal function technique is employed. The first two modes feature the intraseasonal evolution of tropopause pressure anomalies over the Arctic, which respond directly to stratospheric temperature fluctuations in association with stratospheric polar vortex variations. These two modes reflect the link between stratospheric polar vortex strength and high-latitude tropospheric circulation. The first mode represents a single-phase fluctuation of the stratospheric polar vortex from winter to early spring. The second mode describes a two-phase fluctuation of the stratospheric vortex with opposite signs in winter and in spring. Tropopause pressure anomalies near the mid-latitude tropospheric jet regions exhibit significant zonal variation. In the first mode, in particular, these mid-latitude tropopause anomalies are linked to asymmetric jet variations in the Atlantic and the Pacific regions. In regard to the Northern Annular mode, distinct vertical evolution structures of the two modes are practically related to the varying evolutionary structure of extreme vortex events with relatively long persistence.

Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part IV: Planetary and Synoptic Wave-Breaking Processes during the NAO Life Cycle

Journal of the Atmospheric Sciences ◽

10.1175/2007jas2440.1 ◽

2008 ◽

Vol 65 (3) ◽

pp. 737-765 ◽

Cited By ~ 15

Author(s):

Dehai Luo ◽

Tingting Gong ◽

Yina Diao

Keyword(s):

Life Cycle ◽

Wave Breaking ◽

Planetary Wave ◽

Initial Conditions ◽

Low Frequency ◽

Phase Evolution ◽

Life Cycles ◽

Necessary Condition ◽

Mean Flow ◽

The North

Abstract Based on a highly idealized, analytical solution of the North Atlantic Oscillation (NAO) derived in Part III of this series, it is shown that wave breaking is not a necessary condition for the occurrence of NAO events. The breaking of synoptic waves can arise from the interaction between planetary and synoptic waves that gives rise to NAO events, and the type of wave breaking is dominated by the initial conditions of the two waves that determine the phase of the NAO. The planetary wave breaking (PWB) seems to be attributed to an amplification of the NAO amplitude. It is further found that both the planetary wave breaking and the cyclonic (anticyclonic) breaking of synoptic waves undergo an in-phase (out phase) evolution during the life cycles of negative (positive) phase NAO, or NAO− (NAO+), events. An interesting result found is that for NAO− (NAO+) events the breaking of synoptic waves is enhanced (weakened) during the growing phase, but is weakened (enhanced) during the decaying phase. In the absence of a topographic planetary wave (TPW), PWB occurs mainly in the midlatitude regions of the Atlantic basin for NAO− events, but is concentrated in subtropical and subpolar regions for NAO+ events. However, once the TPW is involved, the reversed planetary-scale potential vorticity (PV) gradient that characterizes the PWB exhibits a southwest–northeast (southeast–northwest) tilted tripole for NAO− (NAO+) events, in agreement with the diagnostic results presented herein. The PWB in the subtropical Atlantic is found to occur more frequently for NAO+ events than for NAO− events because the weaker subtropical mean flow is more likely to emerge during the NAO+ life cycle. In conclusion, the results of the highly idealized model used here appear to show that the PWB, synoptic wave breaking, and meridional shift of the westerly jet may be different descriptions of the NAO phenomenon.