Regime Behavior in the Upper Stratosphere as a Precursor of Stratosphere-Troposphere Coupling in the Northern Winter

AbstractA new regime index is constructed to capture the seasonal development of the stratospheric polar vortex in the northern winter, based on the standard deviation of Ertel’s potential vorticity in the upper stratosphere in November-December. The narrow-jet flow regime is characterized by a polar vortex that is more confined to high latitudes in the early winter upper stratosphere. This upper-level vortex configuration is more susceptible to the disturbances of upward propagating planetary-scale Rossby waves; the stratospheric polar vortex thus weakens earlier and is vertically shallower. The wide-jet flow regime is characterized by a broader-than-average polar vortex that extends further into the subtropics in the early-winter upper stratosphere. The polar night jet then gradually strengthens, moves poleward and penetrates deep into the lowermost stratosphere, with a sharply-defined polar vortex edge accompanied due to more frequent Rossby wave breaking.Composite differences analyses show that the wide and narrow jet regimes, defined in the uppermost stratosphere in November-December, lead to different circulation anomalies of the lower-stratosphere and the troposphere in January-February, offering the potential for improved predictability of sub-seasonal to seasonal forecasts up to two months ahead. The lower tropospheric responses in January-February are zonally asymmetric. The narrow-jet regime projects most strongly over the North Atlantic, with an equatorward-shifted, and/or broader mid-latitude westerly jet. The wide-jet-regime response is characterized by a weakened mid-latitude westerly jet over the North Pacific. The two flow regimes also differ in their impacts on the storm track over Western Europe and the east coast of America, which may have implications for extreme weather events in those regions.

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Surface impacts of the Quasi Biennial Oscillation

10.5194/acp-2017-1065 ◽

2017 ◽

Author(s):

Lesley J. Gray ◽

James A. Anstey ◽

Yoshio Kawatani ◽

Hua Lu ◽

Scott Osprey ◽

...

Keyword(s):

North Pacific ◽

Polar Vortex ◽

Late Winter ◽

Early Winter ◽

Quasi Biennial Oscillation ◽

Stratospheric Polar Vortex ◽

Tropical Precipitation ◽

The North ◽

Biennial Oscillation ◽

The North Pacific

Abstract. Teleconnections between the Quasi Biennial Oscillation (QBO) and the Northern Hemisphere zonally-averaged zonal winds, mean sea level pressure (mslp) and tropical precipitation are explored using regression analysis. A novel technique is introduced to separate responses associated with the stratospheric polar vortex from other underlying mechanisms. A previously reported mslp response in January, with a pattern that resembles the positive phase of the North Atlantic Oscillation (NAO) under QBO westerly conditions, is confirmed and found to be primarily associated with a QBO modulation of the stratospheric polar vortex. This mid-winter response is relatively insensitive to the exact height of the maximum QBO westerlies and a maximum response occurs with westerlies over a relatively deep range between 10–70 hPa. Two additional mslp responses are reported, in early winter (December) and late winter (February/March). In contrast to the January response the early and late winter responses show maximum sensitivity to the QBO winds at ~ 20 hPa and ~ 70 hPa but are relatively insensitive to the QBO winds in between (~ 50 hPa). The late winter response is centred over the North Pacific and is associated with QBO influence from the lowermost stratosphere at tropical/subtropical latitudes. The early winter response consists of anomalies over both the North Pacific and Europe, but the mechanism is unclear and requires further investigation. QBO anomalies are found in tropical precipitation amounts and a southward shift of the Inter-tropical Convergence Zone under westerly QBO conditions is also evident.

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Impact of the Quasi-Biennial Oscillation on the Northern Winter Stratospheric Polar Vortex in CMIP5/6 Models

Journal of Climate ◽

10.1175/jcli-d-19-0663.1 ◽

2020 ◽

Vol 33 (11) ◽

pp. 4787-4813 ◽

Cited By ~ 4

Author(s):

Jian Rao ◽

Chaim I. Garfinkel ◽

Ian P. White

Keyword(s):

Polar Vortex ◽

The Arctic ◽

Early Winter ◽

Flux Divergence ◽

Quasi Biennial Oscillation ◽

Stratospheric Polar Vortex ◽

Northern Winter ◽

P Flux ◽

The Impact ◽

Biennial Oscillation

AbstractUsing 16 CMIP5/6 models with a spontaneously generated quasi-biennial oscillation (QBO)-like phenomenon, this study investigates the impact of the QBO on the northern winter stratosphere. Eight of the models simulate a QBO with a period similar to that observed (25–31 months), with other models simulating a QBO period of 20–40 months. Regardless of biases in QBO periodicity, the Holton–Tan relationship can be well simulated in CMIP5/6 models with more planetary wave convergence in the polar stratosphere in easterly QBO winters. This wave polar convergence occurs not only due to the Holton–Tan mechanism, but also in the midlatitude upper stratosphere where an Elissen–Palm (E-P) flux divergence dipole (with poleward E-P flux) is simulated in most models. The wave response in the upper stratosphere appears related to changes in the background circulation through a directly excited meridional–vertical circulation cell above the maximum tropical QBO easterly center. The midlatitude upwelling in this anticlockwise cell is split into two branches, and the north branch descends in the Arctic region and warms the stratospheric polar vortex. Most models underestimate the Arctic stratospheric warming in early winter during easterly QBO. Further analysis suggests that this bias is not due to an overly weak response to a given QBO phase, as the models simulate a realistic response if one focuses on similar QBO phases. Rather, the model bias is due to the too-low frequency of strong QBO winds in the lower stratosphere in early winter simulated by the models.

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Planetary Wave Breaking and Tropospheric Forcing as Seen in the Stratospheric Sudden Warming of 2006

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2784.1 ◽

2009 ◽

Vol 66 (2) ◽

pp. 495-507 ◽

Cited By ~ 53

Author(s):

Lawrence Coy ◽

Stephen Eckermann ◽

Karl Hoppel

Keyword(s):

North Atlantic ◽

Wave Breaking ◽

Potential Temperature ◽

Polar Vortex ◽

Stratospheric Polar Vortex ◽

Stratospheric Sudden Warming ◽

Advanced Level ◽

Earth Observing System ◽

The North ◽

Temperature Surface

Abstract The major stratospheric sudden warming (SSW) of January 2006 is examined using meteorological fields from Goddard Earth Observing System version 4 (GEOS-4) analyses and forecast fields from the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics, High Altitude (NOGAPS-ALPHA). The study focuses on the upper tropospheric forcing that led to the major SSW and the vertical structure of the subtropic wave breaking near 10 hPa that moved low tropical values of potential vorticity (PV) to the pole. Results show that an eastward-propagating upper tropospheric ridge over the North Atlantic with its associated cold temperature perturbations (as manifested by high 360-K potential temperature surface perturbations) and large positive local values of meridional heat flux directly forced a change in the stratospheric polar vortex, leading to the stratospheric subtropical wave breaking and warming. Results also show that the anticyclonic development, initiated by the subtropical wave breaking and associated with the poleward advection of the low PV values, occurred over a limited altitude range of approximately 6–10 km. The authors also show that the poleward advection of this localized low-PV anomaly was associated with changes in the Eliassen–Palm (EP) flux from equatorward to poleward, suggesting an important role for Rossby wave reflection in the SSW of January 2006. Similar upper tropospheric forcing and subtropical wave breaking were found to occur prior to the major SSW of January 2003.

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The Influence of the Quasi-Biennial Oscillation on the Troposphere in Winter in a Hierarchy of Models. Part I: Simplified Dry GCMs

Journal of the Atmospheric Sciences ◽

10.1175/2011jas3665.1 ◽

2011 ◽

Vol 68 (6) ◽

pp. 1273-1289 ◽

Cited By ~ 50

Author(s):

Chaim I. Garfinkel ◽

Dennis L. Hartmann

Keyword(s):

Zonal Wind ◽

Climate Model ◽

Polar Vortex ◽

Equation Model ◽

Quasi Biennial Oscillation ◽

Stratospheric Polar Vortex ◽

The North ◽

Subtropical Jet ◽

Long Time ◽

Biennial Oscillation

Abstract A dry primitive equation model is used to explain how the quasi-biennial oscillation (QBO) of the tropical stratosphere can influence the troposphere, even in the absence of tropical convection anomalies and a variable stratospheric polar vortex. QBO momentum anomalies induce a meridional circulation to maintain thermal wind balance. This circulation includes zonal wind anomalies that extend from the equatorial stratosphere into the subtropical troposphere. In the presence of extratropical eddies, the zonal wind anomalies are intensified and extend downward to the surface. The tropospheric response differs qualitatively between integrations in which the subtropical jet is strong and integrations in which the subtropical jet is weak. While fluctuation–dissipation theory provides a guide to predicting the response in some cases, significant nonlinearity in others, particularly those designed to model the midwinter subtropical jet of the North Pacific, prevents its universal application. When the extratropical circulation is made zonally asymmetric, the response to the QBO is greatest in the exit region of the subtropical jet. The dry model is able to simulate much of the Northern Hemisphere wintertime tropospheric response to the QBO observed in reanalysis datasets and in long time integrations of the Whole Atmosphere Community Climate Model (WACCM).

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Combined Impact of El Niño–Southern Oscillation and Pacific Decadal Oscillation on the Northern Winter Stratosphere

Atmosphere ◽

10.3390/atmos10040211 ◽

2019 ◽

Vol 10 (4) ◽

pp. 211 ◽

Cited By ~ 5

Author(s):

Jian Rao ◽

Rongcai Ren ◽

Xin Xia ◽

Chunhua Shi ◽

Dong Guo

Keyword(s):

El Niño ◽

North Pacific ◽

El Nino ◽

Southern Oscillation ◽

Polar Vortex ◽

La Niña ◽

Stratospheric Polar Vortex ◽

The North ◽

La Nina ◽

Sst Anomalies

Using reanalysis and the sea surface temperature (SST) analysis, the combined impact of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on the northern winter stratosphere is investigated. The warm and weak stratospheric polar vortex response to El Niño simply appears during positive PDO, whereas the cold and strong stratospheric polar vortex response to La Niña is preferable during negative PDO in the reanalysis. Two mechanisms may account for the enhanced stratospheric response when ENSO and PDO are in phase. First, the asymmetries of the intensity and frequency between El Niño and La Niña can be identified for the two PDO phases. Second, the extratropical SST anomalies in the North Pacific may also play a role in the varying extratropical response to ENSO. The North Pacific SST anomalies related to PDO superimpose ENSO SST anomalies when they are in phase but undermine them when they are out of phase. The superimposed North Pacific SST anomalies help to increase SST meridional gradient anomalies between tropical and extratropics, as well as to lock the local height response to ENSO. Therefore, the passages for the upward propagation of waves from the troposphere is more unimpeded when positive PDO is configured with El Niño, and vice versa when negative PDO is configured with La Niña.

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Influence of Wintertime Polar Vortex Variation on the Climate over the North Pacific during Late Winter and Spring

Atmosphere ◽

10.3390/atmos10110670 ◽

2019 ◽

Vol 10 (11) ◽

pp. 670 ◽

Cited By ~ 3

Author(s):

Kequan Zhang ◽

Tao Wang ◽

Mian Xu ◽

Jiankai Zhang

Keyword(s):

Pacific Ocean ◽

North Pacific ◽

Geopotential Height ◽

North Pacific Ocean ◽

Polar Vortex ◽

Late Winter ◽

Stratospheric Polar Vortex ◽

The North ◽

The North Pacific ◽

The Bering Sea

The effects of wintertime stratospheric polar vortex variation on the climate over the North Pacific Ocean during late winter and spring are analyzed using the National Centers for Environmental Predictions, version 2 (NCEP2) reanalysis dataset. The analysis revealed that, during weak polar vortex (WPV) events, there are noticeably lower geopotential height anomalies over the Bering Sea and greater height anomalies over the central part of the North Pacific Ocean than during strong polar vortex (SPV) events. The formation of the dipolar structure of the geopotential height anomalies is due to a weakened polar jet and a strengthened mid-latitude jet in the troposphere via geostrophic equilibrium. The mechanisms responsible for the changes in the tropospheric jet over the North Pacific Ocean are summarized as follows: when the stratospheric polar westerly is decelerated, the high-latitude eastward waves slow down, and the enhanced equatorward propagation of the eddy momentum flux throughout the troposphere at 60° N. Consequently, the eddy-driven jet over the North Pacific Ocean also shows a southward displacement, leading to a weaker polar jet but a stronger mid-latitude westerly compared with those during the SPV events. Furthermore, anomalous anti-cyclonic flows associated with the higher pressure over the North Pacific Ocean during WPV events induce a warming sea surface temperature (SST) over the western and central parts of the North Pacific Ocean and a cooling SST over the Bering Sea and along the west coast of North America. This SST pattern can last until May, which favors the persistence of the anti-cyclonic flows over the North Pacific Ocean during WPV events. A well-resolved stratosphere and coupled atmosphere-ocean model (CMCC-CMS) can basically reproduce the impacts of stratospheric polar vortex variations on the North Pacific climate as seen in NCEP2 data, although the simulated dipole of geopotential height anomalies is shifted more southward.

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More-Persistent Weak Stratospheric Polar Vortex States Linked to Cold Extremes

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-16-0259.1 ◽

2018 ◽

Vol 99 (1) ◽

pp. 49-60 ◽

Cited By ~ 74

Author(s):

Marlene Kretschmer ◽

Dim Coumou ◽

Laurie Agel ◽

Mathew Barlow ◽

Eli Tziperman ◽

...

Keyword(s):

Southern Oscillation ◽

Polar Vortex ◽

Late Winter ◽

Boreal Winter ◽

Arctic Amplification ◽

Stratospheric Polar Vortex ◽

Large Variability ◽

Vortex States ◽

Westerly Jet ◽

Cold Extremes

Abstract 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.

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Topographic forcing from East Asia and North America in the northern winter stratosphere and their mutual interference

10.5194/egusphere-egu2020-1392 ◽

2020 ◽

Author(s):

Rongcai Ren ◽

Xin Xia ◽

Jian Rao

Keyword(s):

North America ◽

East Asia ◽

Climate Model ◽

Polar Vortex ◽

Wave Pattern ◽

Mutual Interference ◽

Mean Flow ◽

Stratospheric Polar Vortex ◽

Northern Winter ◽

Topographic Forcing

This study uses the stratosphere-resolved Whole Atmosphere Community Climate Model to demonstrate the &#8220;independent&#8221; and &#8220;dependent&#8221; topographic forcing from the topography of East Asia (EA) and North American (NA), and their &#8220;joint&#8221; forcing in the northern winter stratosphere. The mutual interference between the EA and NA forcing is also demonstrated. Specifically, without EA, an independent NA can also, like EA, induce a severe polar warming and weakening of the stratospheric polar vortex. While EA favors a displacement of the polar vortex toward Eurasia, NA favors a displacement toward the North America&#8211;Atlantic region. However, the independent-EA-forced weakening effect on the polar vortex can be largely decreased and changes to a location displacement when NA exists, and the interference the other way around is even more critical, being able to completely offset the independent-NA-forced effect, because EA can substantively obstruct NA&#8217;s effect on the tropospheric wave pattern over the Eurasia&#8211;Pacific region. The much stronger/weaker interference of EA/NA is associated with its stronger/weaker downstream weakening effect on the zonal flow that impinges on NA/EA. The mutual interference always tends to further destruct the upward wave fluxes over the eastern North Pacific and enhance the downward wave fluxes over NA. The overall changes in upward wave fluxes, as well as that in the Rossby stationary wavenumber responsible for the stratospheric changes, are related to changes in the zonal-mean flow pattern. The joint effects of EA and NA, rather than being a linear superimposition of their independent effects, are largely dominated by the effects of EA.

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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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