scholarly journals Synoptic–Dynamic Climatology of the Aleutian High

2018 ◽  
Vol 75 (4) ◽  
pp. 1271-1283 ◽  
Author(s):  
Stephen J. Colucci ◽  
Thomas S. Ehrmann
Keyword(s):  
Wave Breaking ◽  
Geopotential Height ◽  
Polar Vortex ◽  
Heat Fluxes ◽  
Aleutian Islands ◽  
Height Anomaly ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Geometric Moments ◽  
Almost All

Abstract A climatology of the anticyclone that commonly appears over the Aleutian Islands in the wintertime Northern Hemisphere stratosphere is presented. Applying a geometric moments technique to a reanalysis dataset and updating a previously published definition, 68 Aleutian high (AH) events have been identified during 35 winter (October–March) seasons (1979/80–2013/14), or about 2 events per season. The events lasted an average of approximately 33 days. Thirteen of the 68 AH events each temporally and spatially coincided with tropospheric blocking identified with a wave-breaking definition, while 41 of the AH onsets each coincided with a persistently positive geopotential height anomaly in the troposphere. Also, 41 of the 68 AH events each coincided with or were followed by an objectively defined disturbance (split or displacement) to the stratospheric polar vortex. Finally, 47 of these disturbance events were each preceded by an AH onset, such that in almost all winters (33 out of 35), an early season AH was followed by a later-season polar vortex disturbance (PVD). Potential vorticity (PV) inversion revealed that the geopotential height rises associated with composite AH onset were forced primarily by anticyclonic PV increases in the stratosphere, with the troposphere providing a lesser contribution. Poleward eddy heat fluxes in the stratosphere preceded and especially followed composite AH onset, consistent with the findings that composite AH onset was forced primarily by anticyclonic PV increases in the stratosphere and that many AH onsets were each followed by a PVD onset.

scholarly journals Diagnostic Comparison of Tropospheric Blocking Events with and without Sudden Stratospheric Warming

2015 ◽  
Vol 72 (6) ◽  
pp. 2227-2240 ◽  
Author(s):  
Stephen J. Colucci ◽  
Michael E. Kelleher
Keyword(s):  
Geopotential Height ◽  
Onset Time ◽  
Polar Vortex ◽  
Outer Edge ◽  
Heat Fluxes ◽  
Necessary Condition ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Polar Vortex ◽  
Upper Troposphere

Abstract Tropospheric blocking events over the Northern Hemisphere during 1980–2012 were composited and contrasted according to whether they coincided in time with a sudden stratospheric warming (SSW). Those that coincided with an SSW were associated with significantly greater poleward eddy heat fluxes in the upper troposphere near the block onset time than were those blocking events not coinciding with an SSW. Furthermore, the heat fluxes in the SSW–blocking composites were concentrated inside the stratospheric polar vortex (i.e., within an area enclosed by the outer edge of an objectively defined polar vortex). Thermally forced stratospheric geopotential height rises were also significantly larger near block onset time inside the stratospheric polar vortex in the SSW–blocking composites than in the non-SSW–blocking cases. Although all the SSW events during the investigated period coincided with tropospheric blocking, the reverse was not true since there were many more blocking events than SSWs. Therefore, blocking itself was not a sufficient condition for an SSW. It is conjectured that blocking may not be a necessary condition for an SSW if persistently anomalous tropospheric heat fluxes and thermally forced, stratospheric geopotential height rises, concentrated inside the stratospheric vortex, occur in the absence of blocking.

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

2009 ◽  
Vol 66 (2) ◽  
pp. 495-507 ◽  
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.

scholarly journals Quantifying Asymmetric Wave Breaking and Two-Way Transport

2004 ◽  
Vol 61 (22) ◽  
pp. 2735-2748 ◽  
Author(s):  
Noboru Nakamura
Keyword(s):  
Wave Breaking ◽  
Polar Vortex ◽  
Effective Diffusivity ◽  
The Other ◽  
Stratospheric Polar Vortex ◽  
Air Masses ◽  
Rossby Wave Breaking ◽  
Advection Diffusion Equation ◽  
Extratropical Tropopause ◽  
Asymmetric Wave

Abstract Effective diffusivity calculated from a scalar field that obeys the advection–diffusion equation has proved useful for estimating the permeability of unsteady boundaries of air masses such as the edge of the stratospheric polar vortex and the extratropical tropopause. However, the method does not discriminate the direction of transport—whereas some material crosses the boundary from one side to the other, some material does so in the other direction—yet the extant method concerns only the net transport. In this paper, the diagnostic is extended to allow partitioning of fluxes of mass and tracer into opposing directions. This is accomplished by discriminating the regions of “inward” and “outward” wave breaking with the local curvature of the tracer field. The utility of the new method is demonstrated for nonlinear Kelvin– Helmholtz instability and Rossby wave breaking in the stratosphere using a numerically generated tracer. The method successfully quantifies two-way transport and hence the direction of wave breaking—the predominantly equatorward breaking of Rossby waves in the extratropical middle stratosphere, for example. Isolated episodes of mixing are identified well, particularly by the mass flux that primarily arises from the tracer filaments. Comparison of different transport schemes suggests that the results are reasonably robust under a varying subgrid representation of the model.

Stratospheric mountain waves trailing across northern Europe

2021 ◽  
Author(s):  
Andreas Dörnbrack
Keyword(s):  
Gravity Waves ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
Polar Front ◽  
Northern Europe ◽  
Polar Night ◽  
Stratospheric Polar Vortex ◽  
Mountain Waves ◽  
Almost All

<table><tbody><tr><td> <p><span>Planetary waves disturbed the hitherto stable Arctic stratospheric polar vortex mid of<br>January 2016 in such a way that unique tropospheric and stratospheric flow conditions<br>for vertically and horizontally propagating mountain waves developed. Co-existing<br>strong low-level westerly winds across almost all European mountain ranges plus the<br>almost zonally-aligned polar front jet created these favorable conditions for deeply<br>propagating gravity waves. Furthermore, the northward displacement of the polar night<br>jet resulted in a wide-spread coverage of stratospheric mountain waves trailling across<br>northern Europe. This paper describes the particular meteorological setting by<br>analyzing the tropospheric and stratospheric flows based on the ERA5 data. The<br>potential of the flow for exciting internal gravity waves from non-orographic sources is<br>evaluated across all altitudes by considering various instability indices as δ , Ro, Ro ζ , Ro<sub>⊥</sub> ,<br>and Δ NBE</span><span>. </span></p> <p><span>The analyzed gravity waves are described and characterized in terms of<br>commonly used parameters. The main finding of this case study is the exceptionally<br>vast extension of the mountain waves trailing to high latitudes originating from the flow<br>across the mountainous sources that are located at about 45 N. As a useful addition to<br>the case study, tracks for potential research flights are proposed that sample the<br>waves by a vertically pointing airborne remote-sensing instrument. Benefits and<br>drawbacks of the different approaches to observe the meridional focussing of the<br>mountain waves into the polar night jet are discussed.</span></p> </td> </tr></tbody></table><p> </p>

scholarly journals Eurasian Cold Air Outbreaks under Different Arctic Stratospheric Polar Vortex Strengths

2019 ◽  
Vol 76 (5) ◽  
pp. 1245-1264 ◽  
Author(s):  
Jinlong Huang ◽  
Wenshou Tian
Keyword(s):  
Climate Models ◽  
Sensible Heat Flux ◽  
Coupled Model ◽  
Surface Air Temperature ◽  
Polar Vortex ◽  
Northern Eurasia ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Cold Air ◽  
Cold Air Outbreaks

Abstract This study analyzes the differences and similarities of Eurasian cold air outbreaks (CAOs) under the weak (CAOW), strong (CAOS), and neutral (CAON) stratospheric polar vortex states and examines the potential links between the polar vortex and Eurasian CAOs. The results indicate that the colder surface air temperature (SAT) over Europe in the earlier stages of CAOW events is likely because the amplitude of the preexisting negative North Atlantic Oscillation pattern is larger in CAOW events than in CAON and CAOS events. Marked by the considerably negative stratospheric Arctic Oscillation signals entering the troposphere, the SAT at midlatitudes over eastern Eurasia in CAOW events is colder than in CAON events. A larger diabatic heating rate related to a positive sensible heat flux anomaly in CAOW events likely offsets, to some degree, the cooling effect caused by the stronger cold advection and makes the differences in area-averaged SAT anomalies over northern Eurasia between the CAOW and CAON events look insignificant in most stages. Massive anomalous waves from the low-latitude western Pacific merge over northeastern Eurasia, then weaken the westerly wind over this region to create favorable conditions for southward advection of cold air masses in the earlier stages of all three types of CAOs. This study further analyzes the interannual relationship between the stratospheric polar vortex strength and the intensity of Eurasian CAOs and finds that climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) relative to the reanalysis dataset tend to underestimate the correlation between them. The relationship between them is strengthening under representative concentration pathway 4.5 (RCP4.5) and 8.5 (RCP8.5) scenarios over the period 2006–60. In addition, the intensity of Eurasian CAOs exhibits a decreasing trend in the past and in the future.

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

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 670 ◽  
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.

scholarly journals Stratospheric influence on North Atlantic marine cold air outbreaks following sudden stratospheric warming events

2020 ◽  
Vol 1 (2) ◽  
pp. 541-553
Author(s):  
Hilla Afargan-Gerstman ◽  
Iuliia Polkova ◽  
Lukas Papritz ◽  
Paolo Ruggieri ◽  
Martin P. King ◽  
...  
Keyword(s):  
North Atlantic ◽  
Geopotential Height ◽  
Barents Sea ◽  
Height Anomaly ◽  
Labrador Sea ◽  
Stratospheric Polar Vortex ◽  
Cold Air ◽  
The North ◽  
The North Atlantic ◽  
Cold Air Outbreaks

Abstract. Marine cold air outbreaks (MCAOs) in the northeastern North Atlantic occur due to the advection of extremely cold air over an ice-free ocean. MCAOs are associated with a range of severe weather phenomena, such as polar lows, strong surface winds and intense cooling of the ocean surface. Given these extreme impacts, the identification of precursors of MCAOs is crucial for improved long-range prediction of associated impacts on Arctic infrastructure and human lives. MCAO frequency has been linked to the strength of the stratospheric polar vortex, but the study of connections to the occurrence of extreme stratospheric events, known as sudden stratospheric warmings (SSWs), has been limited to cold extremes over land. Here, the influence of SSW events on MCAOs over the North Atlantic ocean is studied using reanalysis datasets. Overall, SSW events are found to be associated with more frequent MCAOs in the Barents Sea and the Norwegian Sea compared to climatology and less frequent MCAOs in the Labrador Sea. In particular, SSW events project onto an anomalous dipole pattern of geopotential height 500 hPa, which consists of a ridge anomaly over Greenland and a trough anomaly over Scandinavia. By affecting the variability of the large-scale circulation patterns in the North Atlantic, SSW events contribute to the strong northerly flow over the Barents and Norwegian seas and thereby increase the likelihood of MCAOs in these regions. In contrast, the positive geopotential height anomaly over Greenland reduces the probability of MCAOs in the Labrador Sea after SSW events. As SSW events tend to have a long-term influence on surface weather, these results are expected to benefit the predictability of MCAOs in the Nordic Seas for winters with SSW events.

Exploring the Tropospheric Response to Stratospheric Variability Using Lagged Quantile Regression

2021 ◽  
Author(s):  
Kathrin Finke ◽  
Abdel Hannachi
Keyword(s):  
Quantile Regression ◽  
Conditional Distribution ◽  
Polar Vortex ◽  
Supplementary Information ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Response Variable ◽  
Tropospheric Circulation ◽  
The Impact ◽  
Stratospheric Variability

<p>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,  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.</p>

The Impact of the Stratospheric Polar Vortex Shift on the Arctic Oscillation

2021 ◽  
Vol 34 (10) ◽  
pp. 4129-4143
Author(s):  
Yongjia Lu ◽  
Wenshou Tian ◽  
Jiankai Zhang ◽  
Jinlong Huang ◽  
Ruhua Zhang ◽  
...  
Keyword(s):  
Arctic Oscillation ◽  
Polar Vortex ◽  
The Arctic ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Eurasian Continent ◽  
Time Period ◽  
Action Center ◽  
The Arctic Oscillation ◽  
The Impact

AbstractUsing the ERA-Interim reanalysis dataset for the time period 1979–2016, we analyzed the influence of the stratospheric polar vortex shift on the Arctic Oscillation (AO) in winter (December–March). The results show that a shift in the stratospheric polar vortex toward the Eurasian continent is favorable for the occurrence of the negative phase of the AO. The duration of the AO events accompanied by the stratospheric polar vortex shift toward the Eurasian continent (AO-shift events) is longer than that of the remaining negative AO events (AO-noshift events), and the intensity of AO-shift events is greater than that of AO-noshift events from day 4 to day 15 of the life cycle of the events. The enhancement in the AO intensity during AO-shift events is likely due to downward extension of the stratospheric northern annular mode (NAM) signals and more poleward-propagating planetary waves in the troposphere and lower stratosphere and their convergence in the mid-high latitudes. Furthermore, the polar vortex shift can lead to changes in the intensity of the three action centers in the AO spatial pattern at 500 hPa. In general, during AO-shift events, the three action centers are stronger than those during AO-noshift events. There is an overall westward shift of the Arctic action center during AO-shift events, which may be closely related to the changes of Greenland blocking frequency.

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