scholarly journals Preconditioning of Arctic Stratospheric Polar Vortex Shift Events

2018 ◽  
Vol 31 (14) ◽  
pp. 5417-5436 ◽  
Author(s):  
Jinlong Huang ◽  
Wenshou Tian ◽  
Lesley J. Gray ◽  
Jiankai Zhang ◽  
Yan Li ◽  
...  
Keyword(s):  
North America ◽  
North Atlantic ◽  
Planetary Wave ◽  
Polar Vortex ◽  
The Arctic ◽  
Bering Strait ◽  
Surface Cooling ◽  
Stratospheric Polar Vortex ◽  
Significant Difference ◽  
Eastern North Atlantic

Abstract This study examines the preconditioning of events in which the Arctic stratospheric polar vortex shifts toward Eurasia (EUR events), North America (NA events), and the Atlantic (ATL events) using composite analysis. An increase in blocking days over northern Europe and a decrease in blocking days over the Bering Strait favor the movement of the vortex toward Eurasia, while the opposite changes in blocking days over those regions favor the movement of the vortex toward North America. An increase in blocking days over the eastern North Atlantic and a decrease in blocking days over the Bering Strait are conducive to movement of the stratospheric polar vortex toward the Atlantic. These anomalous precursor blocking patterns are interpreted in terms of the anomalous zonal wave-1 or wave-2 planetary wave fluxes into the stratosphere that are known to influence the vortex position and strength. In addition, the polar vortex shift events are further classified into events with small and large polar vortex deformation, since the two types of events are likely to have a different impact at the surface. A significant difference in the zonal wave-2 heat flux into the lower stratosphere exists prior to the two types of events and this is linked to anomalous blocking patterns. This study further defines three types of tropospheric blocking events in which the spatial patterns of blocking frequency anomalies are similar to the blocking patterns prior to EUR, NA, and ATL events, respectively, and our reanalysis reveals that the polar vortex is indeed more likely to shift toward Eurasia, North America, and the Atlantic in the presence of the above three defined tropospheric blocking events. These shifts of the polar vortex toward Eurasia, North America, and the Atlantic lead to statistically significant negative height anomalies near the tropopause and corresponding surface cooling anomalies over these three regions.

Understanding the role of the troposphere in the surface impact of the 2018 sudden stratospheric warming event

2021 ◽  
Author(s):  
Juan J. González-Alemán ◽  
Christian M. Grams ◽  
Blanca Ayarzagüena ◽  
Pablo Zurita-Gotor ◽  
Daniela I. V. Domeisen Domeisen ◽  
...  
Keyword(s):  
North Atlantic ◽  
Vortex Breakdown ◽  
Rapid Change ◽  
Polar Vortex ◽  
The Arctic ◽  
Lead Times ◽  
Strong Impact ◽  
Ensemble Forecasts ◽  
Stratospheric Polar Vortex ◽  
The North

<p>Sudden stratospheric warmings (SSWs) are impressive phenomena that consist of a rapid stratospheric polar vortex breakdown. SSWs can have a strong impact on the tropospheric weather and are mainly associated with the negative phases of the Arctic and North Atlantic Oscillations (AO, NAO), and with northern European cold outbreaks, thus causing high societal impact. However, the mechanisms behind the downward impact from the stratosphere are insufficiently understood, especially the role played by the troposphere. In this work, we investigate this coupling and its associated predictability limits by studying the 2018 SSW event.</p><p>By analyzing ECMWF 15-day ensemble forecasts and partitioning them into different weather regimes, we search for possible dynamical tropospheric events that may have favored the downward stratosphere-troposphere coupling during and after the SSW. It is found that two cyclogenesis events were the main drivers of the negative NAO pattern associated with a Greenland Blocking, causing a rapid change from prevailing westerlies into a blocked state in the North Atlantic region. Unless these cyclogenesis events are simulated in the forecasts, the prediction of a Greenland Blocking does not become highly prevalent. No important stratospheric differences between WRs were found. A possible oceanic contribution to this blocked state is also found. This work corroborates that individual synoptic events might constitute a “predictability barrier" for subsequent forecast lead times. It also sheds light, on the specific topic of troposphere-stratosphere coupling.</p>

scholarly journals Using Bayesian Networks to investigate the influence of subseasonal Arctic variability on midlatitude North Atlantic circulation

2020 ◽  
pp. 1-46
Author(s):  
Nathanael Harwood ◽  
Richard Hall ◽  
Giorgia Di Capua ◽  
Andrew Russell ◽  
Allan Tucker
Keyword(s):  
Bayesian Networks ◽  
North Atlantic ◽  
Hidden Variables ◽  
Polar Vortex ◽  
The Arctic ◽  
Stratospheric Polar Vortex ◽  
Arctic Warming ◽  
The North ◽  
The North Atlantic

AbstractRecent enhanced warming and sea ice depletion in the Arctic have been put forward as potential drivers of severe weather in the midlatitudes. Evidence of a link between Arctic warming and midlatitude atmospheric circulation is growing, but the role of Arctic processes relative to other drivers remains unknown. Arctic-midlatitude connections in the North Atlantic region are particularly complex but important due to the frequent occurrence of severe winters in recent decades. Here, Dynamic Bayesian Networks with hidden variables are introduced to the field to assess their suitability for teleconnection analyses. Climate networks are constructed to analyse North Atlantic circulation variability at 5-day to monthly timescales during the winter months of the years 1981-2018. The inclusion of a number of Arctic, midlatitude and tropical variables allows for an investigation into the relative role of Arctic influence compared to internal atmospheric variability and other remote drivers.A robust covariability between regions of amplified Arctic warming and two definitions of midlatitude circulation is found to occur entirely within winter at submonthly timescales. Hidden variables incorporated in networks represent two distinct modes of stratospheric polar vortex variability, capturing a periodic shift between average conditions and slower anomalous flow. The influence of the Barents-Kara Seas region on the North Atlantic Oscillation is found to be the strongest link at 5- and 10-day averages, whilst the stratospheric polar vortex strongly influences jet variability on monthly timescales.

scholarly journals Subseasonal Forecast Skill over the Northern Polar Region in Boreal Winter

2020 ◽  
Vol 33 (5) ◽  
pp. 1935-1951 ◽  
Author(s):  
Hai Lin
Keyword(s):  
Polar Region ◽  
Polar Vortex ◽  
Arctic Region ◽  
Seasonal Prediction ◽  
Forecast Skill ◽  
The Arctic ◽  
Boreal Winter ◽  
Bering Strait ◽  
Stratospheric Polar Vortex ◽  
The Arctic Oscillation

AbstractPentad (5-day averaged) forecast skill over the Arctic region in boreal winter is evaluated for the subseasonal to seasonal prediction (S2S) systems from three operational centers: the European Centre for Medium-Range Weather Forecasts (ECMWF), the U.S. National Centers for Environmental Prediction (NCEP), and Environment and Climate Change Canada (ECCC). The results indicate that for a lead time longer than about 10 days the forecast skill of 2-m air temperature and 500-hPa geopotential height in the Arctic area is low compared to the tropical and midlatitude regions. The three S2S systems have comparable forecast skill in the northern polar region. Relatively high skill is observed in the Arctic sector north of the Bering Strait in pentads 4–6. Possible sources of S2S predictability in the polar region are explored. The polar forecast skill is found to be dependent on the phase of the Arctic Oscillation (AO) in the initial condition; that is, forecasts initialized with the negative AO are more skillful than those starting from the positive AO. This is likely due to the influence of the stratospheric polar vortex. The tropical MJO is found to also influence the prediction skill in the polar region. Forecasts starting from MJO phases 6–7, which correspond to suppressed convection in the equatorial eastern Indian Ocean and enhanced convection in the tropical western Pacific, tend to be more skillful than those initialized from other MJO phases. To improve the polar prediction on the subseasonal time scale, it is important to have a well-represented stratosphere and tropical MJO and their associated teleconnections in the model.

Stratospheric modulation of cold air outbreaks and winter storms in the North Atlantic region and impacts on predictability

2021 ◽  
Author(s):  
Hilla Afargan-Gerstman ◽  
Iuliia Polkova ◽  
Lukas Papritz ◽  
Paolo Ruggieri ◽  
Martin P. King ◽  
...  
Keyword(s):  
North Atlantic ◽  
Storm Track ◽  
Polar Vortex ◽  
The Arctic ◽  
Damage Potential ◽  
Stratospheric Polar Vortex ◽  
Winter Storms ◽  
Cold Air ◽  
The North ◽  
Cold Air Outbreaks

<div> <p>Variability of the stratospheric polar vortex has the potential to influence surface weather by imposing negative North Atlantic Oscillation (NAO) conditions, associated with cold air outbreaks in the Arctic and a southward shift of the extratropical storm track. In particular, the likelihood of cold temperature extremes over the ocean, known as marine cold air outbreaks (MCAOs), have been associated with a range of hazardous conditions, including strong surface winds and the occurrence of extreme cyclones known as Polar Lows (PLs), posing risks for Arctic marine activity and infrastructure. Likewise, winter storms can lead to high damage potential in the extratropics due to their associated extreme winds.</p> </div><div> <p>Skillful predictions of MCAOs and extratropical winter storms on subseasonal timescales have been linked to the strength of the stratospheric polar vortex. Using ERA-Interim reanalysis (1979-2019) and ECMWF forecasts from the S2S Prediction Project database we investigate the stratospheric influence on surface extremes such as MCAOs and high-impact winter storms. Following weak stratospheric vortex extremes, anomalous circulation patterns accompanied by increased storminess over the eastern North Atlantic are found to be strong indicators for enhanced MCAOs in high- and mid-latitudes. Understanding the role of the stratosphere in subseasonal variability and predictability of cold air outbreaks and storm tracks during winter can provide a key for a reliable forecast of severe impacts.</p> </div>

scholarly journals Robust asymmetry of the future Arctic polar vortex is driven by tropical Pacific warming

2020 ◽  
Author(s):  
Shinji Matsumura ◽  
Koji Yamazaki ◽  
Takeshi Horinouchi
Keyword(s):  
North America ◽  
Climate Model ◽  
Polar Vortex ◽  
Tropical Pacific ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Stratospheric Polar Vortex ◽  
Model Simulations ◽  
The Future ◽  
Stratospheric Cooling

Abstract The wintertime Arctic stratospheric polar vortex is characterized by a circumpolar westerly jet, confining the coldest temperatures over the Arctic. The future stratosphere is globally dominated by a strong radiative cooling due to the increase in greenhouse gases, enhancing the Arctic cooling. However, we find that over North America, the Arctic stratospheric cooling is suppressed or rather warming occurs, whereas over Eurasia stratospheric cooling is most pronounced, leading to an asymmetric polar vortex, based on 21st century climate model simulations. There are many causes that drive polar vortex variability, such as Arctic sea ice loss, and midlatitude and tropical Pacific warming, which make future projections highly uncertain. Our model simulations demonstrate that tropical warming induces the asymmetric polar vortex. The eastern equatorial Pacific warming causes eastward-shifted teleconnection, which strengthens the polar vortex over Eurasia and weakens over North America by enhancing the vertical wave propagation into the stratosphere. The asymmetric polar vortex is projected to markedly develop in the 2030s, and so could also affect winter surface climate over mid- to high-latitudes of Eurasia in the near future.

scholarly journals Tropospheric forcing of the boreal polar vortex splitting in January 2003

2010 ◽  
Vol 28 (11) ◽  
pp. 2133-2148 ◽  
Author(s):  
D. H. W. Peters ◽  
P. Vargin ◽  
A. Gabriel ◽  
N. Tsvetkova ◽  
V. Yushkov
Keyword(s):  
Rossby Wave ◽  
Planetary Wave ◽  
Winter Season ◽  
Polar Vortex ◽  
Wave Activity ◽  
The Arctic ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Polar Vortex ◽  
Wave Trains

Abstract. The dynamical evolution of the relatively warm stratospheric winter season 2002–2003 in the Northern Hemisphere was studied and compared with the cold winter 2004–2005 based on NCEP-Reanalyses. Record low temperatures were observed in the lower and middle stratosphere over the Arctic region only at the beginning of the 2002–2003 winter. Six sudden stratospheric warming events, including the major warming event with a splitting of the polar vortex in mid-January 2003, have been identified. This led to a very high vacillation of the zonal mean circulation and a weakening of the stratospheric polar vortex over the whole winter season. An estimate of the mean chemical ozone destruction inside the polar vortex showed a total ozone loss of about 45 DU in winter 2002–2003; that is about 2.5 times smaller than in winter 2004–2005. Embedded in a winter with high wave activity, we found two subtropical Rossby wave trains in the troposphere before the major sudden stratospheric warming event in January 2003. These Rossby waves propagated north-eastwards and maintained two upper tropospheric anticyclones. At the same time, the amplification of an upward propagating planetary wave 2 in the upper troposphere and lower stratosphere was observed, which could be caused primarily by those two wave trains. Furthermore, two extratropical Rossby wave trains over the North Pacific Ocean and North America were identified a couple of days later, which contribute mainly to the vertical planetary wave activity flux just before and during the major warming event. It is shown that these different tropospheric forcing processes caused the major warming event and contributed to the splitting of the polar vortex.

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 On the Nonlinearity of Winter Northern Hemisphere Atmospheric Variability

2019 ◽  
Vol 76 (1) ◽  
pp. 333-356 ◽  
Author(s):  
A. Hannachi ◽  
W. Iqbal
Keyword(s):  
North Atlantic ◽  
Polar Vortex ◽  
Principal Component ◽  
Empirical Orthogonal Functions ◽  
The Arctic ◽  
Climate Change Signal ◽  
Two Dimensional ◽  
Orthogonal Functions ◽  
Local Flow ◽  
The North

Abstract Nonlinearity in the Northern Hemisphere’s wintertime atmospheric flow is investigated from both an intermediate-complexity model of the extratropics and reanalyses. A long simulation is obtained using a three-level quasigeostrophic model on the sphere. Kernel empirical orthogonal functions (EOFs), which help delineate complex structures, are used along with the local flow tendencies. Two fixed points are obtained, which are associated with strong bimodality in two-dimensional kernel principal component (PC) space, consistent with conceptual low-order dynamics. The regimes reflect zonal and blocked flows. The analysis is then extended to ERA-40 and JRA-55 using daily sea level pressure (SLP) and geopotential heights in the stratosphere (20 hPa) and troposphere (500 hPa). In the stratosphere, trimodality is obtained, representing disturbed, displaced, and undisturbed states of the winter polar vortex. In the troposphere, the probability density functions (PDFs), for both fields, within the two-dimensional (2D) kernel EOF space are strongly bimodal. The modes correspond broadly to opposite phases of the Arctic Oscillation with a signature of the negative North Atlantic Oscillation (NAO). Over the North Atlantic–European sector, a trimodal PDF is also obtained with two strong and one weak modes. The strong modes are associated, respectively, with the north (or +NAO) and south (or −NAO) positions of the eddy-driven jet stream. The third weak mode is interpreted as a transition path between the two positions. A climate change signal is also observed in the troposphere of the winter hemisphere, resulting in an increase (a decrease) in the frequency of the polar high (low), consistent with an increase of zonal flow frequency.

Impact of Arctic gateways closure on the Atlantic Meridional Overturning Circulation in the Pliocene

2021 ◽  
Author(s):  
Julia Weiffenbach ◽  
Michiel Baatsen ◽  
Anna von der Heydt
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
The Arctic ◽  
Bering Strait ◽  
Overturning Circulation ◽  
The North ◽  
Meridional Overturning

<p>The mid-Pliocene climate is the most recent geological period with a greenhouse gas concentration of approximately 400 ppmv, similar to the present day. Proxy reconstructions indicate enhanced warming in the high North Atlantic in the mid-Pliocene, which has been suggested to be a response to a stronger Atlantic Meridional Overturning Circulation (AMOC). PlioMIP2 ensemble results show a stronger AMOC and simulated North Atlantic sea surface temperatures (SSTs) match reconstructions better than PlioMIP1. A major difference between PlioMIP1 and PlioMIP2 is the closure of the Bering Strait and Canadian Archipelago in the Pliocene. Previous studies have shown that closure of these Arctic gateways leads to an enhanced AMOC due to altered freshwater fluxes in the Arctic.</p><p>Analysis of our Community Earth System Model (CESM1) simulations shows that the simulated increase in North Atlantic SSTs and strengthened AMOC in the Pliocene is a result of Pliocene boundary conditions rather than CO<sub>2</sub> concentration increase. Here we compare results from two runs with pre-industrial boundary conditions and 280 and 560 ppmv CO<sub>2</sub> concentrations and three runs with PlioMIP2 boundary conditions and 280, 400 and 560 ppmv CO<sub>2</sub> concentrations. Results show a 10-15% stronger AMOC in the Pliocene simulations as well as enhanced warming and saltening of the North Atlantic sea surface. While there is a stronger AMOC, the Atlantic northward ocean heat transport (OHT) in the Pliocene simulations only increases 0-3% with respect to the pre-industrial. Analysis indicates there is an altered relationship between the AMOC and OHT in the Pliocene, pointing to fundamentally different behavior of the AMOC in the Pliocene simulations. This is supported by a specific spatial pattern of deep water formation (DWF) areas in the Pliocene simulations that is significantly different from that of the pre-industrial. In the Pliocene simulations, DWF areas adjacent to south Greenland disappear and new DWF areas appear further southwards in the Labrador Sea off the coast of Newfounland. These results indicate that insight into the effect of the palaeogeographic boundary conditions is crucial to understanding the Pliocene climate and its potential as a geological equivalent to a future greenhouse climate.</p>

Lower Jurassic Amaltheidae (Ammonitina) in North America: paleobiogeography and tectonic implications

2001 ◽  
Vol 38 (10) ◽  
pp. 1439-1449 ◽  
Author(s):  
Paul L Smith ◽  
Howard W Tipper ◽  
David M Ham
Keyword(s):  
North America ◽  
North Atlantic ◽  
Lower Jurassic ◽  
The Arctic ◽  
Longitudinal Displacement ◽  
The North ◽  
East Pacific ◽  
Northwest Europe ◽  
Dispersal Route ◽  
North American Craton

The amaltheids are restricted temporally to the late Pliensbachian and geographically to the northern part of the northern hemisphere. Amaltheus stokesi is the only species that occurs in all areas of North America where amaltheids are found. The craton north of the Canada–U.S.A. border yields the most diverse amaltheid fauna, including six of the seven taxa known in North America. On Quesnellia and Stikinia, there are no endemic amaltheids, and diversity is low; A. stokesi increases in abundance northwards where, in Stikinia, A. margaritatus makes rare appearances. Wrangellia, with its rich Pliensbachian Tethyan and east Pacific faunas, is almost devoid of amaltheids, but its amaltheid fauna does include two specimens of A. viligaensis, an eastern Russian species that is unknown elsewhere in North America. Cratonal amaltheid faunas have more in common with those of northwest Europe than eastern Eurasia, suggesting that the Arctic and northern North Atlantic constituted the main dispersal route. Paleobiogeographic patterns on the major allochthonous terranes argue against terrane rotation and in support of post-Pliensbachian northward displacement relative to the North American craton. In addition, the presence of western Pacific faunal elements on Wrangellia suggests a more significant longitudinal displacement relative to the craton for this terrane compared to that for Quesnellia and Stikinia. The Chilliwack terrane of southwestern British Columbia is a Pliensbachian paleobiogeographic anomaly.

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