The mutual impact of weather regimes and the stratospheric circulation on European surface weather

2020 ◽  
Author(s):  
Christian M. Grams ◽  
Remo Beerli ◽  
Dominik Büeler ◽  
Daniela I. V. Domeisen ◽  
Lukas Papritz ◽  
...  
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Polar Vortex ◽  
Stratospheric Polar Vortex ◽  
Weather Regimes ◽  
The North ◽  
Weather Events ◽  
Surface Weather ◽  
The North Atlantic ◽  
Large Scale Flow

<p>Extreme states of the winter stratosphere, such as sudden stratospheric warmings (SSWs) or an extremely strong stratospheric polar vortex (SPV), can affect surface weather over the North-Atlantic European region on subseasonal time scales. Here we investigate the occurrence of Atlantic-European weather regimes during different stratospheric conditions in winter and their link to large-scale weather events in European sub-regions. We further elucidate if the large-scale flow regime in the North Atlantic at SSW onset determines the subsequent downward impact.</p><p>Anomalous stratospheric conditions modulate the occurrence of weather regimes which project strongly onto the NAO and the likelihood of their associated weather events. In contrast weather regimes which do not project strongly onto the NAO are not affected by anomalous stratospheric conditions. These regimes provide pathways to unexpected weather events in extreme stratospheric polar vortex states. For example, Greenland blocking (GL) and the Atlantic Trough (AT) regime are the most frequent large-scale flow patterns following SSWs. While in Central Europe GL provides a pathway to cold and calm weather, AT provides a pathway to warm and windy weather. The latter weather conditions are usually not expected after an SSW. Furthermore, we find that a blocking situation over western Europe and the North Sea (European Blocking) at the time of the SSW onset favours the GL response and associated cold conditions over Europe. In contrast, an AT response and mild conditions are more likely if GL occurs already at SSW onset. An assessment of forecast performance in ECMWF extended-range reforecasts suggests that the model tends to forecast too cold conditions following weak SPV states.</p><p>In summary, weather regimes and their response to anomalous SPV states importantly modulate the stratospheric impact on European surface weather. In particular the tropospheric impact of SSW events critically depends on the tropospheric state during the onset of the SSW. We conclude that a correct representation of weather regime life cycles in numerical models could provide crucial guidance for subseasonal prediction.</p><p> </p><p>References:</p><p>Beerli, R., and C. M. Grams, 2019: Stratospheric modulation of the large-scale circulation in the Atlantic–European region and its implications for surface weather events. Q.J.R. Meteorol. Soc., <strong>145</strong>, 3732–3750, doi:10.1002/qj.3653.</p><p>Domeisen, D. I. V., C. M. Grams, and L. Papritz, 2020: The role of North Atlantic-European weather regimes in the surface impact of sudden stratospheric warming events. Weather and Climate Dynamics Discussions, 1–24, doi:https://doi.org/10.5194/wcd-2019-16.</p>

scholarly journals Impact of Synoptic-Scale Wave Breaking on the NAO and Its Connection with the Stratosphere in ERA-40

2009 ◽  
Vol 22 (20) ◽  
pp. 5464-5480 ◽  
Author(s):  
Torben Kunz ◽  
Klaus Fraedrich ◽  
Frank Lunkeit
Keyword(s):  
North Atlantic ◽  
Wave Breaking ◽  
Large Scale ◽  
Polar Vortex ◽  
Synoptic Scale ◽  
Stratospheric Polar Vortex ◽  
Close Link ◽  
The North ◽  
The North Atlantic ◽  
The Impact

Abstract This observational study investigates the impact of North Atlantic synoptic-scale wave breaking on the North Atlantic Oscillation (NAO) and its connection with the stratosphere in winter, as derived from the 40-yr ECMWF Re-Analysis (ERA-40). Anticyclonic (AB) and cyclonic wave breaking (CB) composites are compiled of the temporal and spatial components of the large-scale circulation using a method for the detection of AB and CB events from daily maps of potential vorticity on an isentropic surface. From this analysis a close link between wave breaking, the NAO, and the stratosphere is found: 1) a positive feedback between the occurrence of AB (CB) events and the positive (negative) phase of the NAO is suggested, whereas wave breaking in general without any reference to AB- or CB-like behavior does not affect the NAO, though it preferably emerges from its positive phase. 2) AB strengthens the North Atlantic eddy-driven jet and acts to separate it from the subtropical jet, while CB weakens the eddy-driven jet and tends to merge both jets. 3) AB (CB) events are associated with a stronger (weaker) lower-stratospheric polar vortex, characterized by the 50-hPa northern annular mode. During persistent weak vortex episodes, significantly more frequent CB than AB events are observed concurrently with a significant negative NAO response up to 55 days after the onset of the stratospheric perturbation. Finally, tropospheric wave breaking is related to nonannular stratospheric variability, suggesting an additional sensitivity of wave breaking and, thus, the NAO to specific distortions of the stratospheric polar vortex, rather than solely its strength.

Importance of Stratospheric Polar Vortex Events for Seasonal Predictability of Sea Level Pressure over the North Atlantic and Europe

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

<p>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 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 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 sea level pressure (SLP), which is, over the Atlantic sector, strongly linked to the North Atlantic oscillation (NAO).<br>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 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 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 over the North Atlantic and Europe.</p>

scholarly journals Diversity of the Wintertime Arctic Oscillation Pattern among CMIP5 Models: Role of the Stratospheric Polar Vortex

2019 ◽  
Vol 32 (16) ◽  
pp. 5235-5250 ◽  
Author(s):  
Hainan Gong ◽  
Lin Wang ◽  
Wen Chen ◽  
Renguang Wu ◽  
Wen Zhou ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Arctic Oscillation ◽  
Climate Models ◽  
Polar Vortex ◽  
Cmip5 Models ◽  
Stratospheric Polar Vortex ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

AbstractThe wintertime Arctic Oscillation (AO) pattern in phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models displays notable differences from the reanalysis. The North Pacific center of the AO pattern is larger in the ensemble mean of 27 models than in the reanalysis, and the magnitude of the North Pacific center of the AO pattern varies largely among the models. This study investigates the plausible sources of the diversity of the AO pattern in the models. Analysis indicates that the amplitude of the North Pacific center is associated with the coupling between the North Pacific and North Atlantic, which in turn is primarily modulated by the strength of the stratospheric polar vortex. A comparative analysis is conducted for the strong polar vortex (SPV) and weak polar vortex (WPV) models. It reveals that a stronger stratospheric polar vortex induces more planetary waves to reflect from the North Pacific to the North Atlantic and more wave activity fluxes to propagate from the North Pacific to the North Atlantic in the SPV models than in the WPV models. Thus, the coupling of atmospheric circulation between the North Pacific and North Atlantic is stronger in the SPV models, which facilitates more North Pacific variability to be involved in the AO variability and induces a stronger North Pacific center in the AO pattern. The increase in vertical resolution may improve the simulation of the stratospheric polar vortex and thereby reduces the model biases in the North Pacific–North Atlantic coupling and thereby the amplitude of the North Pacific center of the AO pattern in models.

scholarly journals The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events

2020 ◽  
Vol 1 (2) ◽  
pp. 373-388 ◽  
Author(s):  
Daniela I. V. Domeisen ◽  
Christian M. Grams ◽  
Lukas Papritz
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Europe ◽  
Storm Track ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Weather Regimes ◽  
The North ◽  
Flow Evolution ◽  
The North Atlantic

Abstract. Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular in the North Atlantic–European (NAE) region. While the stratospheric forcing often projects onto the North Atlantic Oscillation (NAO), the tropospheric response to SSW events, if any, is highly variable, and what determines the existence, location, timing, and strength of the downward impact remains an open question. We here explore how the variable tropospheric response to SSW events in the NAE region can be characterized in terms of a refined set of seven weather regimes and if the tropospheric flow in the North Atlantic region around the onset of SSW events is an indicator of the subsequent downward impact. The weather regime analysis reveals the Greenland blocking (GL) and Atlantic trough (AT) regimes as the most frequent large-scale patterns in the weeks following an SSW. While the GL regime is dominated by high pressure over Greenland, AT is dominated by a southeastward-shifted storm track in the North Atlantic. The flow evolution associated with GL and the associated cold conditions over Europe in the weeks following an SSW occur most frequently if a blocking situation over western Europe and the North Sea (European blocking) prevailed around the SSW onset. In contrast, an AT regime associated with mild conditions over Europe is more likely following the SSW event if GL occurs already around SSW onset. For the remaining tropospheric flow regimes during SSW onset we cannot identify a dominant flow evolution. Although it remains unclear what causes these relationships, the results suggest that specific tropospheric states in the days around the onset of the SSW are an indicator of the subsequent tropospheric flow evolution in the aftermath of an SSW, which could provide crucial guidance for subseasonal prediction.

scholarly journals The role of North Atlantic-European weather regimes in the surface impact of sudden stratospheric warming events

2020 ◽  
Author(s):  
Daniela I. V. Domeisen ◽  
Christian M. Grams ◽  
Lukas Papritz
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Europe ◽  
Storm Track ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Weather Regimes ◽  
The North ◽  
The North Atlantic

Abstract. Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular over the North Atlantic and Europe. However, not all SSW events exhibit the same tropospheric response, if any, and it remains an open question what determines the existence, location, timing, and strength of the downward impact. We here explore the role of the state of the tropospheric flow in the North Atlantic region at the onset of SSW events for determining the subsequent surface impact. A refined definition of seven North Atlantic tropospheric weather regimes indicates the Greenland blocking (GL) and Atlantic Trough (AT) regimes as the most frequent large-scale patterns following the weeks after an SSW. While GL is dominated by high pressure over Greenland, AT is dominated by a southeastward shifted storm track in the North Atlantic. We find that a blocking situation over western Europe and the North Sea (European Blocking) at the time of the SSW onset favours the GL response and the associated cold conditions over Europe. In contrast, an AT response and mild conditions are more likely if GL occurs already at SSW onset. For the remaining tropospheric flow regimes during SSW onset, we find no clear response. The results indicate that the tropospheric impact of SSW events critically depends on the tropospheric state during the onset of the SSW, which could provide crucial guidance for subseasonal prediction.

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 Intensified Impact of Winter Arctic Oscillation on Simultaneous Precipitation Over the Mid–High Latitudes of Asia Since the Early 2000s

2021 ◽  
Vol 9 ◽  
Author(s):  
Haibo Zhou ◽  
Ke Fan
Keyword(s):  
North Atlantic ◽  
Rossby Waves ◽  
Polar Vortex ◽  
High Latitudes ◽  
Stratospheric Polar Vortex ◽  
Planetary Scale ◽  
The North ◽  
Subtropical Jet ◽  
The North Atlantic ◽  
Ao Mode

This study reveals an intensified impact of winter (November–February mean) Arctic Oscillation (AO) on simultaneous precipitation over the mid–high latitudes of Asia (MHA) since the early 2000s. The unstable relationship may be related to the changes in the tropospheric AO mode and the subtropical jet. Further analyses suggest that their changes may be attributable to the interdecadal changes in the stratospheric polar vortex. During 2002–2017, the anomalously weak stratospheric polar vortex is accompanied by intensified upward-propagating tropospheric planetary-scale waves anomalies. Subsequently, the stratospheric geopotential height anomalies over the North Atlantic high-latitudes propagate downward strongly, causing the changes in the tropospheric AO mode, that is, the positive height anomalies over the North Atlantic high-latitudes are stronger and extend southward, corresponding to the stronger and eastward extension of negative height anomalies over the North Atlantic mid-latitudes. Thus, the Rossby wave source anomalies over Baffin Bay and the Black Sea are strong, and correspondingly so too are their subsequently excited the Rossby waves anomalies. Meanwhile, the planetary-scale waves anomalies propagate weakly along the low-latitude waveguide, causing the intensified and southward shift of the subtropical jet. Therefore, the strong Rossby waves anomalies propagate eastward to the MHA. By contrast, during 1979–1999, the strong stratospheric polar vortex anomaly is accompanied by weak upward-propagating planetary-scale waves anomalies, resulting in weaker height anomalies over the North Atlantic mid–high latitudes. Consequently, the anomalous Rossby waves are weak. In addition, the subtropical jet weakens and shifts northward, which causes the Rossby waves anomalies to dominate over the North Atlantic, and thereby the impact of winter AO on simultaneous precipitation over the MHA is weak.

North Atlantic – European weather regimes in a changing climate: present and future

2020 ◽  
Author(s):  
Luise J. Fischer ◽  
Dominik Büeler ◽  
Christian M. Grams ◽  
Urs Beyerle ◽  
David N. Bresch ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
Future Climate ◽  
Climate Projections ◽  
Climate Conditions ◽  
Weather Regimes ◽  
The North ◽  
Surface Weather ◽  
The North Atlantic

<p>We present findings from an analysis of weather regimes over the North Atlantic and Europe in present and future climate conditions. Weather regimes strongly influence the statistical distribution of surface weather variables. We use a recently developed, all-season North Atlantic - European weather regime classification with seven regimes. These regimes were originally identified in ERA-Interim reanalyses and, in this study, we investigate how they are represented in climate simulations using the CESM1 large ensemble for present-day and future (RCP8.5) climate conditions. With these regimes, the classification of the flow conditions in the considered region goes beyond the classical categorization according to the North Atlantic oscillation index; the weather regimes explicitly capture different flavors of strong zonal flows and the occurrence of blocking over Greenland, Scandinavia, and Central Europe, respectively. In ERA-Interim they explain 70% of the variability in geopotential height at 500 hPa year-round. Our analysis quantifies how well CESM1 represents the statistics of the weather regimes in present-day climate and how strongly their frequencies change in the future climate scenario. In addition, we identify statistical relationships between weather regimes and their resulting impacts on spatial patterns of surface variables such as precipitation. We compare those patterns and characteristics of the weather regimes identified in ERA-Interim to their characteristics in simulations of present and future climate conditions.</p><p>This analysis leads to insight into the representation of and changes in atmospheric circulation in one particular climate model, and, at the same time, it quantifies how well the climate model captures the observed link between surface weather and weather regimes. This approach contributes to improving our understanding of atmospheric circulation changes and their impact on a regional scale, and it may benefit the interpretation and communication of climate projections.</p>

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.

Seasonal Predictability of Wintertime mid-latitude Cyclonic Activity over the North Atlantic and Europe

2021 ◽  
Author(s):  
Alvise Aranyossy ◽  
Sebastian Brune ◽  
Lara Hellmich ◽  
Johanna Baehr
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Jet Stream ◽  
Cyclonic Activity ◽  
Max Planck ◽  
Pressure System ◽  
Wind Speeds ◽  
Average Lifespan ◽  
The North ◽  
The North Atlantic

<p>We analyse the connections between the wintertime North Atlantic Oscillation (NAO), the eddy-driven jet stream with the mid-latitude cyclonic activity over the North Atlantic and Europe. We investigate, through the comparison against ECMWF ERA5 and hindcast simulations from the Max Planck Institute Earth System Model (MPI-ESM), the potential for enhancement of the seasonal prediction skill of the Eddy Kinetic Energy (EKE) by accounting for the connections between large-scale climate and the regional cyclonic activity. Our analysis focuses on the wintertime months (December-March) in the 1979-2019 period, with seasonal predictions initialized every November 1st. We calculate EKE from wind speeds at 250 hPa, which we use as a proxy for cyclonic activity. The zonal and meridional wind speeds are bandpass filtered with a cut-off at 3-10 days to fit with the average lifespan of mid-latitude cyclones. </p><p>Preliminary results suggest that in ERA5, major positive anomalies in EKE, both in quantity and duration, are correlated with a northern position of the jet stream and a positive phase of the NAO. Apparently, a deepened Icelandic low-pressure system offers favourable conditions for mid-latitude cyclones in terms of growth and average lifespan. In contrast, negative anomalies in EKE over the North Atlantic and Central Europe are associated with a more equatorward jet stream, these are also linked to a negative phase of the NAO.  Thus, in ERA5, the eddy-driven jet stream and the NAO play a significant role in the spatial and temporal distribution of wintertime mid-latitude cyclonic activity over the North Atlantic and Europe. We extend this connection to the MPI-ESM hindcast simulations and present an analysis of their predictive skill of EKE for wintertime months.</p>

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