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.

Improvement in Prediction of the Arctic Oscillation with a Realistic Ocean Initial Condition in a CGCM

2015 ◽  
Vol 28 (22) ◽  
pp. 8951-8967 ◽  
Author(s):  
Hae-Jeong Kim ◽  
Joong-Bae Ahn
Keyword(s):  
Arctic Oscillation ◽  
Polar Vortex ◽  
Polar Front ◽  
Forecast Skill ◽  
Sea Surface ◽  
The Arctic ◽  
Initial Condition ◽  
Stratospheric Polar Vortex ◽  
The Arctic Oscillation ◽  
Polar Front Jet

Abstract This study verifies the impact of improved ocean initial conditions on the Arctic Oscillation (AO) forecast skill by assessing the one-month lead predictability of boreal winter AO using the Pusan National University (PNU) coupled general circulation model (CGCM). Hindcast experiments were performed on two versions of the model, one does not use assimilated ocean initial data (V1.0) and one does (V1.1), and the results were comparatively analyzed. The forecast skill of V1.1 was superior to that of V1.0 in terms of the correlation coefficient between the predicted and observed AO indices. In the regression analysis, V1.1 showed more realistic spatial similarities than V1.0 did in predicted sea surface temperature and atmospheric circulation fields. The authors suggest the relative importance of the contribution of the ocean initial condition to the AO forecast skill was because the ocean data assimilation increased the predictability of the AO, to some extent, through the improved interaction between tropical forcing induced by realistic sea surface temperature (SST) and atmospheric circulation. In V1.1, as in the observation, the cold equatorial Pacific SST anomalies generated the weakened tropical convection and Hadley circulation over the Pacific, resulting in a decelerated subtropical jet and accelerated polar front jet in the extratropics. The intensified polar front jet implies a stronger stratospheric polar vortex relevant to the positive AO phase; hence, surface manifestations of the reflected positive AO phase were then induced through the downward propagation of the stratospheric polar vortex. The results suggest that properly assimilated initial ocean conditions might contribute to improve the predictability of global oscillations, such as the AO, through large-scale tropical ocean–atmosphere interaction.

scholarly journals Seasonal prediction of the boreal winter stratosphere

2021 ◽  
Author(s):  
Alice Portal ◽  
Paolo Ruggieri ◽  
Froila M. Palmeiro ◽  
Javier García-Serrano ◽  
Daniela I. V. Domeisen ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Polar Vortex ◽  
Seasonal Prediction ◽  
Wave Activity ◽  
Boreal Winter ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Eddy Heat Flux ◽  
Prediction Systems ◽  
Model Database

AbstractThe predictability of the Northern Hemisphere stratosphere and its underlying dynamics are investigated in five state-of-the-art seasonal prediction systems from the Copernicus Climate Change Service (C3S) multi-model database. Special attention is devoted to the connection between the stratospheric polar vortex (SPV) and lower-stratosphere wave activity (LSWA). We find that in winter (December to February) dynamical forecasts initialised on the first of November are considerably more skilful than empirical forecasts based on October anomalies. Moreover, the coupling of the SPV with mid-latitude LSWA (i.e., meridional eddy heat flux) is generally well reproduced by the forecast systems, allowing for the identification of a robust link between the predictability of wave activity above the tropopause and the SPV skill. Our results highlight the importance of November-to-February LSWA, in particular in the Eurasian sector, for forecasts of the winter stratosphere. Finally, the role of potential sources of seasonal stratospheric predictability is considered: we find that the C3S multi-model overestimates the stratospheric response to El Niño–Southern Oscillation (ENSO) and underestimates the influence of the Quasi–Biennial Oscillation (QBO).

scholarly journals Seasonal Prediction Skill of Northern Extratropical Surface Temperature Driven by the Stratosphere

2017 ◽  
Vol 30 (12) ◽  
pp. 4463-4475 ◽  
Author(s):  
Liwei Jia ◽  
Xiaosong Yang ◽  
Gabriel Vecchi ◽  
Richard Gudgel ◽  
Thomas Delworth ◽  
...  
Keyword(s):  
Climate Model ◽  
Lower Troposphere ◽  
Polar Vortex ◽  
Seasonal Prediction ◽  
The Arctic ◽  
Northern Eurasia ◽  
Stratospheric Polar Vortex ◽  
Near Surface ◽  
Predictive Skill

This study explores the role of the stratosphere as a source of seasonal predictability of surface climate over Northern Hemisphere extratropics both in the observations and climate model predictions. A suite of numerical experiments, including climate simulations and retrospective forecasts, are set up to isolate the role of the stratosphere in seasonal predictive skill of extratropical near-surface land temperature. It is shown that most of the lead-0-month spring predictive skill of land temperature over extratropics, particularly over northern Eurasia, stems from stratospheric initialization. It is further revealed that this predictive skill of extratropical land temperature arises from skillful prediction of the Arctic Oscillation (AO). The dynamical connection between the stratosphere and troposphere is also demonstrated by the significant correlation between the stratospheric polar vortex and sea level pressure anomalies, as well as the migration of the stratospheric zonal wind anomalies to the lower troposphere.

scholarly journals Seasonal prediction of boreal winter stratosphere

2020 ◽  
Author(s):  
Alice Portal ◽  
Paolo Ruggieri ◽  
Froila Palmeiro ◽  
Javier Garcìa-Serrano ◽  
Daniela Domeisen ◽  
...  
Keyword(s):  
Heat Flux ◽  
Empirical Relation ◽  
Polar Vortex ◽  
Seasonal Prediction ◽  
Arctic Sea Ice ◽  
Boreal Winter ◽  
Stratospheric Polar Vortex ◽  
Atmospheric Flow ◽  
Eddy Heat Flux ◽  
Using Data

<p>Advances in the development of seasonal forecast systems allow skillful predictions of the atmospheric flow in the extratropics. Recent studies have highlighted the importance of stratospheric processes in climate variability at seasonal time scales, while their representation and impact in seasonal prediction is yet to be understood. Here stratospheric variability and predictability in boreal winter are evaluated on the seasonal range, using multi-model retrospective forecasts initialised in November. A novel focus is adopted to assess troposphere-stratosphere coupling (i.e., the interaction between upper-tropospheric eddy heat flux and the stratospheric polar vortex) on the basis of the empirical relation derived by Hinssen and Ambaum (2010)<sup>[1]</sup>. Results indicate that dynamical predictions perform better than persistence forecasts and show significant skill up to lead season one (December to February). We find that seasonal anomalies of stratospheric zonal-mean zonal wind in the extratropics are mostly explained by anomalous tropospheric eddy heat flux; the response to tropospheric wave forcing is weaker in models than in reanalysis. Furthermore, we demonstrate that skillful seasonal stratospheric forecasts benefit from residual predictability of the heat flux over the Pacific sector, while further improvements are limited by current unpredictability of the Eurasian heat flux on the seasonal time scale. Sources of long-term predictability are examined and reveal a potential influence of the QBO, Arctic sea ice, Eurasian snow cover and ENSO. This work is realised using data from the seasonal Copernicus Climate Change Service multi-model (November initialisations from 1993 to 2016) and from ERA-Interim reanalysis.</p><p>[1] Hinssen,  Y. B. L. and Ambaum,  M. H. P.:  Relation between the 100-hPa heat flux and stratospheric potential vorticity, J. Atmos.Sci., 67, 4017–4027, 2010.</p>

scholarly journals Stratospheric Nudging And Predictable Surface Impacts (SNAPSI): A Protocol for Investigating the Role of the Stratospheric Polar Vortex in Subseasonal to Seasonal Forecasts

2022 ◽  
Author(s):  
Peter Hitchcock ◽  
Amy Butler ◽  
Andrew Charlton-Perez ◽  
Chaim Garfinkel ◽  
Tim Stockdale ◽  
...  
Keyword(s):  
Winter Season ◽  
Polar Vortex ◽  
Forecast Skill ◽  
The Arctic ◽  
Seasonal Forecasts ◽  
Stratospheric Polar Vortex ◽  
Near Surface ◽  
Forecast Models ◽  
The Impact

Abstract. Major disruptions of the winter season, high-latitude, stratospheric polar vortices can result in stratospheric anomalies that persist for months. These sudden stratospheric warming events are recognized as an important potential source of forecast skill for surface climate on subseasonal to seasonal timescales. Realizing this skill in operational subseasonal forecast models remains a challenge, as models must capture both the evolution of the stratospheric polar vortices in addition to their coupling to the troposphere. The processes involved in this coupling remain a topic of open research. We present here the Stratospheric Nudging And Predictable Surface Impacts (SNAPSI) project. SNAPSI is a new model intercomparison protocol designed to study the role of the Arctic and Antarctic stratospheric polar vortices in sub-seasonal to seasonal forecast models. Based on a set of controlled, subseasonal, ensemble forecasts of three recent events, the protocol aims to address four main scientific goals. First, to quantify the impact of improved stratospheric forecasts on near-surface forecast skill. Second, to attribute specific extreme events to stratospheric variability. Third, to assess the mechanisms by which the stratosphere influences the troposphere in the forecast models, and fourth, to investigate the wave processes that lead to the stratospheric anomalies themselves. Although not a primary focus, the experiments are furthermore expected to shed light on coupling between the tropical stratosphere and troposphere. The output requested will allow for a more detailed, process-based community analysis than has been possible with existing databases of subseasonal forecasts.

scholarly journals A strong phase reversal of the Arctic Oscillation in midwinter 2015/2016: Role of the stratospheric polar vortex and tropospheric blocking

2016 ◽  
Vol 121 (22) ◽  
pp. 13,443-13,457 ◽  
Author(s):  
Hoffman H. N. Cheung ◽  
Wen Zhou ◽  
Marco Y. T. Leung ◽  
C. M. Shun ◽  
S. M. Lee ◽  
...  
Keyword(s):  
Arctic Oscillation ◽  
Polar Vortex ◽  
The Arctic ◽  
Stratospheric Polar Vortex ◽  
Strong Phase ◽  
Phase Reversal ◽  
The Arctic Oscillation

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.

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.

scholarly journals Interannual Variability of the North American Cold Air Stream and Associated Synoptic Circulations

2017 ◽  
Vol 30 (23) ◽  
pp. 9575-9590 ◽  
Author(s):  
Yuki Kanno ◽  
John E. Walsh ◽  
Toshiki Iwasaki
Keyword(s):  
United States ◽  
Interannual Variability ◽  
Rocky Mountains ◽  
Arctic Oscillation ◽  
Potential Temperature ◽  
The Arctic ◽  
Boreal Winter ◽  
Stratospheric Polar Vortex ◽  
Cold Air ◽  
The Arctic Oscillation

In boreal winter, the cold air mass (CAM) flux of air with a potential temperature below 280 K forms climatological mean CAM streams in East Asia and North America (NA). This study diagnoses the interannual variability of the NA stream by an analysis of the CAM flux across 60°N between Greenland and the Rocky Mountains. The first empirical orthogonal function (EOF) represents the variations in intensity of the NA stream. When the first principal component (PC1) is highly positive, the central part of the NA stream is intensified, with cold anomalies east of the Rocky Mountains. At the same time, a stratospheric polar vortex tends to split or displace toward NA. PC1 is highly correlated with the tropical Northern Hemisphere pattern, implying that this pattern is associated with the intensity of the NA stream. The second EOF shows a longitudinal shift of the NA stream toward Greenland or the Rocky Mountains. A highly negative PC2 results in a cold anomaly from western Canada to the Midwestern United States and anomalous heavy snowfall in the northeastern United States. PC2 is positively correlated with the Arctic Oscillation, which suggests that the longitudinal position of the NA stream varies with the Arctic Oscillation. These results illustrate how the intensity and location of cold air outbreaks vary with large-scale modes of atmospheric variability, with corresponding implications for the predictability of winter severity in NA.

scholarly journals Volcanic activity sparks the Arctic Oscillation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Weizheng Qu ◽  
Fei Huang ◽  
Jinping Zhao ◽  
Ling Du ◽  
Yong Cao
Keyword(s):  
Volcanic Activity ◽  
Volcanic Eruption ◽  
Arctic Oscillation ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
The Arctic ◽  
Vortex System ◽  
Significant Fluctuation ◽  
The Arctic Oscillation

AbstractThe parasol effect of volcanic dust and aerosol caused by volcanic eruption results in the deepening and strengthening of the Arctic vortex system, thus stimulating or strengthening the Arctic Oscillation (AO). Three of the strongest AOs in more than a century have been linked to volcanic eruptions. Every significant fluctuation of the AO index (AOI = ΔH_middle latitudes − ΔH_Arctic) for many years has been associated with a volcanic eruption. Volcanic activity occurring at different locations in the Arctic vortex circulation will exert different effects on the polar vortex.

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