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

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.

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

Journal of Climate ◽

10.1175/jcli-d-20-0536.1 ◽

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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Volcanic activity sparks the Arctic Oscillation

Scientific Reports ◽

10.1038/s41598-021-94935-6 ◽

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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Internal variability of the Arctic Oscillation and its projections

10.5194/egusphere-egu2020-13027 ◽

2020 ◽

Author(s):

Annalisa Cherchi ◽

Paolo Oliveri ◽

Aarnout van Delden

Keyword(s):

Northern Hemisphere ◽

Arctic Oscillation ◽

Internal Variability ◽

The Arctic ◽

Positive Phase ◽

Cmip5 Models ◽

Modes Of Variability ◽

The Future ◽

The Arctic Oscillation

The Arctic Oscillation (AO) is one of the main modes of variability of the Northern Hemisphere winter, also referred as Northern Annular Mode (NAM). The positive phase of the AO is characterized by warming/cooling over Northern Eurasia and the United States and cooling over Canada, especially over eastern Canada. Its positive phase is also characterized by very dry conditions over the Mediterranean and wet conditions over Northern Europe. A positive trend of the AO is observed for the period 1951-2011 and it is captured in CMIP5 models only when GHG-only forcing are included. In CMIP5 models the change expected is mostly mitigated by the effects of the aerosols. When considering AR5 scenarios, the AO is projected to become more positive in the future, though with a large spread among the models.Overall the spread in the representation of the AO variability and trend is large also in experiments with present-day conditions, likely associated with the large internal variability. Unique tools to identify and measure the role of the internal variability in the model representation of the large-scale modes of variability are large ensembles where multiple members are built with different initial conditions.Here we use the NCAR Community Model Large Ensemble (CESM-LE) composing the historical period (1920-2005) to the future (2006-2100) in a RCP8.5 scenario to measure the role of the internal variability in shaping AO variability and changes. Potential predictability of the AO index is quantified in the historical and future periods, evidencing how the members spread remain large without specific trends in these characteristics. Preliminary results indicate that the internal variability has large influence on the AO changes and related implications for the Northern Hemisphere climate.

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Role of the Polar-night Jet Oscillation on the formation of the Arctic Oscillation in the Northern Hemisphere winter

Journal of Geophysical Research Atmospheres ◽

10.1029/2003jd004123 ◽

2004 ◽

Vol 109 (D11) ◽

Cited By ~ 49

Author(s):

Yuhji Kuroda

Keyword(s):

Northern Hemisphere ◽

Arctic Oscillation ◽

The Arctic ◽

Polar Night ◽

The Arctic Oscillation ◽

Hemisphere Winter ◽

Jet Oscillation ◽

Northern Hemisphere Winter

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

Journal of Climate ◽

10.1175/jcli-d-16-0475.1 ◽

2017 ◽

Vol 30 (12) ◽

pp. 4463-4475 ◽

Cited By ~ 26

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.

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The role of stratospheric resolution in simulating the Arctic Oscillation response to greenhouse gases

Geophysical Research Letters ◽

10.1029/2001gl014444 ◽

2002 ◽

Vol 29 (10) ◽

pp. 138-1-138-4 ◽

Cited By ~ 27

Author(s):

Nathan P. Gillett ◽

Myles R. Allen ◽

Keith D. Williams

Keyword(s):

Greenhouse Gases ◽

Arctic Oscillation ◽

The Arctic ◽

The Arctic Oscillation

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

10.5194/gmd-2021-394 ◽

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.

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High vs. low latitude influence on seasonal stratospheric pathways in the atmospheric model ICON

10.5194/egusphere-egu21-9573 ◽

2021 ◽

Author(s):

Raphael Köhler ◽

Dörthe Handorf ◽

Ralf Jaiser ◽

Klaus Dethloff

Keyword(s):

Large Scale ◽

Arctic Oscillation ◽

Southern Oscillation ◽

Polar Vortex ◽

Atmospheric Model ◽

The Arctic ◽

Late Winter ◽

Stratospheric Polar Vortex ◽

Enso Events ◽

Hemisphere Winter

Stratospheric pathways play an important role in connecting distant anomaly patterns to each other on seasonal timescales. As long-lived stratospheric extreme events can influence the large-scale tropospheric circulation on timescales of multiple weeks, stratospheric pathways have been identified as one of the main potential sources for subseasonal to seasonal predictability in mid-latitudes. These pathways have been shown to connect Arctic anomalies to lower latitudes and vice versa. However, there is an ongoing discussion on how strong these stratospheric pathways are and how they exactly work.&#160;In this context, we investigate two strongly discussed stratospheric pathways by analysing a suite of seasonal experiments with the atmospheric model ICON: On the one hand, the effect of El Ni&#241;o-Southern Oscillation (ENSO) on the stratospheric polar vortex, and thus the circulation in mid and high latitudes in winter. And on the other hand, the effect of a rapidly changing Arctic on lower latitudes via the stratosphere. The former effect is simulated realistically by ICON, and the results from the ensemble simulations suggest that ENSO has an effect on the large-scale Northern Hemisphere winter circulation. The ICON experiments and the reanalysis exhibit a weakened stratospheric vortex in warm ENSO years. Furthermore, in particular in winter, warm ENSO events favour the negative phase of the Arctic Oscillation, whereas cold events favour the positive phase. The ICON simulations also suggest a significant effect of ENSO on the Atlantic-European sector in late winter. Unlike the effect of ENSO, ICON simulations and the reanalysis do not agree on the stratospheric pathway for Arctic-midlatitude linkages. Whereas the reanalysis exhibits a weakening of the stratospheric vortex in midwinter and a connected tropospheric negative Arctic Oscillation circulation response to amplified Arctic warming, this is not the case in the ICON simulations. Implications and potential reasons for this discrepancy are further analysed and discussed in this work. &#160;

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