Winter Atmospheric Circulation Research Articles

Existence of typical winter atmospheric circulation patterns leading to high PM2.5 concentration days in East Asia

Understanding the atmospheric circulation patterns responsible for severe air pollution events in East Asia is important because East Asia is one of the most polluted regions in the world, particularly during the boreal winter (December-January-February). Here, by conducting GEOS-Chem simulation with fixed anthropogenic emission sources, we found that there exist three typical atmospheric circulation patterns conducive to leading to high concentrations of particulate matter with a diameter less than or equal to 2.5 μm (PM2.5) in East Asia. These atmospheric circulation patterns are characterized by weakened horizontal winds, which allows PM2.5 to accumulate, and by enhanced relative humidity, which can favor secondary formation of PM2.5. The occurrence of these atmospheric circulation patterns is associated with increased sea ice cover over the Barents Sea and heavy precipitation over the tropical western Indian Ocean. The existence of these atmospheric circulation patterns among typical atmospheric circulation patterns indicates high PM2.5 days in East Asia are unavoidable given current level of anthropogenic emissions in the region. This conclusion indicates that sustained efforts to reduce anthropogenic emission sources in East Asia should be warranted to avoid high PM2.5 days.

Skilful predictions of the Summer North Atlantic Oscillation

The Summer North Atlantic Oscillation is the primary mode of atmospheric variability in the North Atlantic region and has a significant influence on regional European, North American and Asian summer climate. However, current dynamical seasonal prediction systems show no significant Summer North Atlantic Oscillation prediction skill, leaving society ill-prepared for extreme summers. Here we show an unexpected role for the stratosphere in driving the Summer North Atlantic Oscillation in both observations and climate prediction systems. The anomalous strength of the lower stratosphere polar vortex in late spring is found to propagate downwards and influence the Summer North Atlantic Oscillation. Windows of opportunity are identified for useful levels of Summer North Atlantic Oscillation prediction skill, both in the 50% of years when the late spring polar vortex is anomalously strong/weak and possibly earlier if a sudden stratospheric warming event occurs in late winter. However, we show that model dynamical signals are spuriously weak, requiring large ensembles to obtain robust signals and we identify a summer ‘signal-to-noise paradox’ as found in winter atmospheric circulation Our results open possibilities for a range of new summer climate services, including for agriculture, water management and health sectors.

Diverse and high pollution of microplastics in seasonal snow across Northeastern China

Snow scavenging is recognized as one of the major sinks for atmospheric microplastics (MPs). However, little is known about the properties of MPs in large-scale surface snow. Using Nile Red staining and micro-Fourier transform infrared spectroscopy, we identified the shapes, sizes, and polymer components of MPs in seasonal snow across northeastern (NE) China, a major industrial area. The average concentration of MPs was (4.52 ± 3.05) × 104 MPs L−1, and the highest contamination (6.65 ± 3.89) × 104 MPs L−1 was observed in Changbai Mountains, which was the highest concentration observed in surface snow to the extent of literature. The majority of snow MPs were smaller than 50 μm and composed primarily of fragments. Ethylene vinyl acetate and polyethylene were the dominant contributors to their chemical components. Investigation with positive matrix factorization revealed that the MPs were primarily generated by debris from packaging materials, followed by industrial and construction activities. In addition, the winter atmospheric circulation over the northwestern Siberian and Mongolian plateaus likely dominated the wide-range dispersion and deposition of the MPs across NE China. These results provide a first comprehensive perspective of MPs from sources to removal associated with snow in a large geographic region.

Mid-Holocene pine forest expansion caused by the weakening of the East Asian winter monsoon and linked to climate change in the North Atlantic region

The East Asian winter monsoon (EAWM) system is one of the most active components of the global winter atmospheric circulation, and it has a major impact on the Eurasian climate in winter. However, relatively few proxy indicators are available to reconstruct the past evolution of the EAWM. Based on the physiology and modern distribution of the temperate forest and boreal forest in Northeast Asia, we found that the northern boundary of temperate pine forest is sensitive to winter temperature and thus it can be used as a proxy for EAWM intensity. A Holocene pollen record from Lake Woniupaozi in Northeast China shows that an expansion of temperate pine forest since ∼6.0 ka cal BP was linked to a weakening of the EAWM. This pattern is consistent with other paleoclimatic records from Northeast Asia and elsewhere, including the North Atlantic region, Middle East, Arabian Sea, and the Tibetan Plateau/Southwest China, which suggests a major climatic transition in the mid-Holocene. The mechanism responsible for this teleconnection may have been the continuous melting of the Laurentide ice which lowered the SST in the North Atlantic and maintained the North Atlantic Oscillation (NAO) in a positive winter phase. This influence was subsequently transmitted from the North Atlantic region to Eurasia via the winter southern Eurasian (SEA) teleconnection.

Occurrence of Winter Atmospheric Circulation Regimes in Euro-Atlantic Region and Associated Extreme Weather Anomalies in the Northern Hemisphere

Occurrence of Winter Atmospheric Circulation Regimes in Euro-Atlantic Region and Associated Extreme Weather Anomalies in the Northern Hemisphere

Nonlinear Effects of the Stratospheric Quasi‐Biennial Oscillation and ENSO on the North Atlantic Winter Atmospheric Circulation

AbstractPrevious studies have shown that both the stratospheric Quasi‐Biennial Oscillation (QBO) and the El Niño‐South Oscillation (ENSO) can influence the North Atlantic winter circulation. Here we use reanalysis and model output data to show that the QBO and ENSO interact to produce a nonlinear effect on the North Atlantic winter circulation. Specifically, during El Niño winters, the QBO teleconnection mainly takes a subtropical pathway with changes in the North Pacific–Atlantic subtropical jet (STJ); during La Niña winters, the QBO connects with the troposphere predominantly through a polar pathway, that is, stratospheric polar vortex (SPV) changes. Further, the QBO‐induced STJ changes in El Niño lead to anomalous Rossby wave propagation toward the North Atlantic, and the QBO‐induced SPV during La Niña anomaly exerts a downward effect on the North Atlantic. Hence, the various interactions between ENSO and QBO teleconnections result in nonlinear, and even synergistic, impacts on the North Atlantic circulation.

Synergistic Effects of Upstream Disturbances and Oceanic Fronts on the Subseasonal Evolution of Western Pacific Jet Stream in Winter

AbstractThe Western Pacific jet stream (WPJS) is an essential part of atmospheric circulation in winter, which significantly influences the weather and climate of the North Pacific and North America. In this paper, the characteristics and mechanism of WPJS subseasonal variation in winter are investigated. The upstream atmospheric disturbances in the East Asian polar‐front jet and subtropical jet merge over the Northwestern Pacific to form the subseasonal variability in WPJS, which has a significant period of 40–60 days. During the positive phase events of subseasonal WPJS, the convergence position of the upstream atmospheric disturbances shifts southwardly accompanied with the local enhancement and eastward extension of subseasonal WPJS. On the other hand, the subseasonal WPJS divides into the southern and northern westerly branches during the negative phase events. By the horizontal propagation of local Eliassen‐Palm fluxes in the upper atmosphere, the northward drift of the upstream atmospheric disturbances convergence dominates the delayed acceleration of the northern upper westerly branch. However, the intensification of atmospheric baroclinicity and upward baroclinic energy caused by the leading strong subtropical frontal zone determine the acceleration of the southern upper westerly branch.

The Influences of the Multi‐Scale Sea Surface Temperature Anomalies in the North Pacific on the Jet Stream in Winter

AbstractUsing Climate Forecast System Reanalysis (CFSR) data and numerical simulations, the impacts of the multi‐scale sea surface temperature (SST) anomalies in the North Pacific on the boreal winter atmospheric circulations are investigated. The basin‐scale SST anomaly as the Pacific Decadal Oscillation (PDO) pattern, a narrow meridional band of frontal‐scale smoothed SST anomaly in the subtropical front zone (STFZ) and the spatial dispersed eddy‐scale SST anomalies within the STFZ are the three types of forcings. The results of statistical methods find that all three oceanic forcings may correspond to the winter North Pacific jet changing with the similar pattern. Furthermore, several atmospheric general circulation model simulations are used to reveal the differences and detail processes of the three forcings. The basin‐scale cold PDO‐pattern SST anomaly first causes negative turbulent heat flux anomalies, atmospheric cooling, and wind deceleration in the lower atmosphere. Subsequently, the cooling temperature with an amplified southern lower temperature gradient and baroclinity brings a lagging middle warming because of the enhanced atmospheric eddy heat transport. The poleward and upward development of baroclinic fluctuations eventually causes the acceleration of the upper jet. The smoothed frontal‐ and eddy‐scales SST anomalies in the STFZ cause comparable anomalous jet as the basin‐scale by changing the upward baroclinic energy and Eliassen‐Palm fluxes. The forcing effects of multi‐scales SST anomalies coexist simultaneously in the mid‐latitude North Pacific, which can cause similar anomalous upper atmospheric circulations. This is probably why it is tricky to define the certain oceanic forcing to the specific observed atmospheric circulation variation.

On the Influence of ENSO on Sudden Stratospheric Warmings

AbstractUsing the extended ERA5 reanalysis and three state‐of‐the‐art models, this study explores how El Niño‐Southern Oscillation (ENSO) can influence the total frequency, seasonal cycle and preconditioning of sudden stratospheric warmings (SSWs). Reanalysis data shows that in the last seven decades, winters with SSWs were more common than winters without, regardless El Niño (EN) or La Niña (LN) occurrence or the ENSO/SSW definitions. In agreement with previous studies, our models tend to simulate a linear ENSO‐SSW relationship, with more SSWs for EN, around mid‐winter (January–February) as in reanalysis, and less for LN when compared to neutral conditions. Independently of ENSO, the main tropospheric precursor of SSWs appears to be an anomalous wave‐like pattern over Eurasia, but it is dominated by wavenumber 1 (WN1) for EN and shows an enhanced wavenumber 2 (WN2) for LN. The differences in this Eurasian wave pattern, which is largely internally generated, emerge from the distinct configuration of the background, stationary wave pattern induced by ENSO in the North Pacific, favoring a stronger WN1 (WN2) component during EN (LN). Our results suggest that the ENSO‐forced signal relies on modulating the seasonal‐mean polar vortex strength, becoming weaker and more displaced (stronger and more stable) for EN (LN), while ENSO‐unforced wave activity represents the ultimate trigger of SSWs. This supports the view that ENSO and SSWs are distinct sources of variability of the winter atmospheric circulation operating at different time‐scales and may reconcile previous findings in this context.

Impact of Ural Blocking on Early Winter Climate Variability Under Different Barents‐Kara Sea Ice Conditions

AbstractUral blocking (UB) is a prominent mode of variability of the Northern Hemisphere atmospheric circulation, particularly in fall. It can persist for several days and exert a lagged influence on the wintertime NH circulation, providing predictability at the subseasonal time scale. Using two atmospheric models, we explore how the early winter atmospheric circulation responds to a 2‐week persistent UB anomaly imposed in early November. Experiments are carried out with two different configurations of Barents‐Kara (BK) sea‐ice concentration to examine whether it plays a role in how UB impacts atmospheric variability. In both models, the UB anomaly is followed by a weakening of the stratospheric polar vortex and a negative phase of the North Atlantic Oscillation (NAO), which lasts up to 2 months after the forcing is released. Interestingly, the response is more persistent under low BK sea‐ice conditions, that is, BK sea ice modulates the atmospheric response to UB. Additional experiments with prescribed sea ice concentration anomalies alone suggest that BK sea ice exerts a limited influence on early winter NH atmospheric variability. The response to UB involves a weakening of the polar vortex that persists longer under low BK sea ice, which explains the more persistent response in that configuration. Our study highlights that UB variability in November is a robust precursor for early winter NAO/polar stratosphere anomalies, and this may be more relevant in the context of declining Arctic sea‐ice extent. Provided that climate models accurately capture this teleconnection, it has the potential to improve subseasonal predictions of the NH wintertime climate.

The Role of Coupled North Pacific Atmosphere–Ocean Interactions in Impacts of Tibetan Plateau Snow Anomalies on the Northern Hemisphere Winter Atmospheric Circulation

Abstract Previous studies indicate observed influences of autumn and winter Tibetan Plateau (TP) snow-cover anomalies on the winter Pacific–North American (PNA) teleconnection. This study simulates atmospheric and oceanic responses to persistent autumn–winter TP snow forcing using an atmospheric general circulation model (AGCM) and a coupled atmospheric-oceanic general circulation model (AOGCM), and quantifies the role of atmosphere–ocean interactions over North Pacific in TP snow effects. The AOGCM experiment induces a stronger and more realistic remote PNA response to heavy TP snow anomalies, and also a significant winter horseshoe-like North Pacific sea surface temperature (SST) pattern resulting from an anomalous equivalent barotropic cyclone, or a strengthened Aleutian low, with associated cyclonic wind stress anomalies. The horseshoe-like SST anomaly pattern is used as boundary forcing (without prescribed heavy TP snow) in another AOGCM experiment, which simulates an enhanced winter Aleutian low and a PNA-like response similar to the original AOGCM responses, indicating that that the direct Pacific–North American atmospheric response to persistent TP snow forcing in the AGCM is amplified in the AOGCM by the North Pacific midlatitude atmosphere–ocean interactions. This suggests that the mechanisms of the winter PNA responses to TP snow forcing involve dynamical atmospheric processes such as horizontal propagation of Rossby wave energy and transient eddy feedbacks, and also North Pacific atmosphere–ocean interactions, which provide a positive feedback on the development of the remote PNA teleconnection. Significance Statement The Tibetan Plateau has a 2.5 million km2 area and a 4000 m average elevation, and is often called “the third pole” because of its polar-like climate in midlatitude Eurasia. A heavy Tibetan Plateau snow cover increases the albedo effect and causes tropospheric cold temperature and low height changes that can be carried or advected to the North Pacific by the prevailing westerlies. The purpose of this study is to better understand how Tibetan Plateau snow anomalies influence the North Pacific and the remote atmospheric circulation through numerical simulations. Our results find that those North Pacific responses amply the direct atmospheric response to Tibetan Plateau snow-cover anomalies. This greatly improves our understanding of physical mechanisms of Tibetan Plateau snow impacts.

Summer Arctic Atmospheric Circulation and Its Association With the Ensuing East Asian Winter Monsoon Variability

AbstractThe impact of autumn Arctic sea ice reduction on the winter climate in Eurasia has been widely studied, but the role of the atmospheric circulation of the preceding summer has been mostly neglected. This study investigates a linkage between the summer Arctic circulation anomaly and the ensuing East Asian Winter Monsoon (EAWM) variability. The Arctic circulation anomaly, characterized by an anomalous anti‐cyclone occupying the Arctic Ocean and its marginal seas, can strongly melt Arctic sea ice in the Kara Sea‐Laptev Sea‐East Siberian Sea‐Chukchi Sea‐Beaufort Sea through dynamic and thermodynamic processes. The combination of the summer anti‐cyclone (cyclone) anomaly and light (heavy) autumn sea ice leads to an enhanced (weakened) EAWM. By introducing the coupling relationship between summer circulation and autumn sea ice into numerical experiments, the Community Atmospheric Model version 4 model has a good capability for capturing EAWM variability. Nevertheless, the dominant features of EAWM variability cannot be reproduced when the autumn sea ice mismatches the preceding summer circulation in the model. Therefore, the preceding summer circulation may modulate the impact of sea ice on Eurasia to some extent, which may increase uncertainties in the impact of Arctic sea ice loss on winter atmospheric circulation variability.

Enhanced Impact of Autumn North Tropical Atlantic Sea Surface Temperature Anomalies on Subsequent Winter Snowfall in Northeast China after 2001

Abstract This study reveals that the relationship between autumn north tropical Atlantic (NTA) sea surface temperature (SST) anomalies and Northeast China’s winter snowfall (NECWS) undergoes a remarkable interdecadal enhancement after 2001. Previous research confirmed that the relationship between the NTA SST anomaly and atmospheric circulation experienced interdecadal changes after the 2000s and suggested various reasons for this phenomenon. During 1961–2000, the NTA SST anomaly has a significantly positive correlation with other oceans, especially the tropical Indian Ocean (TIO), and the latter modulates the former’s impact on atmospheric circulations over the Eurasian continent with a cancelling effect, which results in a weaker relationship of the NTA SST anomaly and NECWS. In contrast, the warm NTA SST anomaly is relatively independent from other oceans during 2001–20, and it proves to be the forcing factor for NECWS since its solo influence on the winter atmospheric circulations initiated from the North Atlantic to East Asia is more robust, featuring the negative phase of the North Atlantic Oscillation and a downstream quasi-barotropic Rossby wave train over the mid- to high latitudes of Eurasian continent. Accordingly, together with the deepened East Asian trough and the strongly northward transported humid and warm air from the western Pacific, the local significantly enhanced ascending motions with cooling temperature favor much more NECWS. The linear baroclinic model simulates the effects of NTA and TIO SST anomalies on winter atmospheric circulations, corroborating the aforementioned results. Such results can be used for the prediction of NECWS with respect to the precursor of the autumn NTA SST anomaly.

Occurrence of winter atmospheric circulation regimes in Euro-Atlantic region and associated extreme weather anomalies in the Northern Hemisphere

Occurrence of winter atmospheric circulation regimes in Euro-Atlantic region and associated extreme weather anomalies in the Northern Hemisphere

Impacts of Observed Extreme Antarctic Sea Ice Conditions on the Southern Hemisphere Atmosphere

The Antarctic sea ice has undergone dramatic changes in recent years, with the highest recorded sea ice extent in 2014 and the lowest in 2017. We investigated the impacts of the observed changes in these two extremes of Antarctic sea ice conditions on the atmospheric circulation in the Southern Hemisphere. We conducted three numerical simulations with different seasonal cycles of Antarctic sea ice forcings using the Community Atmosphere Model Version 5: the maximum sea ice extent in 2014 (ICE_14), the minimum sea ice extent in 2017 (ICE_17), and the average sea ice extent between 1981 and 2010 (ICE_clm, reference simulation). Our results suggest that the atmospheric response in the Southern Hemisphere showed strong seasonal variations and the atmospheric circulation in winter was more sensitive to the decreased Antarctic sea ice in 2017 than the increased sea ice in 2014. In ICE_14, the westerlies over the polar region were enhanced in summer, but there was no significant change in the zonal-averaged wind in winter. In contrast, in ICE_17, there was a clear equatorward shift in the subtropical jet in winter, but no significant change in summer. The temperature responses were limited to the Antarctic coast, where there were changes in the sea ice in ICE_14 and ICE_17. The warming on the coast of the Amundsen Sea in summer led to a slight increase in precipitation in both simulations.

Climate models fail to capture strengthening wintertime North Atlantic jet and impacts on Europe.

Projections of wintertime surface climate over Europe depend on reliable simulations of the North Atlantic atmospheric circulation from climate models. However, it is unclear whether these models capture the long-term observed trends in the North Atlantic circulation. Here, we show that over the period from 1951 to 2020, the wintertime North Atlantic jet has strengthened, while model trends are, on average, only very weakly positive. The observed strengthening is greater than in any one of the 303 simulations from 44 climate models considered in our study. This divergence between models and observations is now much more apparent because of a very strong jet observed over the past decade. The models similarly have difficulty capturing the observed precipitation trends over Europe. Our results suggest that projections of winter atmospheric circulation and associated precipitation over Europe may be unreliable because they fail to capture the response to human emissions or underestimate the magnitude of multidecadal-to-centennial time scale internal variability.

Pacific Decadal Oscillation modulates the Arctic sea-ice loss influence on the midlatitude atmospheric circulation in winter

Abstract. The modulation of the winter impacts of Arctic sea-ice loss by the Pacific Decadal Oscillation (PDO) is investigated in the IPSL-CM6A-LR ocean–atmosphere general circulation model. Ensembles of simulations are performed with constrained sea-ice concentration following the Polar Amplification Model Intercomparison Project (PAMIP) and initial conditions sampling warm and cold phases of the PDO. Using a general linear model, we estimate the simulated winter impact of sea-ice loss, PDO and their combined effects. On the one hand, a negative North Atlantic Oscillation (NAO)-like pattern appears in response to sea-ice loss together with a modest deepening of the Aleutian Low. On the other hand, a warm PDO phase induces a large positive Pacific–North America pattern, as well as a small negative Arctic Oscillation pattern. Both sea-ice loss and warm PDO responses are associated with a weakening of the poleward flank of the eddy-driven jet, an intensification of the subtropical jet and a weakening of the stratospheric polar vortex. These effects are partly additive; the warm PDO phase therefore enhances the response to sea-ice loss, while the cold PDO phase reduces it. However, the effects of PDO and sea-ice loss are also partly non-additive, with the interaction between both signals being slightly destructive. This results in small damping of the PDO teleconnections under sea-ice loss conditions, especially in the stratosphere. The sea-ice loss responses are compared to those obtained with the same model in atmosphere-only simulations, where sea-ice loss does not significantly alter the stratospheric polar vortex.

Early‐to‐Late Winter 20th Century North Atlantic Multidecadal Atmospheric Variability in Observations, CMIP5 and CMIP6

AbstractThe strong multidecadal variability in North Atlantic (NA) winter atmospheric circulation is poorly understood and appears too weak in climate models. Recent research has shown peak atmospheric multidecadal variability over the NA in late winter, particularly March, linked to Atlantic multidecadal variability (AMV) of the ocean. Here a range of NA atmospheric circulation indices are assessed to provide a comprehensive picture of early‐to‐late winter low‐frequency variability and its representation in the latest generation of climate models (Coupled Model Intercomparison Project Phase 6 [CMIP6]). As found for CMIP5, CMIP6 models exhibit too‐weak multidecadal NA atmospheric variability compared to reanalysis data over the period 1862–2005. Consistent with previous research, the eastern part of the NA westerly jet (U700NA) exhibits peak low‐frequency variability in March. However, for NA‐wide jet speed and the NAO, low‐frequency variability and model‐reanalysis discrepancies are strongest in January and February, associated with too‐weak NA ocean‐atmosphere linkages.

Response of Eurasian Temperature to Barents–Kara Sea Ice: Evaluation by Multi‐Model Seasonal Predictions

AbstractBarents–Kara (BK) sea ice conditions are considered a potential source of seasonal predictability in the midlatitudes, but confirmation or refutation of this possibility remains elusive. We focused on the Warm Arctic–Cold Eurasia (WACE) pattern and evaluated whether BK sea ice is related to winter conditions over Eurasia in multi‐model seasonal predictions. In the models analyzed, the WACE index is strongly depended on the BK temperature and did not rigorously reflect a sea ice–Eurasia causal link. The autumn BK sea ice anomaly was not a precursor of winter atmospheric conditions over Eurasia. Rather, the winter atmospheric circulation likely drives both winter BK sea ice and Eurasian temperature. However, the predicted winter sea ice–Eurasia links are likely weaker than the observed. This contrast is speciously related to the modest sea ice variance, but the actual influence of BK sea ice variation on Eurasian temperature anomalies is still questionable.

Robust but weak winter atmospheric circulation response to future Arctic sea ice loss

The possibility that Arctic sea ice loss weakens mid-latitude westerlies, promoting more severe cold winters, has sparked more than a decade of scientific debate, with apparent support from observations but inconclusive modelling evidence. Here we show that sixteen models contributing to the Polar Amplification Model Intercomparison Project simulate a weakening of mid-latitude westerlies in response to projected Arctic sea ice loss. We develop an emergent constraint based on eddy feedback, which is 1.2 to 3 times too weak in the models, suggesting that the real-world weakening lies towards the higher end of the model simulations. Still, the modelled response to Arctic sea ice loss is weak: the North Atlantic Oscillation response is similar in magnitude and offsets the projected response to increased greenhouse gases, but would only account for around 10% of variations in individual years. We further find that relationships between Arctic sea ice and atmospheric circulation have weakened recently in observations and are no longer inconsistent with those in models.