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Composite anomalies of (a)-(c) geopotential height at 300 hPa (contours; in intervals of 20 m, significant values at the 95% confidence level are represented by thick lines) and 850 hPa (shadings; significant values at the 95% confidence level are represented by gray dots), (d)-(f) vertical cross sections of geopotential height (contours; in intervals of 20 m) and potential temperature (shadings) along thick red lines in (a)-(c), and (g)-(i) temperature (shadings; significant values at the 95% confidence level are represented by gray dots) and winds (vectors) at 850 hPa during day 22 to day 12 relative to all cold surge occurrences for the entire analysis period.
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The present study reveals the changes in the characteristics of cold surges over East Asia associated with the Arctic Oscillation (AO). Based on circulation features, cold surges are grouped into two general types: wave train and blocking types. The blocking type of cold surge tends to occur during negative AO periods, that is, the AO-related polar...
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... further manifest the mechanism of the cold surges initiated and developed by the upper-level wave train, Fig. 3 shows composite anomalies to depict the time evolutions of Z at 300 hPa and 850 hPa, vertical cross sections of Z and potential temperature, and tempera- ture and horizontal wind at 850 hPa averaged for the 332 cold surges. Significant fluctuations of ridge, trough, and ridge are alternately situated around the Ural Moun- tains ...
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... and tempera- ture and horizontal wind at 850 hPa averaged for the 332 cold surges. Significant fluctuations of ridge, trough, and ridge are alternately situated around the Ural Moun- tains (508-758N, 508-908E), Lake Baikal (458-658N, 908- 1208E), and Korea-Japan (308-458N, 1208-1408E) on day 22 relative to the occurrence date of cold surges (Fig. 3a). The ridge-trough-ridge pattern, implying a wave train across the Eurasian continent, aligns in a northwest-southeast direction across East Asia. The upper-tropospheric wave train appears to propagate southeastward (Figs. 3a-c). The anticyclone-cyclone couplet over Siberia and East Asia is also found at the lower troposphere on day 0, ...
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... (458-658N, 908- 1208E), and Korea-Japan (308-458N, 1208-1408E) on day 22 relative to the occurrence date of cold surges (Fig. 3a). The ridge-trough-ridge pattern, implying a wave train across the Eurasian continent, aligns in a northwest-southeast direction across East Asia. The upper-tropospheric wave train appears to propagate southeastward (Figs. 3a-c). The anticyclone-cyclone couplet over Siberia and East Asia is also found at the lower troposphere on day 0, which also exhibits a south- eastward propagation. At the lower troposphere, the anticyclone progresses from Siberia to southern China along the propagation of the wave train, linked to an expansion of the Siberian high toward ...
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... to southern China along the propagation of the wave train, linked to an expansion of the Siberian high toward East Asia. The Z feature at the upper troposphere shifts slightly west- ward compared to that at the lower troposphere. West- ward tilting with height is the obvious structure in the vertical cross section of Z along the waveguided line (Figs. 3d-f). Throughout the troposphere (i.e., below 300 hPa), troughs and ridges tilt westward with height, and warm and cold cores have opposite tilts. The Z and potential temperature patterns show a phase difference. Overall, the tilted warming-ridge and cooling-trough structure characterizes the baroclinic growth system of extratropical ...
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... growth system of extratropical cyclones, which intensify upper-level troughs and ridges (Holton 2004, 146-147). On day 12, the baroclinicity of the wave train weakens slightly. The Z patterns of both upper and lower troposphere over Lake Baikal show a nearly in-phase feature and the vertical cross section exhibits equivalent barotropic structure (Figs. ...
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... 3g-i depict the flows induced by lower- tropospheric Z patterns and the related temperature anomalies at 850 hPa. A strong northerly flow is formed by the anticyclone-cyclone couplet noted in Fig. 3b and is closely linked to the occurrence of cold surges (Fig. 3h). Interestingly, the temperature pattern matches well with the 300-hPa Z pattern shown in Figs. 3a-c. In the de- veloping baroclinic wave systems, upper-tropospheric troughs are located over the west of the lower-level low pressures because of the westward tilting of Z. ...
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... 3g-i depict the flows induced by lower- tropospheric Z patterns and the related temperature anomalies at 850 hPa. A strong northerly flow is formed by the anticyclone-cyclone couplet noted in Fig. 3b and is closely linked to the occurrence of cold surges (Fig. 3h). Interestingly, the temperature pattern matches well with the 300-hPa Z pattern shown in Figs. 3a-c. In the de- veloping baroclinic wave systems, upper-tropospheric troughs are located over the west of the lower-level low pressures because of the westward tilting of Z. Thus, cold advection also lies to the west of low pressures at the ...
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... with the result of Jeong and Ho (2005). Figure 4 shows the composite patterns of anomalies of Z at 300 and 850 hPa, vertical cross sections of Z and potential temperature, and 850-hPa temperature and horizontal wind for the 31 cold surges during positive AO. The general features relevant to wave train bear a resemblance to those shown in Fig. 3 in spite of several disparities. The upper-tropospheric ridge-trough-ridge pattern in a northwest-southeast direction from central Russia to Japan is found with a westward tilt relative to the pattern at the lower troposphere. It moves south- eastward toward East Asia with an expansion of the Siberian high (Figs. 4a-c). The vertical ...
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... weakens the Siberian high and the Aleutian low ( Thompson and Wallace 1998), which is linked to a weakening of the anticyclone-cyclone couplet with a high near the Siberian high and a low near the southwestern edge of the Aleutian low (Figs. 4a-c). In particular, the negative Z anomalies at 850 hPa over Japan in Fig. 4b are weaker than those in Fig. 3b. By these circulation patterns, the amplitude of the cold anomaly over East Asia is smaller than that shown in Figs. 3g-i and the cold advection is associated with anomalous north- westerly flow (Figs. 4g-i), instead of anomalous northerly flow. Because the anomalous cyclone over Japan is par- ticularly weak, this northwesterly flow ...
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Citations
... Previous studies have indicated the close relationship between the EAWM anomaly and the cold wave outbreaks (Lau and Chang 1987;Wang et al. 2006). In addition, extensive studies have shown that the occurrence and development of cold waves are closely related to the Arctic Oscillation (AO), the Siberian High, the Northern Hemisphere polar vortex, and mid-to-high latitude blocking highs (Zhang and Wang 1997;Jeong and Ho 2005;Park et al. 2011). In particular, the Siberian High, located in the lower troposphere, is the source of cold air that intrudes China. ...
... For most types of the cold waves, the SLP and Z500 anomalies in the polar region are predominantly positive, corresponding to a negative AO phase. This aligns with previous studies regarding the more occurrence of cold waves in the negative AO phase (Park et al. 2011). In contrast, in the NW-type of cold waves, the negative Z500 and SLP anomalies are mainly exhibited in the polar region, featuring a positive AO phase. ...
Cold waves are the most frequent winter disaster in China. Using Rotated Empirical Orthogonal Function (REOF) analysis, we categorize winter cold waves in China during 1983–2022 into four types based on their occurrence areas: East China (EC), Northwest China (NW), North China (NC), and Northeast China (NE). Each type exhibits distinct spatial–temporal characteristics and atmospheric circulation patterns. Prior to each cold wave outbreak, a baroclinic structure forms in the middle and lower troposphere, with low-pressure systems in central regions. As the cold wave develops, an anomalous high-pressure system moves from the northwest, replacing the low-pressure system but with varying intensity among the four regions. Notably, NW-type cold waves display negative sea level pressure anomalies over the polar region, linked to a weak positive Arctic Oscillation (AO) phase. Whereas, the EC, NC, and NE types of cold waves generally occur during a negative AO phase. The size and intensity of the Siberian High and Aleutian Low also vary among them, with the EC-type cold waves having the strongest values. Subseasonal prediction skills for these types of cold waves are assessed using the hindcasts of NUIST CFS1.1 model, which shows good prediction skill one pentad in advance but struggles beyond two pentads. At 2-pentad lead, the model starts to underestimate atmospheric circulation anomalies—particularly the Siberian High and northerly winds—resulting in insufficient cold air from north and weaker cold advection, leading to underestimated cold waves.
... Accordingly, predictions and interest in temperature fluctuations are increasing. In particular, increases in the unexpected variability of winter temperatures in East Asia significantly impact social, economic, and human activities [3][4][5]. Therefore, understanding East Asian temperature variability drives the need for more research. ...
The complex interaction between the Pacific decadal oscillation (PDO) and East Asian winter temperatures remains unclear. This study reveals that since the early 2000s, East Asia has experienced a strengthening of Aleutian low (AL) and Siberian high (SH) during negative PDO phases, leading to an intensified East Asian winter monsoon (EAWM). The increased pressure gradient between the SH and the AL, driven by warming in the western Pacific associated with the negative PDO phase, has significantly contributed to a shift toward cooling in East Asia (105°–150° E, 20°–50° N) since the early 2000s. Observations and model simulations provide evidence that the enhanced tropical convection in the western Pacific under a negative PDO phase has intensified the atmospheric circulations associated with the EAWM since the early 2000s. Understanding these dynamics is crucial for improving winter temperature forecasts in East Asia.
... Numerous studies have illustrated that the winter AO has considerable impacts on simultaneous weather/climate in the Eurasia and North America (Shabbar & Bonsal, 2004;Thompson & Wallace, 1998), including cold surges (Jeong & Ho, 2005; T. W. Park et al., 2011), surface air temperature (SAT; Woo et al., 2015;, East Asian winter monsoon (D. Y. Gong et al., 2001;He, 2013) and winter precipitation (D. ...
... The weakening in circumpolar westerlies facilitate the movement of cold air from the Arctic to downstream areas, leading to cooling SAT anomalies (Kolstad et al., 2010;Woo et al., 2015) and prolonged cold surge events (T. W. Park et al., 2011;H. Park et al., 2013) across the Eurasian continent. ...
... ). Previous studies have demonstrated the prominent relations of winter AO with simultaneous Eurasian SAT (D. Y.Gong & Wang, 2003; H. N. Gong, Wang, & Chen, 2019 T. W.Park et al., 2011). The results in this study suggested that the late-winter AO could be a predominant contributor to the following early spring SAT predictability at North and Northeast Asia after the 1990s. ...
Numerous studies have highlighted the simultaneous relationship between the Arctic Oscillation (AO) and weather/climate in Asia. However, the stability of the precursor signals in AO for Asian surface air temperature (SAT), which is important for short‐term climate prediction, has received little attention. In this study, a strengthened relationship is identified between the late‐winter AO and the early spring SAT over North and Northeast Asia (NNA) around the 1990s. During 1990–2022, a positive (negative) phase of AO during late winter is generally followed by significant warming (cooling) anomalies in the NNA during early spring, whereas this relationship is insignificant during 1961–1987. Further result shows a good persistence of the late‐winter AO to early spring after the 1990s. Accordingly, the AO exerts a strengthened impact on Mongolian anticyclone and Asian westerly anomalies through modulation of a Rossby wave train that propagates from the Arctic to the NNA in early spring, leading to significant SAT anomalies at NNA. Additionally, the AO‐related temperature anomalies intensified in the stratosphere after the 1990s, linking AO and stratospheric polar vortex (SPV). The intensified (weakened) SPV following positive (negative) AO facilitates warming (cooling) anomalies at NNA via downward‐propagating Eliassen‐Palm fluxes at wave number 1 and circumpolar westerlies in middle and lower troposphere. The seasonal persistence of AO and the strengthened relationship between AO and SPV synergistically enhance the influence of late‐winter AO on early spring SAT in the NNA, which might be attributed to the interdecadal changes in background circulation over the Arctic.
... et al., 2002G. Gong et al., , 2003aG. Gong et al., , 2003b. On interannual timescales, Simmonds et al. (2008) have found that the AO correlates with the frequency of Arctic cyclones. Beyond the low-frequency timescale variations of the AO driven by external forcing, high-frequency timescale events, such as East Asian cold surges (Jeong & Ho, 2005;T. W. Park et al., 2011;Woo et al., 2012), extreme heat events in the U.S. (Higgins et al., 2002;Lim & Schubert, 2011;Wettstein & Mearns, 2002), and extreme precipitation in China (Mao et al., 2011), have also been shown to be closely related to the AO. However, the specific spatiotemporal evolution and mechanisms of the AO on high-frequency timescales remains ...
Plain Language Summary
The Arctic Oscillation (AO) plays an important role in the variability of weather and climate across the entire Northern Hemisphere. This study investigates the correlation between the numbers of extratropical cyclones entering and leaving the Arctic and the AO synoptic variability. The value of the NCF in the North Atlantic region minus that in the North America region is defined as the Joint Net Cyclone Flux (JNCF) which is significantly correlated with the AO synoptic variability with a correlation coefficient of 0.32. The composites of SLP relative to the JNCF index manifest as AO‐like anomalies. Piecewise potential vorticity (PV) inversion results further reveal the quantitative forcing of extra‐tropical cyclones on the synoptic‐scale AO‐like geopotential height anomalies at different altitudes. The effects of extratropical cyclones are more important than Arctic stratospheric PV intrusions. Furthermore, the upper‐level dynamic processes among all extratropical cyclone effects dominate the evolution of synoptic‐scale AO‐like geopotential height anomalies, whereas the mid‐troposphere latent heat release contributes little. Interestingly, the effects of the lower‐troposphere static stability and baroclinicity on the AO‐like synoptic anomalies are completely opposite between the western and eastern parts of the North Atlantic‐Arctic sector.
... In the Southern Hemisphere, blocks are analogously defined as cyclonic rather than anti-cyclonic air masses. This trapping of air parcels inhibits regular atmospheric flow and can result in increased and prolonged extreme heat, 20-23 extreme cold, 21,[24][25][26] or reduced air quality through increased concentration of pollutants. 25,27,28 Despite this phenomenon being conceptualized decades ago, 29,30 much is still not known about the underlying physics behind blocks. ...
Macroscopic features of dynamical systems such as almost-invariant sets and coherent sets provide crucial high-level information on how the dynamics organizes phase space. We introduce a method to identify time-parameterized families of almost-invariant sets in time-dependent dynamical systems, as well as the families’ emergence and disappearance. In contrast to coherent sets, which may freely move about in phase space over time, our technique focuses on families of metastable sets that are quasi-stationary in space. Our straightforward approach extends successful transfer operator methods for almost-invariant sets to time-dependent dynamics and utilizes the Ulam scheme for the generator of the transfer operator on a time-expanded domain. The new methodology is illustrated with an idealized fluid flow and with atmospheric velocity data. We identify atmospheric blocking events in the 2003 European heatwave and compare our technique to existing geophysical methods of blocking diagnosis.
... When the disturbance originating from Euro-Atlantic propagates along the EU teleconnection to East Asia, the East Asian trough in the middle troposphere will be deepened and the surface Siberian high will be intensified (Bueh et al. 2011;Joung and Hitchman 1982;Park et al. 2014;Pang and Lu 2019;Song and Wu 2017;Nakamura 2005a, 2005b;Wang et al. 2010;Wang and Lu 2017;Wang and Zhang 2014). These result in a strong East Asian winter monsoon (EAWM) and a southward invasion of cold air mass to the lower latitudes, decreasing the surface temperature over East Asia (Leung et al. 2017;Park et al. 2011;Song and Wu 2017). Low temperature and precipitation are observed over China during the decaying stage of EU teleconnection, typically 2-4 days lagging the peak phase of teleconnection (Wang and Zhang 2014). ...
In February 2022, an extreme wet and cold event hits South China, with the regional precipitation ranking the second highest record, while the temperature ranking the third lowest since 1979. In this study, the physical mechanisms of this extreme event are investigated from the perspective of multiple timescales interaction. Results show that the strong confrontation between the warm and moist air advection by the India-Burma trough (IBT) and the invasion of cold air activity related to strengthening of the East Asian winter monsoon (EAWM) is the key to trigger this extreme event. Further analyses show that the multi-timescale coupling of the South Asian jet wave train and Eurasian (EU) teleconnection is the main reason for the strong cold and warm-moist air flow. The EU teleconnection on both intraseasonal and synoptic timescales plays a key role in triggering this extreme event by strengthening the EAWM. On synoptic timescale, not only EU teleconnection, but also the South Asian jet wave train plays a key role. They show a stronger intensity on this timescale and their coupling are obvious. The South Asian jet wave train enhances the moisture supply by deepening the IBT, which further conflicts with the strong EAWM modulated by EU teleconnection over South China, leading to this extreme wet-cold event. The forecast skills in the Subseasonal to Seasonal (S2S) prediction project models of this event are evaluated in this paper, results show that the ECMWF model can successfully predict the extreme precipitation by capturing the coupling of the two wave trains with a 5 days lead time.
... For identification and quantification of atmospheric circulations, classification methods are often applied. Atmospheric circulations associated with cold surges were grouped into wave train and blocking categories (Park et al. 2011). The blocking types over the NH can be further classified (Barriopedro and García-Herrera 2006). ...
The ERA5 reanalysis during cold months (November-March) of 1979-2020 was used for determining four cluster centroids through the k-means for classifying regional anomalies of the daily geopotential height at 500 hPa (H500) over northeastern China. EOF was used to reduce dimensionality. Four clusters were linked to the EOF patterns with clear meteorological meanings, which are associated with the evolutions of ridge and trough over northeastern China. Those systems relate to warm and cold advections at 850 hPa. In each H500 cluster, the advection is the major contributor leading to temperature changes at 850 hPa, which significantly relates to the changes and anomalies of daily minimum air temperature at 2m (T2min). Furthermore, the jet activities over Asia relate to more or less occurrence of specific H500 clusters in jet phases. This is because anomalous westerlies are generally in favor of positive anomalies of vorticity tendency at 500 hPa. For the reforecasts during 2004-2019 in the CMA S2S model, the hit rates above 50% for all the H500 clusters are within 9.5 days, which are in between those for the first two and the last two clusters. The correct prediction of H500 anomalies improves the T2min prediction up to 12 days, compared with 8 days for the incorrect one. The good prediction of the jet activities leads to more accurate prediction of H500 anomalies. Therefore, improvement of the model prediction of the jet activities and the H500 anomalies will lead to better prediction of winter weather near the ground over northeastern China.
... In the Southern Hemisphere, blocks are analogously defined as cyclonic rather than anticyclonic air masses. This trapping of air parcels inhibits regular atmospheric flow and can result in increased and prolonged extreme heat [11,4,12,59], extreme cold [11,6,41,7], or reduced air quality through increased concentration of pollutants [3,63,7]. Despite this phenomenon being conceptualised decades ago [45,46], much is still not known about the underlying physics behind blocks. ...
Macroscopic features of dynamical systems such as almost-invariant sets and coherent sets provide crucial high-level information on how the dynamics organises phase space. We introduce a method to identify time-parameterised families of almost-invariant sets in time-dependent dynamical systems, as well as the families' emergence and disappearance. In contrast to coherent sets, which may freely move about in phase space over time, our technique focuses on families of metastable sets that are quasi-stationary in space. Our straightforward approach extends successful transfer operator methods for almost-invariant sets to time-dependent dynamics and utilises the Ulam scheme for the generator of the transfer operator on a time-expanded domain. The new methodology is illustrated with an idealised fluid flow and with atmospheric velocity data. We identify atmospheric blocking events in the 2003 European heatwave and compare our technique to existing geophysical methods of blocking diagnosis.
... The Arctic Oscillation (AO) is recognized as the primary mode of atmospheric variability in the Northern Hemisphere, impacting weather and climate at mid-high latitudes (Thompson and Wallace 1998). It is particularly influential on boreal winter climates in regions such as North America, Europe, and East Asia (Higgins et al 2002, Kolstad et al 2010, Park et al 2011, Tomassini et al 2012, Kim and Ahn 2015. Extensive studies have explored the variability of the AO and its profound impact not only on air temperature, precipitation, sea ice, snow cover, and the Asian monsoon system (e.g. ...
Although the seasonal prediction skill of climate models has improved significantly in recent decades, the prediction skill of the Arctic Oscillation (AO), the dominant climate mode over the Northern Hemisphere, remains poor. Additionally, the local representation of AO impacts has diverged from observations, which limits seasonal prediction skill of climate models. In this study, we attempted to improve prediction skill of surface air temperature (SAT) with two post-processing on dynamical model’s seasonal forecast: (1) correction of the AO impact on SAT pattern, and (2) correction of AO index (AOI). The first correction involved replacing the inaccurately simulated impact of AO on SAT with that observed. For the second correction, we employed a empirical prediction model of AOI based on multiple linear regression model based on three precursors: summer sea surface temperature, autumn sea-ice concentration, and autumn snow cover extent. The application of the first correction led to a decrease in prediction skills. However, a significant improvement in SAT prediction skills is achieved when both corrections are applied. The average correlation coefficients for the North America and Eurasian regions increased from 0.23 and 0.06 to 0.28 and 0.30, respectively.
... This indicates that Asia may experience the CAOs that are characterized by cold anomalies invaded southward during the 2-3 weeks before the SNAMpeak. The related synoptic features as shown in Fig. S1 resemble those found in the blocking-type CAOs over East Asia that tend to occur during the negative AO periods (Ding 1990;Cheung et al. 2012;Cohen et al. 2012;Park et al. 2011;Woo et al. 2015) and the persistent Eurasian cold events accompanied with SSW (Finke et al. 2023;Zhang et al. 2023). In contrast, most regions of the North American continent are anomalously warm, as indicated by the significantly positive T 2m anomalies in phase 0 ~ 10 and 16 ~ 20 of SNAM - (Fig. 5a-d) and negative values of NA_PC1 in phase 0 ~ 6 and 17 ~ 18 of SNAM - (Fig. 6c). ...
... This period corresponds to the 1 month after a stronger polar vortex. The features in the synoptic systems resemble those associated with the wave-train type CAOs over East Asia, whose wave train features are relatively stronger under the background of positive AO than negative AO (Lau and Lau 1984;Park et al. 2011;. ...
... Because the AO is significantly negative in phase 20 ~ 35 (about 0d ~ + 30d after the peak) of SNAM -, the related circulation pattern is favorable for the westward cold air intrusion into Europe according to Walsh et al. (2001), explaining the CAOs over Europe at the decaying stage of SNAM -. Then, because the AO turns to be significantly positive in phase 17 ~ 31 (about -3d ~ + 22d after the peak) of SNAM + , the related circulation pattern is always related to the wave-train type CAOs over Asia according to Park et al. (2011; and Finke et al. (2023), explaining the features of CAOs over Asia at the decaying stage of SNAM + . ...
A Stratospheric Northern Annular Mode (SNAM) phase-based composite analysis reveals that continental Cold Air Outbreaks (CAOs) can occur during both positive and negative SNAM events. CAOs tend to occur over Asia, characterized by a meridional-dipole surface temperature anomaly pattern (cold midlatitudes and warm high-latitudes) when the SNAM index is decreasing or the stratospheric polar vortex is weakening, but over North America and Europe with a meridionally-homogeneous pattern when the SNAM index is increasing or the stratospheric polar vortex is strengthening. While the decreasing SNAM is dominated by a stronger stratospheric poleward warm branch (WB-ST) of the isentropic meridional mass circulation and vice versa, the CAOs always follow a stronger tropospheric poleward warm branch (WB-TR) and an equatorward cold branch (CB) of the isentropic meridional mass circulation. The correspondence between the stronger/weaker WB-ST and stronger/weaker WB-TR&CB during majority of SNAM phases (referred to as stratosphere-troposphere coupling regimes) is responsible for the CAOs in Asia. During the remaining phases (stratosphere-troposphere decoupling regimes), in accompany with a weaker/stronger WB-ST, the WB-TR&CB are stronger/weaker and relates to the CAOs occurred in North America and Europe. The coupling regimes when the stratospheric polar vortex is weakening/strengthening are mainly attributed to the E-P flux convergence/divergence from the middle troposphere to the lower stratosphere, the larger wave amplitude throughout the column, and anomalous tropospheric wave flux mainly in the Asia in subpolar latitudes. The decoupling regimes, however, are mainly related to the anomalous westward-tilting of waves and the wave flux reflection toward the North America or Europe.
