The intensity of the winter Siberian High has significantly negative correlations with Arctic sea ice concentration anomalies from the previous autumn to winter seasons in the Eastern Arctic Ocean and Siberian marginal seas. Our results indicate that autumn-winter Arctic sea ice concentration and concurrent sea surface temperature anomalies are responsible for the winter Siberian High and surface air temperature anomalies over the mid-high latitudes of Eurasia and East Asia. Numerical experiments also support this conclusion, and consistently show that the low sea ice concentration causes negative surface air temperature anomalies over the mid-high latitudes of Eurasia. A mechanism is proposed to explain the association between autumn-winter sea ice concentration and winter Siberian High. Our results also show that September sea ice concentration provides a potential precursor for winter Siberian High that cannot be predicted using only tropical sea surface temperatures. In the last two decades (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)), a strengthening trend of winter Siberian High along with a decline trend in surface air temperature in the mid-high latitudes of the Asian Continent have favored the recent frequent cold winters over East Asia. The reason for these short-term trends in winter Siberian High and surface air temperature are discussed. Arctic sea ice, Siberian High, East Asian climate, frequent cold winterCitation:
The amplitude asymmetry between El Niñ o and La Niñ a is investigated by diagnosing the mixed-layer heat budget during the ENSO developing phase by using the three ocean assimilation products: Simple Ocean Data Assimilation (SODA) 2.0.2, SODA 1.4.2, and the Global Ocean Data Assimilation System (GODAS). It is found that the nonlinear zonal and meridional ocean temperature advections are essential to cause the asymmetry in the far eastern Pacific, whereas the vertical nonlinear advection has the opposite effect. The zonal current anomaly is dominated by the geostrophic current in association with the thermocline depth variation. The meridional current anomaly is primarily attributed to the Ekman current driven by wind stress forcing. The resulting induced anomalous horizontal currents lead to warm nonlinear advection during both El Niñ o and La Niñ a episodes and thus strengthen (weaken) the El Niñ o (La Niñ a) amplitude. The convergence (divergence) of the anomalous geostrophic mixed-layer currents during El Niñ o (La Niñ a) results in anomalous downwelling (upwelling) in the far eastern equatorial Pacific, which leads to a cold nonlinear vertical advection in both warm and cold episodes.
Using NCEP–NCAR reanalysis and Japanese 25-yr Reanalysis (JRA-25) data, this paper investigates the association between winter sea ice concentration (SIC) in Baffin Bay southward to the eastern coast of Newfoundland, and the ensuing summer atmospheric circulation over the mid- to high latitudes of Eurasia. It is found that winter SIC anomalies are significantly correlated with the ensuing summer 500-hPa height anomalies that dynamically correspond to the Eurasian pattern of 850-hPa wind variability and significantly influence summer rainfall variability over northern Eurasia. Spring atmospheric circulation anomalies south of Newfoundland, associated with persistent winter–spring SIC and a horseshoe-like pattern of sea surface temperature (SST) anomalies in the North Atlantic, act as a bridge linking winter SIC and the ensuing summer atmospheric circulation anomalies over northern Eurasia. Indeed, this study only reveals the association based on observations and simple simulation experiments with SIC forcing. The more precise mechanism for this linkage needs to be addressed in future work using numerical simulations with SIC and SST as the external forcings. The results herein have the following implication: Winter SIC west of Greenland is a possible precursor for summer atmospheric circulation and rainfall anomalies over northern Eurasia.
An interannual variability mode in the southeast Pacific with a physical interpretation similar to that of the Pacific meridional mode (PMM) in the North Pacific was recently identified. Both modes have been shown to influence the subsequent development of El Niño–Southern Oscillation (ENSO) events. This study investigates the relationship between ENSO and the two PMMs using observational and reanalysis data. The results show that the South Pacific meridional mode (SPMM) mainly favors the development of sea surface temperature anomalies (SSTAs) in the eastern equatorial Pacific, whereas the North Pacific meridional mode (NPMM) mainly favors the development of SSTAs in the central equatorial Pacific. Both of the meridional modes are considered to be analogous in terms of their physical interpretation and can be important predictors of ENSO when considering different flavors of ENSO. Neither the NPMM nor the SPMM can be precluded as accurate indicators when forecasting particular flavors of ENSO.
At the beginning of 2014, an El Niño event was predicted to occur in the following winter. However, the El Niño that started to develop in 2014 was hindered in the boreal summer, and only the ocean reached a weak El Niño condition. This outcome was largely attributed to a suppressed ocean‐atmosphere interaction caused by anomalous easterly winds in the eastern equatorial Pacific. These winds were related to negative sea surface temperature anomalies (SSTAs) in the southeastern subtropical Pacific (SESP). The negative phase of the Interdecadal Pacific Oscillation (IPO) laid the foundation for the persistence of cooler SSTAs and enhanced trade winds in the SESP after the year 2000. As the recent IPO downward trend continued, the SSTAs in SESP reached an extremely low value in the boreal summer of 2014 and imposed a serious obstacle to the evolution of a warming event.
23This paper describes two dominant patterns of Asian winter climate variability: the 24 Siberian high (SH) pattern and the Asia-Arctic (AA) pattern. The former depicts atmospheric 25 variability closely associated with the intensity of the Siberian high, and the latter 26 characterizes the teleconnection pattern of atmospheric variability between Asia and the 27 Arctic, which is distinct from the Arctic Oscillation (AO). The AA pattern plays more 28 important roles in regulating winter precipitation and the 850 hPa meridional wind component 29 over East Asia than the SH pattern, which controls surface air temperature variability over 30 East Asia. 31 In the Arctic Ocean and its marginal seas, sea ice loss in both autumn and winter could 32 bring the positive phase of the SH pattern, or cause the negative phase of the AA pattern. The 33 latter corresponds to a weakened East Asian winter monsoon (EAWM) and enhanced winter 34 precipitation in the mid-latitudes of the Asian continent and East Asia. For the SH pattern, sea 35 ice loss in the prior autumn emerges in the Siberian marginal seas, and winter loss mainly 36 occurs in the Barents Sea, Labrador Sea, and Davis Strait. For the AA pattern, sea ice loss in 37 the prior autumn is observed in the Barents-Kara Seas, the western Laptev Sea, and the 38 Beaufort Sea, and winter loss only occurs in some areas of the Barents Sea, the Labrador Sea, 39 and Davis Strait. Simulation experiments with observed sea ice forcing also support that 40 Arctic sea ice loss may favor frequent occurrence of the negative phase of the AA pattern. The 41 results also imply that the relationship between Arctic sea ice loss and winter atmospheric 42 variability over East Asia is unstable, which is a challenge for predicting the EAWM based on 43 Arctic sea ice loss.44 3
The northward shift of the Western North Pacific Subtropical High (WNPSH) in July 2018 broke the historical record since 1958 and resulted in extreme heat waves and casualties across Northeast Asia (NEA). In the present work, we associated this extreme WNPSH anomaly with the anomalies of barotropic anticyclone above NEA originating from the strongest positive tripole pattern of sea surface temperature anomaly (SSTA) in the North Atlantic in July. Both data analysis and numerical experiments indicated that the positive tripole SSTA pattern could produce an upper-tropospheric wave source over Europe, which stimulated an eastward propagating wave train along the subpolar westerly jet over the Eurasian Continent. When its anticyclonic node reached NEA, the WNPSH started to shift northward. After the cyclonic node in the circulation anomaly encountered the Tibetan Plateau (TP), atmospheric diabatic heating was enhanced over the eastern TP, initiating another subtropical wave train, which furthered the northward shift of the WNPSH. Therefore, the wave source over Europe was critical for the northward shift of the WNPSH in July, connecting the tripole SSTA pattern in the North Atlantic with the WNPSH anomaly and maintaining the downstream effects of thermal forcing over the eastern TP on the East Asian summer monsoon.
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