Search Results (4)

Based on observation data from 1958 to 2020, the current study explores the interdecadal modulation effects on moderate El Niño-Southern Oscillation (ENSO) episodes and East Asian (EA) winter surface air temperature (SAT) through the Pacific Decadal Oscillation (PDO). Strong and moderate ENSO episodes are classified by their amplitudes. The current work investigates the influence of moderate ENSO episodes on the EA winter SAT, especially moderate La Niña episodes, which show a close relationship with the EA winter SAT. To explore the PDO modulation effect on the influence of ENSO episodes, these ENSO episodes are further divided into two categories in terms of warm or cold PDO phases. The composite results show that in the warm phase of the PDO, the moderate La Niña signal is relatively strong and stable, with a profound impact on the EA winter SAT variability, whereas in the cold PDO phase, the relationship between the EA winter SAT and moderate La Niña episodes becomes ambiguous. Further studies show that the PDO modulates the moderate La Niña impacts on EA winter SAT primarily through varying the East Asian winter monsoon (EAWM). While moderate La Niña episodes take place in a warm PDO phase, positive and negative anomalies of sea level pressure (SLP) are observed in the Eurasian continent and mid–high-latitude North Pacific, respectively, favoring anomalous northerlies along the eastern coast of East Asia and therefore a colder-than-normal EA winter. In contrast, in a moderate La Niña winter during the cold PDO phase, the mid–high-latitude North Pacific is controlled by an anomalous high-pressure system with southerly anomalies along its western flank, and therefore, a weak warm pattern is observed for the EA winter SAT. Full article

Despite progressing global warming, extreme cold events in East Asia are still occurring frequently with temperature variability enhanced. To understand this situation, it is necessary to determine external and internal climatic factors and their modulation effects that influence regional temperature variability. We found that the positive correlation between Arctic Oscillation (AO) and surface air temperature (SAT) in South Korea during winter is modulated strongly by tropical influences associated with El Niño Southern Oscillation (ENSO). In the case of a negative (positive) SAT anomaly in South Korea during the positive (negative) AO phase, a state that is opposite to the typical relationship between AO and SAT, the tropical sea surface temperature shows a typical negative (positive) ENSO-like pattern. The atmospheric teleconnection associated with the negative (positive) ENSO conditions contributes to a deepening (flattening) of the climatological East Asian trough and an enhancing (weakening) of the East Asian jet, which leads to negative (positive) SAT anomalies in South Korea. This modulation effect is robustly observed in the historical simulations of three different models of CMIP5. Full article

A previous study indicated that the Arctic Oscillation (AO) and Siberian High (SH) are two important drivers for the interannual variation of winter surface air temperature (SAT) over southeast Asia. This study reveals that the impact of the winter SH on the southeast Asian SAT was stable. By contrast, the connection between the winter AO and southeast Asian SAT displays a pronounced interdecadal change around the late-1990s. Significant impact of the winter AO on the southeast Asian SAT can only be detected after the late-1990s. The result shows that change in the impact of the winter AO on southeast Asian SAT was mainly attributed to change in the spatial structure of the AO. Before the late-1990s, significant atmospheric signals related to the winter AO were confined to the North Atlantic region and the atmospheric anomalies over Eurasia were weak. As such, impact of the winter AO on the southeast Asian SAT was weak. By contrast, after the late-1990s, winter AO displays a more zonally symmetric structure, with significant negative sea level pressure (SLP) anomalies over the Arctic, and positive anomalies over mid-latitudes. Specifically, the positive SLP anomalies over East China induce clear northerly wind anomalies over southeast Asia, which lead to negative SAT anomalies there via wind-induced temperature advection. Hence, the winter AO has a significant impact on the southeast Asian SAT after the late-1990s. Further analysis shows that after the late-1990s, hindcast skill of the winter southeast Asian SAT anomalies was enhanced when taking both the winter AO and SH into account. Full article

The occurrence of wintertime cold surges (CSs) over East Asia is largely controlled by the surface air temperature (SAT) distribution at high latitudes and thermal advection in the lower troposphere. The thermodynamic background state over northeastern Asia is associated with the strength of the East Asian winter monsoon and the variation of Arctic Oscillation. This study assesses the importance of the SAT structure with thermal advection in determining the frequency of CS occurrences over East Asia through the analysis of nine atmosphere–ocean coupled global climate models participating in the Coupled Model Intercomparison Project Phase 5. The historical simulations can reproduce the observed typical characteristics of CS development. On the basis of this model performance, ensemble-averaged future simulations under the representative concentration pathway 8.5 project a reduction in CS frequency by 1.1 yr⁻¹ in the late 21st century (2065–2095) compared to the present-day period (1975–2005). The major reason for less frequent CSs in the future is the weakened cold advection, caused by notable SAT warming over the northern part of East Asia. These results suggest that changes in the meridional SAT structure and the associated changes in thermal advection would play a more substantial role than local warming in determining future changes in the frequency of CS occurrences over East Asia. Full article