Interannual Variations of East Asian Trough Axis at 500 hPa and its Association with the East Asian Winter Monsoon Pathway

2009 ◽  
Vol 22 (3) ◽  
pp. 600-614 ◽  
Author(s):  
Lin Wang ◽  
Wen Chen ◽  
Wen Zhou ◽  
Ronghui Huang
Keyword(s):  
East Asia ◽  
North Pacific ◽  
East Asian Winter Monsoon ◽  
Regional Climate ◽  
East Asian ◽  
Winter Monsoon ◽  
Interannual Variations ◽  
Asian Winter Monsoon ◽  
The North ◽  
The North Pacific

Abstract Interannual variations of the East Asian trough (EAT) axis at 500 hPa are studied with the European Centre for Medium-Range Weather Forecasts 40-yr reanalysis data. The associated circulation pattern and pathway of the East Asian winter monsoon (EAWM) with the EAT axis tilt are specially investigated with a trough axis index, which is closely related to the midlatitude baroclinic process and mainly represents the intensity of the eddy-driven jet over the East Asia–North Pacific sector. When the tilt of EAT is smaller than normal, the EAWM prefers to take the southern pathway and less cold air moves to the central North Pacific. However, the EAWM prefers the eastern pathway and brings more cold air to the North Pacific when the tilt of EAT is larger than normal. These differences induce pronounced changes in both the precipitation and the surface air temperature over East and Southeast Asia. Furthermore, the tilt status of the EAT has a significant modulation effect on the regional climate anomalies related to the intensity of the EAWM. The findings suggest an increase in the temperature anomaly associated with the EAWM intensity and a clear northward–southward shift in its pattern in anomalous tilt phase of the EAT. In addition, the modulation tends to be confined mainly to East Asia and expanded to a larger area during the weak and the strong EAWM winters, respectively. The possible reasons for interannual variations of the EAT tilt are discussed, and it is speculated that the midlatitude air–sea interaction in the North Pacific plays a dominant role. This study on the EAT tilt may enrich knowledge of the East Asian winter monsoon beyond the conventional intensity index and may be helpful to improve regional climate prediction in East Asia.

Different Impacts of the East Asian Winter Monsoon on the Surface Air Temperature in North America during ENSO and Neutral ENSO Years

2020 ◽  
Vol 33 (24) ◽  
pp. 10671-10690
Author(s):  
Tianjiao Ma ◽  
Wen Chen ◽  
Hans-F. Graf ◽  
Shuoyi Ding ◽  
Peiqiang Xu ◽  
...  
Keyword(s):  
Wave Packet ◽  
North Pacific ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Surface Air Temperature ◽  
Winter Monsoon ◽  
Asian Winter Monsoon ◽  
The North ◽  
The North Pacific ◽  
Central North Pacific

AbstractThe present study investigates different impacts of the East Asian winter monsoon (EAWM) on surface air temperature (Ts) in North America (NA) during ENSO and neutral ENSO episodes. In neutral ENSO years, the EAWM shows a direct impact on the Ts anomalies in NA on an interannual time scale. Two Rossby wave packets appear over the Eurasian–western Pacific (upstream) and North Pacific–NA (downstream) regions associated with a strong EAWM. Further analysis suggests that the downstream wave packet is caused by reflection of the upstream wave packet over the subtropical western Pacific and amplified over the North Pacific. Also, the East Asian subtropical westerly jet stream (EAJS) is intensified in the central and downstream region over the central North Pacific. Hence, increased barotropic kinetic energy conversion and the interaction between transient eddies and the EAJS tend to maintain the circulation anomaly over the North Pacific. Therefore, a strong EAWM tends to result in warm Ts anomalies in northwestern NA via the downstream wave packet emanating from the central North Pacific toward NA. A weak EAWM tends to induce cold Ts anomalies in western-central NA with a smaller magnitude. However, in ENSO years, an anomalous EAJS is mainly confined over East Asia and does not extend into the central North Pacific. The results confirm that the EAWM has an indirect impact on the Ts anomalies in NA via a modulation of the tropical convection anomalies associated with ENSO. Our results indicate that, for seasonal prediction of Ts anomalies in NA, the influence of the EAWM should be taken into account. It produces different responses in neutral ENSO and in ENSO years.

scholarly journals Regime-Dependent Nonstationary Relationship between the East Asian Winter Monsoon and North Pacific Oscillation

2014 ◽  
Vol 27 (21) ◽  
pp. 8185-8204 ◽  
Author(s):  
Gyundo Pak ◽  
Young-Hyang Park ◽  
Frederic Vivier ◽  
Young-Oh Kwon ◽  
Kyung-Il Chang
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
North Pacific Oscillation ◽  
Asian Winter Monsoon ◽  
The North ◽  
Circulation Patterns ◽  
The North Pacific

Abstract The East Asian winter monsoon (EAWM) and the North Pacific Oscillation (NPO) constitute two outstanding surface atmospheric circulation patterns affecting the winter sea surface temperature (SST) variability in the western North Pacific. The present analyses show the relationship between the EAWM and NPO and their impact on the SST are nonstationary and regime-dependent with a sudden change around 1988. These surface circulation patterns are tightly linked to the upper-level Ural and Kamchatka blockings, respectively. During the 1973–87 strong winter monsoon epoch, the EAWM and NPO were significantly correlated to each other, but their correlation practically vanishes during the 1988–2002 weak winter monsoon epoch. This nonstationary relationship is related to the pronounced decadal weakening of the Siberian high system over the Eurasian continent after the 1988 regime shift as well as the concomitant positive NPO-like dipole change and its eastward migration in tropospheric circulation over the North Pacific. There is a tight tropical–extratropical teleconnection in the western North Pacific in the strong monsoon epoch, which disappears in the weak monsoon epoch when there is a significant eastward shift of tropical influence and enhanced storm tracks into the eastern North Pacific. A tentative mechanism of the nonstationary relationship between the EAWM and NPO is proposed, stressing the pivotal role played in the above teleconnection by a decadal shift of the East Asian trough resulting from the abrupt decline of the EAWM since the late 1980s.

scholarly journals Interdecadal Variations of the East Asian Winter Monsoon in CMIP5 Preindustrial Simulations

2020 ◽  
Vol 33 (2) ◽  
pp. 559-575 ◽  
Author(s):  
Jiapeng Miao ◽  
Tao Wang ◽  
Huijun Wang
Keyword(s):  
North Pacific ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
Climate System ◽  
Asian Winter Monsoon ◽  
The North ◽  
The North Pacific ◽  
Sst Anomalies

AbstractIn this study, focusing on the interdecadal time scale, we investigate the internal variability of the East Asian winter monsoon (EAWM) using output from 19 coupled models’ long-term preindustrial control (piControl) simulations within phase 5 of the Coupled Model Intercomparison Program (CMIP5). In total, we identify 53 cases of significant interdecadal weakening of the EAWM from these 19 piControl simulations. In most weakening cases, both the Siberian high and the East Asian trough are significantly weakened. The East Asian jet stream in the upper troposphere shifts poleward. Southerly wind anomalies are evident over East Asia in the lower troposphere. At the same time, both the Arctic Oscillation (AO) and the North Pacific Oscillation are in their positive phases. Associated anomalous anticyclonic circulation can be found over the North Pacific. Additionally, the North Pacific shows negative Pacific decadal oscillation (PDO)-like sea surface temperature (SST) anomalies. In contrast, we also analyzed 49 cases of significant strengthening of the EAWM, and the atmospheric and oceanic anomalies show opposite signals with the weakening cases. This suggests that internal variabilities of the climate system can also cause interdecadal variations of the EAWM. In addition, the phase shifting of the AO is likely the main reason for the EAWM’s interdecadal variations in the unforced long-term simulations. Further numerical experiments using the Community Atmosphere Model, version 4 (CAM4), deny the causal relationship between the interdecadal variations of EAWM and PDO-like SST anomalies. This study also implies that the internal variabilities of the climate system could contribute to the observed interdecadal weakening of the EAWM around the mid-1980s.

scholarly journals Distinguishing Interannual Variations of the Northern and Southern Modes of the East Asian Winter Monsoon

2014 ◽  
Vol 27 (2) ◽  
pp. 835-851 ◽  
Author(s):  
Zhang Chen ◽  
Renguang Wu ◽  
Wen Chen
Keyword(s):  
Surface Temperature ◽  
North Atlantic ◽  
High Latitude ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
Interannual Variations ◽  
Asian Winter Monsoon ◽  
The North ◽  
The North Atlantic

Abstract The East Asian winter monsoon (EAWM)-related climate anomalies have shown large year-to-year variations in both the intensity and the meridional extent. The present study distinguishes the interannual variations of the low-latitude and mid- to high-latitude components of the EAWM to gain a better understanding of the characteristics and factors for the EAWM variability. Through composite analysis based on two indices representing the northern and southern components (modes) of the EAWM variability, the present study clearly reveals features unique to the northern and southern mode. The northern mode is associated with changes in the mid- to high-latitude circulation systems, including the Siberian high, the Aleutian low, the East Asian trough, and the East Asian westerly jet stream, whereas the southern mode is closely related to circulation changes over the global tropics, the North Atlantic, and North America. A strong northern mode is accompanied by positive, negative, and positive surface temperature anomalies in the Indochina Peninsula, midlatitude Asia, and northeast Russia, respectively. A strong southern mode features lower temperature over tropics and higher temperature over mid- to high-latitude Asia. While the southern mode is closely related to El Niño–Southern Oscillation (ENSO), the northern mode does not show an obvious relation to the tropical sea surface temperature (SST) change or to the North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) on the interannual time scale. Distinct snow cover and sea ice changes appear as responses to wind and surface temperature changes associated with the two modes and their effects on the EAWM variability need to be investigated in the future.

scholarly journals An Intensity Index for the East Asian Winter Monsoon

2014 ◽  
Vol 27 (6) ◽  
pp. 2361-2374 ◽  
Author(s):  
Lin Wang ◽  
Wen Chen
Keyword(s):  
Indian Ocean ◽  
East Asia ◽  
East Asian Winter Monsoon ◽  
Southern Oscillation ◽  
East Asian ◽  
Tropical Indian Ocean ◽  
Winter Monsoon ◽  
The Arctic ◽  
Asian Winter Monsoon ◽  
The North

Abstract The thermal contrast between the Asian continent and the adjacent oceans is the primary aspect of the East Asian winter monsoon (EAWM) that can be well represented in the sea level pressure (SLP) field. Based on this consideration, a new SLP-based index measuring the intensity of the EAWM is proposed by explicitly taking into account both the east–west and the north–south pressure gradients around East Asia. The new index can delineate the EAWM-related circulation anomalies well, including the deepened (shallow) midtropospheric East Asian trough, sharpened and accelerated (widened and decelerated) upper-tropospheric East Asian jet stream, and enhanced (weakened) lower-tropospheric northerly winds in strong (weak) EAWM winters. Compared with previous indices, the new index has a very good performance describing the winter-mean surface air temperature variations over East Asia, especially for the extreme warm or cold winters. The index is strongly correlated with several atmospheric teleconnections including the Arctic Oscillation, the Eurasian pattern, and the North Pacific Oscillation/western Pacific pattern, implying the possible internal dynamics of the EAWM variability. Meanwhile, the index is significantly linked to El Niño–Southern Oscillation (ENSO) and the sea surface temperature (SST) over the tropical Indian Ocean. Moreover, the SST anomalies over the tropical Indian Ocean are more closely related to the index than ENSO as an independent predictor. This adds further knowledge to the prediction potentials of the EAWM apart from ENSO. The predictability of the index is high in the hindcasts of the Centre National de Recherches Météorologiques (CNRM) model from Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction (DEMETER). Hence, it would be a good choice to use this index for the monitoring, prediction, and research of the EAWM.

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