Dynamic effect of the South Asian high on the interannual zonal extension of the western North Pacific subtropical high

2019 ◽  
Vol 39 (14) ◽  
pp. 5367-5379 ◽  
Author(s):  
Wei Wei ◽  
Renhe Zhang ◽  
Min Wen ◽  
Song Yang ◽  
Wenhong Li
Keyword(s):  
South Asian ◽  
North Pacific ◽  
Western North Pacific ◽  
Dynamic Effect ◽  
Subtropical High ◽  
South Asian High ◽  
The South

scholarly journals Upper-Tropospheric Forcing on Late July Monsoon Transition in East Asia and the Western North Pacific

2012 ◽  
Vol 25 (11) ◽  
pp. 3929-3941 ◽  
Author(s):  
Chi-Hua Wu ◽  
Ming-Dah Chou
Keyword(s):  
East Asia ◽  
South Asian ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Asian Monsoon ◽  
Monsoon Circulation ◽  
South Asian Monsoon ◽  
The South ◽  
The North

By investigating the large-scale circulation in the upper troposphere, it is demonstrated that the rapid late July summer monsoon transition in the East Asia and western North Pacific (EA-WNP) is associated with a weakened westerly at the exit of the East Asian jet stream (EAJS). Even in a normally stable atmosphere under the influence of the North Pacific (NP) high in late July, convection rapidly develops over the midoceanic region of the western NP (15°–25°N, 150°–170°E). Prior to the rapid transition, the EAJS weakens and shifts northward, which induces a series of changes in downstream regions; the northeastern stretch of the Asian high weakens, upper-tropospheric divergence in the region southwest of the mid-NP trough increases, and convection is enhanced. At the monsoon transition, upper-level high potential vorticity intrudes southward and westward, convection expand from the mid NP westward to cover the entire subtropical western NP, the lower-tropospheric monsoon trough deepens, surface southwesterly flow strengthens, and the western stretch of the NP high shifts northward ~10° latitude to the south of Japan. This series of changes indicates that the EA-WNP late July monsoon transition is initiated from changes in the upper-tropospheric circulation via the weakening of the EAJS south of ~45°N. The weakening of the EAJS south of ~45°N is related to a reduced gradient of the geopotential height on the northern flank of the Asian high, which is related to the massive inland heating and weakening of the South Asian monsoon circulation. The exact timing of the monsoon onset might be tied to the hypothesized “Silk Road pattern” and/or a strong weakening of the South Asian monsoon circulation.

A Recent Increase in Long-Lived Heatwaves in China Under the Joint Influence of South Asia and Western North Pacific Subtropical Highs

2021 ◽  
pp. 1-42
Author(s):  
Na LI ◽  
Ziniu XIAO ◽  
Liang ZHAO
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Regional Climate ◽  
Climate Extremes ◽  
Kendall Test ◽  
Subtropical High ◽  
South Asian High ◽  
The Tibetan Plateau ◽  
Synergy Index

AbstractLong-lived (≥6 days) heatwaves (HWs) have strong social impacts with serious health implications. Using homogenized historical daily temperatures from China and ECMWF reanalysis data, this study investigates its frequency between 1979 and 2018 and driving mechanisms. It is found that the occurrence of HWs is strongly associated with the joint actions of the South Asian high and the western North Pacific subtropical high, which can be described by a synergy index measured by the boundary distance between the two subtropical high-pressure systems. When the synergy index is positive, there are more long-lived HWs occurrence in the east of the Tibetan Plateau, the lower reaches of the Yangtze River and the southern region in China, and vice versa. A Mann-Kendall test shows a significant interdecadal shift around 2004/2005 towards increased occurrence that is consistent with enhanced subtropical high systems. This study shows the important roles of large-scale dynamic systems in regional climate extremes and their future changes.

scholarly journals Connection between Anomalous Zonal Activities of the South Asian High and Eurasian Summer Climate Anomalies

2016 ◽  
Vol 29 (22) ◽  
pp. 8249-8267 ◽  
Author(s):  
Jian Shi ◽  
Weihong Qian
Keyword(s):  
South Asian ◽  
Surface Air Temperature ◽  
Northern China ◽  
Boreal Summer ◽  
South Asian High ◽  
The South ◽  
Climate Anomalies ◽  
Precipitation Anomalies ◽  
Air Column ◽  
Air Temperature Anomalies

Abstract Using the daily mean anomalies of atmospheric variables from the NCEP Reanalysis-1 (NCEP R1), this study reveals the connection between anomalous zonal activities of the South Asian high (SAH) and Eurasian climate anomalies in boreal summer. An analysis of variance identifies two major domains with larger geopotential height variability located in the eastern and western flanks of the SAH at around 100 and 150 hPa, respectively. For both eastern and western domains, extreme events are selected during 1981–2014 when normalized height anomalies are greater than 1.0 (less than −1.0) standard deviation for at least 10 consecutive days. Based on these events, four SAH modes that include strong and weak Tibetan modes (STM and WTM, respectively) and strong and weak Iranian modes (SIM and WIM, respectively) are defined to depict the zonal SAH features. The positive composite in the eastern (western) domain indicates the STM (SIM) manifests a robust wavelike pattern with an anomalous low at 150 hPa, and surface cold and wet anomalies over Mongolia and northern China (Kazakhstan and western Siberia) are surrounded by three anomalous highs at 150 hPa and surface warm and dry anomalies over Eurasia. Opposite distributions are also evident in the negative composites of the two domains (WTM and WIM). The surface air temperature anomalies are the downward extension of an anomalous air column aloft while the precipitation anomalies are directly associated with the height anomalies above the air column.

scholarly journals Interannual and interdecadal impact of Western North Pacific Subtropical High on tropical cyclone activity

2020 ◽  
Vol 54 (3-4) ◽  
pp. 2237-2248 ◽  
Author(s):  
Qiong Wu ◽  
Xiaochun Wang ◽  
Li Tao
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Southern Oscillation ◽  
Subtropical High ◽  
Interdecadal Change ◽  
Steering Flow ◽  
The Pacific ◽  
Sea Surface Temperature Anomalies ◽  
Peak Phase

AbstractIn this study, we analyzed the impacts of Western North Pacific Subtropical High (WNPSH) on tropical cyclone (TC) activity on both interannual and interdecadal timescales. Based on a clustering analysis method, we grouped TCs in the Western North Pacific into three clusters according to their track patterns. We mainly focus on Cluster 1 (C1) TCs in this work, which is characterized by forming north of 15° N and moving northward. On interannual timescale, the number of C1 TCs is influenced by the intensity variability of the WNPSH, which is represented by the first Empirical Orthogonal Function (EOF) of 850 hPa geopotential height of the region. The WNPSH itself is modulated by the El Niño–Southern Oscillation at its peak phase in the previous winter, as well as Indian and Atlantic Ocean sea surface temperature anomalies in following seasons. The second EOF mode shows the interdecadal change of WNPSH intensity. The interdecadal variability of WNPSH intensity related to the Pacific climate regime shift could cause anomalies of the steering flow, and lead to the longitudinal shift of C1 TC track. Negative phases of interdecadal Pacific oscillation are associated with easterly anomaly of steering flow, westward shift of C1 TC track, and large TC impact on the East Asia coastal area.

scholarly journals Effect of Warm SST in the Subtropical Eastern North Pacific on Triggering the Abrupt Change of the Mei-Yu Rainfall over South China in the Early 1990s

2020 ◽  
Vol 33 (2) ◽  
pp. 657-673
Author(s):  
Yi-Kai Wu ◽  
An-Yi Huang ◽  
Chia-Kai Wu ◽  
Chi-Cherng Hong ◽  
Chi-Chun Chang
Keyword(s):  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Abrupt Change ◽  
Phase Relationship ◽  
Summer Rainfall ◽  
Boreal Summer ◽  
The South ◽  
Abrupt Increase ◽  
Huaihe River Valley

AbstractIn the early 1990s, the mei-yu rainfall over South China in early boreal summer exhibited an abrupt change and northward extension. This change altered the pattern of East Asian summer rainfall from a dipole-like to a monopole-like pattern; that is, the out-of-phase relationship between the rainfall in the south and that in the north of the Yangtze and Huaihe River valley changed to an in-phase relationship. The physical processes potentially responsible for triggering this abrupt change were analyzed in this study. Our observations revealed that the western North Pacific subtropical high (WNPSH), sea surface temperature (SST) in the subtropical eastern North Pacific (SENP), and the mei-yu rainfall in South China exhibited an abrupt increase in the early 1990s, suggesting that these factors are correlated. From the observations and results of numerical experiments, we proposed that the abrupt SST warming in the SENP in the early 1990s generated an east–west overturning circulation anomaly in the Pacific Ocean and that the anomalous downward motion in the western North Pacific consequently triggered the abrupt increase and westward extension of the WNPSH in the early 1990s. The enhanced and westward extension of WNPSH created a low-level southeasterly anomaly that transported considerable humid and warm air into East Asia and sequentially triggered the abrupt increase of mei-yu rainfall in the South China in the early 1990s.

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