scholarly journals Decadal Change of the Western North Pacific Summer Monsoon Break around 2002/03

2017 ◽  
Vol 31 (1) ◽  
pp. 177-193 ◽  
Author(s):  
Ke Xu ◽  
Riyu Lu
Keyword(s):  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Meridional Circulation ◽  
Warm Pool ◽  
Mariana Islands ◽  
Decadal Change ◽  
Pacific Warm Pool ◽  
Break Region ◽  
The Western Pacific

Abstract A significant decadal change is detected in the break of the western North Pacific summer monsoon (WNPSM) around 2002/03. For the period 1979–2002, the monsoon break occurs in early August, accompanied by noticeable convection suppression over the ocean to the east of the Mariana Islands (10°–20°N, 140°–160°E). However, for the period 2003–11, the monsoon break there is delayed until mid-August. This decadal change is attributable to the differences in the evolution of the WNPSM. Over this break region, convection becomes weaker after its peak in late July for the former period, and the monsoon break appears in early August. In contrast, for the latter period, convection continues strengthening in late July and reaches its peak in early August, and the monsoon break is delayed until mid-August. The differences in the evolution of sea surface temperature (SST) in the western Pacific warm pool region are responsible for the decadal change in the evolution of the WNPSM. In contrast to the former period, for the latter period the southern extent of the warm pool is remarkably warmed, and tends to be higher than the northern extent in mid- and late July, which enhances atmospheric convection nearby but inhibits the development of convection over the northern extent through a local meridional circulation. As the SST in the northern extent continues warming and becomes higher than that in the southern extent, the convection over the northern extent reaches its maximum intensification in early August. The presented results highlight that the spatial pattern of SST changes can modulate the subseasonal evolution of the WNPSM.

scholarly journals Change in Tropical Cyclone Activity during the Break of the Western North Pacific Summer Monsoon in Early August

2016 ◽  
Vol 29 (7) ◽  
pp. 2457-2469 ◽  
Author(s):  
Ke Xu ◽  
Riyu Lu
Keyword(s):  
Tropical Cyclone ◽  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Cyclonic Circulation ◽  
Tropical Cyclone Activity ◽  
Upward Motion ◽  
Mariana Islands ◽  
Cyclone Activity

Abstract The modulation of tropical cyclone (TC) activity by the western North Pacific (WNP) monsoon break is investigated by analyzing the subseasonal evolution of TCs and corresponding circulations, based on 65 years of data from 1950 to 2014. The monsoon break has been identified as occurring over the WNP in early August. The present results show that TC occurrence decreases (increases) remarkably to the east of the Mariana Islands (southeast of Japan) during the monsoon break, which is closely related to local anomalous midtropospheric downward (upward) motion and lower-tropospheric anticyclonic (cyclonic) circulation, in comparison with the previous and subsequent convective periods in late July and mid-August. These changes of TC activity and the corresponding circulation during the monsoon break are more significant in typical monsoon break years when the monsoon break phenomenon is predominant. The reverse changes of TC activity to the east of the Mariana Islands and to the southeast of Japan during the monsoon break are closely associated with the out-of-phase subseasonal evolutions over these two regions from late July to mid-August, which are both contributed to greatly by 10–25-day oscillations. Finally, the roles of midlatitude and tropical disturbances on 10–25-day oscillations are also discussed.

scholarly journals Sub-seasonal variations of the tropical storm track in the western north Pacific

MAUSAM ◽  
2021 ◽  
Vol 48 (2) ◽  
pp. 189-194
Author(s):  
BIN WANG ◽  
LIGUANG WU
Keyword(s):  
Summer Monsoon ◽  
Seasonal Variations ◽  
North Pacific ◽  
Time Scale ◽  
Western North Pacific ◽  
Storm Track ◽  
Tropical Storm ◽  
Climatological Data ◽  
Seasonal Oscillation ◽  
The Western Pacific

 With 20-year (1975-94) climatological data, we demonstrate that the tropical storm track over the western North Pacific (0° - 40°N, 100 - 180°E) exhibits prominent sub-seasonal variations on a time scale of about 40 days from May to November. The storm track variability is regulated by the conspicuous Climatological Intra Seasonal Oscillation (CISO) in the strength of the western North Pacific summer monsoon and the associated position of the western Pacific Sub-tropical High. The CISO cycle regulates the number of tropical storm formation during the Pre-Onset and Withdraw Cycles but not during the Onset and Peak Monsoon Cycles (from mid-June to mid-September).    

Meridional SST gradient in the western North Pacific warm pool associated with typhoon generation

2008 ◽  
Vol 35 (12) ◽  
pp. n/a-n/a ◽  
Author(s):  
N. Sato ◽  
R. Shirooka ◽  
M. Yoshizaki ◽  
Y. N. Takayabu
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Warm Pool ◽  
Pacific Warm Pool ◽  
Sst Gradient ◽  
Meridional Sst Gradient

scholarly journals Influence of Tropical SSTs on the Interannual Variation of the Summer Monsoon Break over the Western North Pacific

2019 ◽  
Vol 32 (10) ◽  
pp. 2807-2821 ◽  
Author(s):  
Ke Xu ◽  
Riyu Lu ◽  
Baek-Jo Kim ◽  
Jiangyu Mao ◽  
Jong-Kil Park
Keyword(s):  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Interannual Variation ◽  
Mariana Islands ◽  
Local Wind ◽  
Tropical Ssts ◽  
Strong Convection ◽  
Phase Out ◽  
Sst Anomalies

Abstract The break of the western North Pacific (WNP) summer monsoon (WNPSM) occurs climatologically in early August and is accompanied by a remarkable suppression of convection over the ocean east of the Mariana Islands (10°–20°N, 140°–160°E). This suppression of convection is sandwiched between two convection peaks in late July and mid-August. Two types of monsoon break are identified in the interannual variation of the WNPSM break in the period 1979–2015, exhibiting a distinct subseasonal evolution of convection that is either in phase or out of phase with the climatological evolution. The preceding SST anomalies in the tropical WNP during early and mid-July are responsible for the interannual variation of the monsoon break. Warm (cold) SST anomalies induce an advanced (delayed) evolution of the WNPSM, with the establishment of strong convection in late July (early August) followed by a monsoon break in early August (mid-August). The subseasonal evolution of convection is therefore in phase (out of phase) with that of the climatological mean. The above SST anomalies mainly result from the local wind–evaporation–SST positive feedback during spring and summer. This local air–sea interaction is still robust after the linear regression components related to the variability of ENSO are excluded from the original fields, indicating that it is, to a large extent, independent of ENSO. The ENSO decaying phases have a secondary role in modulating the SST anomalies related to the WNPSM break.

Impacts of the Boreal Spring Indo-Pacific Warm Pool Hadley Circulation on Tropical Cyclone Activity over the Western North Pacific

2018 ◽  
Vol 31 (4) ◽  
pp. 1361-1375 ◽  
Author(s):  
Yi-Peng Guo ◽  
Zhe-Min Tan
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
North Pacific ◽  
Western North Pacific ◽  
Hadley Circulation ◽  
Warm Pool ◽  
Westerly Wind ◽  
Pacific Warm Pool ◽  
Sst Gradient

This study investigated the impacts of the interannual variability in the boreal spring regional Hadley circulation over the Indo-Pacific warm pool (IPWP) on the tropical cyclone (TC) activity over the western North Pacific (WNP). The principal modes of the interannual variability in the IPWP Hadley circulation were calculated using empirical orthogonal function (EOF) analysis. The leading mode (EOF-1) features cross-equatorial southerly wind anomalies over the Indian Ocean and Maritime Continent and has an evident impact on WNP TC activity during summer. In the summer following a positive phase of the EOF-1, a cyclonic circulation anomaly, with upward motion, positive relative vorticity anomalies, and weak sea level pressure, dominates the WNP, and this favors increased TC genesis. However, large positive vertical wind shear anomalies over the South China Sea and Philippine Sea inhibit the TC intensification. A positive wind–sea surface temperature (SST)–precipitation feedback was found to facilitate the ability of the signal of the EOF-1 to persist until the summer. The westerly wind anomalies converge around 10°N over the WNP, thus increasing precipitation, and this increased precipitation enhances the westerly wind anomalies via a Gill-type response. The strengthened westerly wind anomalies increase total wind speeds, which in turn cool the SST in the Bay of Bengal and the South China Sea, and warm the SST in the eastern WNP, increasing the zonal SST gradient. Consequently, this increased zonal SST gradient further enhances the westerly wind anomalies, strengthens the monsoon trough, and increases the WNP precipitation further. Therefore, the WNP precipitation anomalies are sustained into the summer.

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