scholarly journals An Analysis of Tropical Cyclone Formations in the South China Sea during the Late Season

2011 ◽  
Vol 139 (9) ◽  
pp. 2748-2760 ◽  
Author(s):  
Yung-Lan Lin ◽  
Cheng-Shang Lee
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
Vertical Wind Shear ◽  
The South China Sea ◽  
The South ◽  
Late Season ◽  
Low Level ◽  
China Sea ◽  
The North

This study examines tropical cyclone (TC) formations in the South China Sea (SCS) associated with the strong northeasterly monsoon during the late season. Results show that the percentage of all vortices that develop to TC intensity is lower in the late season when compared to that associated with the mei-yu front in May and June. But the average formation time for the late-season cases is significantly shorter than that for the mei-yu frontal cases. Composite analyses show that the formation cases in the late season have larger low-level vorticity and upper-level divergence as well as higher 700-hPa relative humidity when compared to the nonformation cases. Another major difference between the formation and the nonformation cases is the low-level northeasterlies to the north (or upstream) of the incipient disturbance, which weakens right before the pre-TC disturbance reaching 25 kt (~13 m s−1). The weakening of the northeasterlies may be important to TC formation because it decreases the vertical wind shear and prevents the shift of the disturbance center from over the southern SCS to near the Borneo landmass. Furthermore, it reduces the stabilizing effect associated with the cold- and dry-air intrusion. Previous studies have shown that stronger equatorial westerlies during the active Madden–Julian oscillation (MJO) period may produce stronger cyclonic shear vorticity; thus, favorable for triggering more convection activities and more vortex formations. However, more vortices or cloud clusters are not necessarily more favorable for an individual vortex to organize into a TC. Nonetheless the initial setup of favorable synoptic environment appears to be important for the further development of the incipient vortex.

scholarly journals Tropical Cyclone Formation within Strong Northeasterly Environments in the South China Sea

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1147
Author(s):  
Yung-Lan Lin ◽  
Hsu-Feng Teng ◽  
Yi-Huan Hsieh ◽  
Cheng-Shang Lee
Keyword(s):  
South China Sea ◽  
South China ◽  
Convective Instability ◽  
Wrf Model ◽  
The South China Sea ◽  
Weather Research And Forecasting ◽  
The South ◽  
Late Season ◽  
Low Level ◽  
China Sea

In the South China Sea (SCS), 17% of tropical cyclones (TCs) formed in the late season (November−January) were associated with a strong northeasterly monsoon. This study explores the effects of northeasterly strength on TC formation over the SCS. The Weather Research and Forecasting (WRF) model is used to simulate the disturbances that develop into TCs (formation cases) and those that do not (non-formation cases). Two formation (29W on 18 November 2001 and Vamei on 26 December 2001) and two non-formation (30 December 2002 and 9 January 2003) cases are simulated. To address the importance of upstream low-level northeasterly strength to TC formation, two types of sensitivity experiments are performed: formation cases with increased northeasterly flow and non-formation cases with decreased northeasterly flow. If the strength of the northeasterly is increased for the formation case, the stronger cold advection reduces the convective instability around the disturbance center, leading to the weakening of the simulated disturbance. If the strength of the northeasterly is decreased for the non-formation case, the simulated disturbance can develop further into a TC. In summary, strength of the upstream low-level northeasterly flow does affect the environmental conditions around the disturbance center, resulting in the change of TC formation probability over the SCS in the late season.

Tropical Cyclone in the North of the South China Sea as a Factor Affecting the Structure of the Vietnamese Current

2020 ◽  
Vol 56 (4) ◽  
pp. 390-400
Author(s):  
G. A. Vlasova ◽  
Nguyen Ba Xuan ◽  
M. N. Demenok ◽  
Bui Hong Long ◽  
Le Dinh Mau ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
The North

scholarly journals Tropical Cyclone Formations in the South China Sea Associated with the Mei-Yu Front

2006 ◽  
Vol 134 (10) ◽  
pp. 2670-2687 ◽  
Author(s):  
Cheng-Shang Lee ◽  
Yung-Lan Lin ◽  
Kevin K. W. Cheung
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Lower Latitude ◽  
The South ◽  
Low Level ◽  
China Sea ◽  
Tropical Depression ◽  
Stationary Front

Abstract This study examines the 119 tropical cyclone (TC) formations in the South China Sea (SCS) during 1972–2002, and in particular the 20 in May and June. Eleven of these storms are associated with the weak baroclinic environment of a mei-yu front, while the remaining nine are nonfrontal. Seven of the 11 initial disturbances originated over land and have a highly similar evolution. Comparison of the frontal and nonfrontal formation shows that a nonfrontal formation usually occurs at a lower latitude, is more barotropic, develops faster, and possibly intensifies into a stronger TC. Six nonformation cases in the SCS are also identified that have similar low-level disturbances near the western end of a mei-yu front but did not develop further. In the nonformation cases, both the northeasterlies north of the front and the monsoonal southwesterlies are intermittent and weaker in magnitude so that the vorticity in the northern SCS does not spin up to tropical depression intensity. Because of the influence of a strong subtropical high, convection is suppressed in the SCS. The nonformation cases also have an average of 2–3 m s−1 larger vertical wind shear than the formation cases. A conceptual model is proposed for the typical frontal-type TC formations in the SCS that consists of three essential steps. First, an incipient low-level disturbance that originates over land moves eastward along the stationary mei-yu front. Second, the low-level circulation center with a relative vorticity maximum moves to the open ocean with the stationary front. Last, with strengthened northeasterlies, cyclonic shear vorticity continues to increase in the SCS, and after detaching from the stationary front, the system becomes a tropical depression.

Diurnal Cycle of Coastal Convection in the South China Sea Region and Modulation by the BSISO

2021 ◽  
pp. 1-53
Author(s):  
Weixin Xu ◽  
Steven A. Rutledge ◽  
Kyle Chudler
Keyword(s):  
South China Sea ◽  
South China ◽  
The Philippines ◽  
The South China Sea ◽  
Boreal Summer ◽  
Total Precipitation ◽  
The South ◽  
Low Level ◽  
China Sea ◽  
Diurnal Cycles

AbstractUsing 17-yr spaceborne precipitation radar measurements, this study investigates how diurnal cycles of rainfall and convective characteristics over the South China Sea region are modulated by the Boreal Summer Intraseasonal Oscillation (BSISO). Generally, diurnal cycles change significantly between suppressed and active BSISO periods. Over the Philippines and Indochina, where the low-level monsoon flows impinge on coast lines, diurnal cycles of rainfall and many convective properties are enhanced during suppressed periods. During active periods, diurnal variation of convection is still significant over land but diminishes over water. Also, afternoon peaks of rainfall and MCS populations over land are obviously extended in active periods, mainly through the enhancement of stratiform precipitation. Over Borneo, where the prevailing low-level winds are parallel to coasts, diurnal cycles (both onshore and offshore) are actually stronger during active periods. Radar profiles also demonstrate a pronounced nocturnal offshore propagation of deep convection over western Borneo in active periods. During suppressed periods, coastal afternoon convection over Borneo is reduced, and peak convection occurs over the mountains until the convective suppression is overcome in the late afternoon or evening. A major portion (> 70%) of the total precipitation over Philippines and Indochina during suppressed periods falls from afternoon isolated to medium-sized systems (< 10,000 km2), but more than 70% of the active BSISO rainfall is contributed by nocturnal (after 18 LT) broad precipitation systems (> 10,000 km2). However, offshore total precipitation is dominated by large precipitation systems (> 10,000 km2) regardless of BSISO phases and regions.

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