scholarly journals The Moisture Sources and Transport Processes for a Sudden Rainstorm Associated with Double Low-Level Jets in the Northeast Sichuan Basin of China

Atmosphere ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 160 ◽  
Author(s):  
Fangli Zhang ◽  
Guoping Li ◽  
Jun Yue
Keyword(s):  
South China Sea ◽  
South China ◽  
Moisture Transport ◽  
Sichuan Basin ◽  
Arabian Sea ◽  
Low Level ◽  
China Sea ◽  
Northeast Sichuan Basin ◽  
Low Level Jets ◽  
Low Level Jet

A sudden rainstorm that occurred in the northeast Sichuan Basin of China in early May 2017 was associated with a southwest low-level jet (SWLJ) and a mountainous low-level jet (MLLJ). This study investigates the impact of the double low-level jets (LLJs) on rainfall diurnal variation by using the data from ERA5 reanalysis, and explores the characteristics of water vapor transport, including the main paths and sources of moisture, by using the HYSPLIT-driven data of the ERA—interim, GDAS (Global Data Assimilation System), and NCEP/NCAR reanalysis data. The analysis shows that the sudden rainstorm in the mountain terrain was located at the left side of the large-scale SWLJ at 700 hPa, and at the exit region of the meso-scale MLLJ at 850 hPa. The double LLJs provide favorable moisture conditions, and the enhancement (weakening) of the LLJs is ahead of the start (end) of the rainstorm. The capacity of the LLJ at 850 hPa with respect to moisture convergence is superior to that at 700 hPa, especially when the MLLJ and the southerly LLJ at 850 hPa appear at the same time. The HYSPLIT backward trajectory model based on Lagrangian methods has favorable applicability in the event of sudden rainstorms in mountainous terrain, and there is no special path of moisture transport in this precipitation event. The main moisture sources of this process are the East China Sea–South China Sea, the Arabian Sea–Indian Peninsula, the Bay of Bengal, and the Middle East, accounting for 38%, 34%, 17% and 11% of the total moisture transport, respectively. Among them, the moisture transport in the Bay of Bengal and the South China Sea–East China Sea is mainly located in the lower troposphere, which is below 900 hPa, while the moisture transport in the Arabian Sea–Indian Peninsula and the Middle East is mainly in the middle and upper layers of the troposphere. The moisture changes of the transport trajectories are affected by the topography, especially the high mountains around the Sichuan Basin.

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.

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.

Interdecadal Variations of Meridional Winds in the South China Sea and Their Relationship with Summer Climate in China*

2010 ◽  
Vol 23 (4) ◽  
pp. 825-841 ◽  
Author(s):  
Chunhui Li ◽  
Tim Li ◽  
Jianyin Liang ◽  
Dejun Gu ◽  
Ailan Lin ◽  
...  
Keyword(s):  
South China Sea ◽  
East Asia ◽  
South China ◽  
The South China Sea ◽  
Central China ◽  
Convective Heating ◽  
Tropospheric Temperature ◽  
The South ◽  
Low Level ◽  
China Sea

Abstract Analysis of the NCEP and 40-yr ECMWF Re-Analysis (ERA-40) data and the Xisha Island station observation indicates that the low-level meridional wind (LLMW) over the South China Sea (SCS) experienced an interdecadal variation since the late 1970s. The LLMW change is associated with the reduction of tropospheric temperature in midlatitude East Asia. A mechanism is put forward to explain the triggering and maintenance of the tropospheric cooling. The enhanced convective heating over the southern South China Sea results in a meridional vertical overturning circulation, with anomalous descending motion appearing over continental East Asia. The anomalous descending motion reduces the local humidity through both anomalous low-level divergence and dry vertical advection. The decrease of the local tropospheric humidity leads to the enhanced outgoing longwave radiation into space and thus cold temperature anomalies. The decrease of the temperature and thickness leads to anomalous low (high) pressure and convergent (divergent) flows at upper (lower) levels. This further enhances the descending motion and leads to a positive feedback loop. The fall in tropospheric temperature over continental East Asia reduces the land–sea thermal contrast and leads to the weakening of cross-equatorial flows and the LLMW over SCS. A further diagnosis indicates that the LLMW is closely linked to the summer precipitation and temperature variations in China on interdecadal time scales. A weakening of the LLMW after 1976 is associated with a “−, +, −” meridional rainfall pattern, with less rain in Guangdong Province and north China but more rain in the Yangtze and Huaihe River basins and northeast China, and a “+, −, +” temperature pattern, with increased (decreased) surface temperature in the south and north (central) China.

Fall Persistence Barrier of Sea Surface Temperature in the South China Sea Associated with ENSO*

2007 ◽  
Vol 20 (2) ◽  
pp. 158-172 ◽  
Author(s):  
Jau-Ming Chen ◽  
Tim Li ◽  
Ching-Feng Shih
Keyword(s):  
South China Sea ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
South China ◽  
The South China Sea ◽  
Sea Surface ◽  
The South ◽  
Low Level ◽  
China Sea ◽  
Philippine Sea

Abstract The authors investigate persistence characteristics of sea surface temperature (SST) in the South China Sea (SCS) in association with El Niño–Southern Oscillation (ENSO). It is found that a persistence barrier exists around October and November. This fall persistence barrier (FPB) is well recognized in the developing phase of strong ENSO cases, but becomes vague in weak ENSO and normal (non-ENSO) cases. During a strong El Niño developing year, salient features of the SCS SST anomaly (SSTA) associated with the FPB include a sign reversal between summer and winter and a rapid warming during fall. One possible cause of these SST changes, as well as the occurrence of the FPB, is the development and evolution of a low-level anomalous anticyclone (LAAC). The analyses show that the LAAC emerges in the northern Indian Ocean in early northern fall, moves eastward into the SCS during fall, and eventually anchors in the Philippine Sea in northern winter. This provides a new scenario for the generation of the anomalous Philippine Sea anticyclone previously studied. Its eastward movement appears to result from an east–west asymmetry, relative to the anticyclonic circulation center, of divergent flow and associated atmospheric vertical motion/moisture fields. The eastward passage of the LAAC across the SCS warms the underlying SST first via increased absorption of solar heating in October as it suppresses convective activities in situ, and next via decreased evaporative cooling in November and December as the total wind speed is weakened by the outer flows of the eastward-displacing LAAC. As such, the SCS SST changes quickly from a cold to a warm anomaly during fall, resulting in an abrupt change in anomaly patterns and the occurrence of the FPB. Analyses also suggest that the LAAC development during fall is relatively independent from the preceding Indian summer monsoon and the longitudinal propagation features of the ENSO-related Pacific SSTA. The aforementioned ocean–atmosphere anomalies contain an opposite polarity in a strong La Niña event. The low-level circulation anomaly weakens in intensity during weak ENSO cases and simply disappears during normal cases. As a result, the SCS FPB becomes indiscernible in these cases.

scholarly journals Air–Sea Relationship Associated with Precipitation Anomaly Changes and Mean Precipitation Anomaly over the South China Sea and the Arabian Sea during the Spring to Summer Transition

2015 ◽  
Vol 28 (18) ◽  
pp. 7161-7181 ◽  
Author(s):  
Renguang Wu ◽  
Wenting Hu
Keyword(s):  
South China Sea ◽  
South China ◽  
Arabian Sea ◽  
Precipitation Anomaly ◽  
Surface Heat ◽  
Heat Fluxes ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Precipitation Anomalies

Abstract The period from April to June is the time of transition from spring to summer over the north Indian Ocean and the South China Sea. Analysis shows that precipitation anomaly changes from April to June may indicate summer (June–August) mean precipitation anomalies over the South China Sea and the Arabian Sea. This study documents and compares the evolution of precipitation, surface wind, and sea surface temperature (SST) anomalies during the spring to summer transition corresponding to April–June precipitation anomaly changes and April–June mean precipitation anomalies over the South China Sea and the Arabian Sea. Over the South China Sea, a clear signal of local air–sea interaction is identified corresponding to the precipitation anomaly change, as indicated by a sequence of less precipitation, higher SST, more precipitation, and lower SST. In contrast, the mean precipitation anomaly features a response to remote SST forcing and a local forcing of atmosphere on the ocean. The evolution of surface heat flux anomalies supports the air–sea interaction over the South China Sea during the transition season. Over the Arabian Sea, local SST forcing contributes to both precipitation anomaly changes and mean precipitation anomalies through modulating atmospheric stability. A local negative feedback of atmosphere on SST is observed in the Arabian Sea as in the South China Sea. The surface heat fluxes make a large contribution to local SST change before May in the South China Sea but a small one in the Arabian Sea. Surface heat fluxes are important for local SST change after May in both the South China Sea and the Arabian Sea.

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