scholarly journals The Effect of Boreal Summer Intraseasonal Oscillation on Evaporation Duct and Electromagnetic Propagation over the South China Sea

Atmosphere ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1298
Author(s):  
Wentao Jia ◽  
Weimin Zhang ◽  
Jiahua Zhu ◽  
Jilin Sun
Keyword(s):  
South China Sea ◽  
South China ◽  
Dominant Role ◽  
Intraseasonal Oscillation ◽  
The South China Sea ◽  
Boreal Summer ◽  
The South ◽  
Boreal Summer Intraseasonal Oscillation ◽  
China Sea ◽  
Evaporation Duct

Intraseasonal oscillation of the evaporation duct, lasting 30–60 days, has been identified over the South China Sea (SCS) summer monsoon region based on multiple reanalyses and observational data. The boreal summer intraseasonal oscillation (BSISO) causes anomalies at the air–sea boundary and thus plays a dominant role in modulating the variation of the evaporation duct. The height and strength of the duct enhance/suppress during the negative/positive phase of the BSISO over the SCS. This results from the fact that active BSISO convection reduces solar radiation reaching the sea surface by increasing cumulus cloud cover, whereupon precipitation and water vapor transported by the enhanced southwest jet increase humidity over the air–sea boundary. Reduced air–sea temperatures and humidity differences lead to a weaker evaporation duct. Usually, the temporal evolution of the evaporation duct lags 2–4 days behind the BSISO, with the center of evaporation duct anomalies farther south than the BSISO. Simulated electromagnetic fields substantively influence the condition of the evaporation duct, with obvious over-the-horizon and radar blind spot effects in the typical negative phase of the BSISO, which is very different from standard atmospheric conditions.

scholarly journals Mechanisms of Northward-Propagating Intraseasonal Oscillation over the South China Sea during the Pre-Monsoon Period

2019 ◽  
Vol 32 (11) ◽  
pp. 3297-3311 ◽  
Author(s):  
Bin Zheng ◽  
Yanyan Huang
Keyword(s):  
South China Sea ◽  
South China ◽  
Intraseasonal Oscillation ◽  
The South China Sea ◽  
Boreal Summer ◽  
The South ◽  
China Sea ◽  
Northward Propagation ◽  
The Mean ◽  
Barotropic Vorticity

Abstract In the present study, the spatiotemporal structures of the northward-propagating intraseasonal oscillation (ISO) over the South China Sea (SCS) in the premonsoon period are analyzed by using the TropFlux air–sea flux and the JRA-55 reanalysis datasets. It is found that the SCS ISO is significant in the premonsoon season with a strong component of the northward propagation and that the mean state is different from that of summertime. Moreover, there are similar structures to those of a boreal summer ISO event except for the perturbation vorticity with no obvious phase leading. An internal atmospheric dynamics mechanism is proposed to understand the cause of the northward propagation of the ISO during the premonsoon period based on the spatial and temporal structures of the ISOs. The key process associated with this mechanism is the barotropic vorticity advection by the mean barotropic southerly winds, and the main barotropic vorticity around the convection center can be induced by the vertical advection of the mean vorticity. Low-level moisture convergence caused by anomalous flow is a supplementary mechanism to drive the ISOs northward during the premonsoon period, particularly over the northern SCS. In this mechanism, the SST-induced wind anomalies play a more important role than the convection-induced wind anomalies. The summer monsoon circulation has not built up during the premonsoon period, and thus the vertical wind shear effect and the barotropic vorticity effect associated with the meridional advection of baroclinic vorticity are not essential to cause the northward propagation of the ISOs over the SCS.

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 Fading Characteristics in Evaporation Duct: Fade Margin for a Wireless Link in the South China Sea

IEEE Access ◽  
2018 ◽  
Vol 6 ◽  
pp. 11038-11045 ◽  
Author(s):  
Khurram Shabih Zaidi ◽  
Varun Jeoti ◽  
Micheal Drieberg ◽  
Azlan Awang ◽  
Asif Iqbal
Keyword(s):  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Wireless Link ◽  
The South ◽  
China Sea ◽  
Evaporation Duct

scholarly journals Decadal Change in Tropical Cyclone Activity over the South China Sea around 2002/03

2015 ◽  
Vol 28 (15) ◽  
pp. 5935-5951 ◽  
Author(s):  
Yao Ha ◽  
Zhong Zhong
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Boreal Summer ◽  
Decadal Change ◽  
The South ◽  
China Sea ◽  
Zonal Circulation ◽  
Decadal Scale

Abstract This study investigates the decadal change in tropical cyclone (TC) activity over the South China Sea (SCS) in the boreal summer (June–August) since the early 1990s and explores possible causes behind it. Results show that the SCS TC activity experienced an abrupt decadal decrease at around 2003/03. Compared to the TC activities from the early 1990s to 2002, the number of TCs formed in the SCS markedly decreased from 2003 through the early 2010s. Moreover, most of the TCs were primarily confined within the SCS basin during this period. The TCs that formed during the period of 2003–11 usually moved west-northwestward and rapidly weakened after making landfall. It is found that a significant decadal-scale sea surface temperature (SST) warming occurred in the northern Indian Ocean and the western Pacific Ocean after 2002 while convection intensified over the tropical regions between 60° and 80°E and around 150°E, respectively. The warm SST anomalies induced an anomalous subsiding flow over the SCS basin via the Walker-like (zonal) circulation. Meanwhile, anomalously dry, sinking air around 5°–20°N derived from local Hadley (meridional) circulation reinforced the subsiding flow of the zonal circulation. The above circulation patterns suppressed TC genesis over the northern SCS, leading to the decadal decrease in TC activity that occurred around 2002/03. In addition, in conjunction with the local anomalous easterly flow, the intraseasonal atmospheric variability over the SCS has decreased since the early 2000s. This is unfavorable for the development of synoptic-scale disturbances and may also contribute to the decadal decrease in TC activity.

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