Zonal propagation of kinetic energy and convection in the South China Sea and Indian monsoon regions in boreal summer

2004 ◽  
Vol 47 (12) ◽  
pp. 1076 ◽  
Author(s):  
Longxun CHEN
Keyword(s):  
Kinetic Energy ◽  
South China Sea ◽  
South China ◽  
Indian Monsoon ◽  
The South China Sea ◽  
Boreal Summer ◽  
The South ◽  
China Sea ◽  
Zonal Propagation

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 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.

scholarly journals Observations of Shoaling Internal Wave Transformation Over a Gentle Slope in the South China Sea

2021 ◽  
Author(s):  
Steven R. Ramp ◽  
Yiing Jang Yang ◽  
Ching-Sang Chiu ◽  
D. Benjamin Reeder ◽  
Frederick L. Bahr
Keyword(s):  
Kinetic Energy ◽  
South China Sea ◽  
Energy Flux ◽  
South China ◽  
The South China Sea ◽  
Wave Transformation ◽  
Recent Theory ◽  
The South ◽  
China Sea ◽  
The Waves

Abstract. Four oceanographic moorings were deployed across the South China Sea continental slope near 21.85° N, 117.71° E, from May 30 to July 18, 2014 for the purpose of observing high-frequency nonlinear internal waves (NLIWs) as they shoaled across a rough, gently sloping bottom. Individual waves required just two hours to traverse the array and could thus easily be tracked from mooring-to-mooring. In general, the amplitude of the incoming NLIWs was a good match with the fortnightly tidal envelope in the Luzon Strait, lagged by 48.5 hours, and were smaller than the waves observed 50 km to the southwest near the Dongsha Plateau. The now-familiar type a-waves and b-waves were observed, with the b-waves always leading the a-waves by 6–8 hours. Most of the waves were remotely generated, but a few of the b-waves formed locally via convergence and breaking at the leading edge of the upslope internal tide. Waves incident upon the array with amplitude less than 50 m and energy less than 100 MJ m−1 propagated adiabatically upslope with little change of form. Larger waves formed packets via wave dispersion. For the larger waves, the kinetic energy flux decreased sharply upslope between 342 m to 266 m while the potential energy flux increased slightly, causing an increasing ratio of potential-to-kinetic energy as the waves shoaled. The results are in rough agreement with recent theory and numerical simulations of shoaling waves.

scholarly journals Kinetic Energy Budget during the Genesis Period of Tropical Cyclone Durian (2001) in the South China Sea

2016 ◽  
Vol 144 (8) ◽  
pp. 2831-2854 ◽  
Author(s):  
Yaping Wang ◽  
Xiaopeng Cui ◽  
Xiaofan Li ◽  
Wenlong Zhang ◽  
Yongjie Huang
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
South China Sea ◽  
Latent Heat ◽  
Energy Budget ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Stage Stage

Abstract A set of kinetic energy (KE) budget equations associated with four horizontal flow components was derived to study the KE characteristics during the genesis of Tropical Cyclone (TC) Durian (2001) in the South China Sea using numerical simulation data. The genesis process was divided into three stages: the monsoon trough stage (stage 1), the midlevel mesoscale convective vortex (MCV) stage (stage 2), and the establishment stage of the TC vortex (stage 3). Analysis showed that the KE of the symmetric rotational flow (SRF) was the largest and kept increasing, especially in stages 2 and 3, representing the symmetrization process during TC genesis. The KE of the SRF was mainly converted from the KE of the symmetric divergent flow (SDF), largely transformed from the available potential energy (APE). It was found that vortical hot towers (VHTs) emerged abundantly, aggregated, and merged within the MCV region in stages 1 and 2. From the energy budget perspective, massive moist-convection-produced latent heat was concentrated and accumulated within the MCV region, especially in stage 2, and further warmed the atmosphere, benefiting the accumulation of APE and the transformation from APE to KE. As a result, the midlevel circulation (or MCV) grew strong rapidly. In stage 3, the intensity and number of VHTs both decreased. However, affected by increasing lower-level inward radial wind, latent heat released by the organized convection, instead of disorganized VHTs in the first two stages, continuously contributed to the strengthening of the surface TC circulation as well as the warm core.

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.

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.

Seasonal variation of eddy kinetic energy in the South China Sea

2012 ◽  
Vol 31 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Hui Wang ◽  
Dakui Wang ◽  
Guimei Liu ◽  
Huiding Wu ◽  
Ming Li
Keyword(s):  
Seasonal Variation ◽  
Kinetic Energy ◽  
South China Sea ◽  
South China ◽  
Eddy Kinetic Energy ◽  
The South China Sea ◽  
The South ◽  
China Sea
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