Convection initiation at a coastal rainfall hotspot in South China: Synoptic patterns and orographic effects

2021 ◽  
Author(s):  
Lanqiang Bai ◽  
Guixing Chen ◽  
Yipeng Huang ◽  
Zhiyong Meng
Keyword(s):  
South China ◽  
Synoptic Patterns ◽  
Orographic Effects ◽  
Convection Initiation

scholarly journals Image Processing of Radar Mosaics for the Climatology of Convection Initiation in South China

2020 ◽  
Vol 59 (1) ◽  
pp. 65-81 ◽  
Author(s):  
Lanqiang Bai ◽  
Guixing Chen ◽  
Ling Huang
Keyword(s):  
South China ◽  
Numerical Models ◽  
Early Morning ◽  
Moist Convection ◽  
Late Night ◽  
Morning Peak ◽  
Spatial Modes ◽  
Triggering Mechanisms ◽  
Deep Moist Convection ◽  
Convection Initiation

AbstractA dataset of convection initiation (CI) is of great value in studying the triggering mechanisms of deep moist convection and evaluating the performances of numerical models. In recent years, the data quality of the operationally generated radar mosaics over China has been greatly improved, which provides an opportunity to retrieve a CI dataset from that region. In this work, an attempt is made to reveal the potential of applying a simple framework of objective CI detection for the study of CI climatology in China. The framework was tested using radar mosaic maps in South China that were accessible online. The identified CI events were validated in both direct and indirect ways. On the basis of a direct manual check, nearly all of the identified CI cells had an organized motion. The precipitation echoes of the cells had a median duration of approximately 2.5 h. The CI occurrences were further compared with rainfall estimates to ensure physical consistency. The diurnal cycle of CI occurrence exhibits three major modes: a late-night-to-morning peak at the windward coasts and offshore, a noon-to-late-afternoon peak on the coastal land, and an evening-to-early-morning peak over the northwestern highland. These spatial modes agree well with those of rainfall, indirectly suggesting the reliability of the CI statistics. By processing radar mosaic maps, such a framework could be applied for studying CI climatology over China and other regions.

Orographic effects on South China Sea summer climate

2008 ◽  
Vol 100 (1-4) ◽  
pp. 275-289 ◽  
Author(s):  
H. Xu ◽  
S.-P. Xie ◽  
Y. Wang ◽  
W. Zhuang ◽  
D. Wang
Keyword(s):  
South China Sea ◽  
South China ◽  
Orographic Effects ◽  
China Sea ◽  
Summer Climate

scholarly journals Winter Eddy Genesis in the Eastern South China Sea due to Orographic Wind Jets

2008 ◽  
Vol 38 (3) ◽  
pp. 726-732 ◽  
Author(s):  
Guihua Wang ◽  
Dake Chen ◽  
Jilan Su
Keyword(s):  
South China Sea ◽  
South China ◽  
Mesoscale Eddies ◽  
Winter Monsoon ◽  
Wind Forcing ◽  
Local Wind ◽  
Orographic Effects ◽  
China Sea ◽  
The Rich ◽  
Anticyclonic Eddies

Abstract Generation of mesoscale eddies in the eastern South China Sea (SCS) in winters during August 1999 to July 2002 is studied with a reduced-gravity model. It is found that the orographic wind jets associated with the northeast winter monsoon and the gaps in the mountainous island chain along the eastern boundary of the SCS can spin up cyclonic and anticyclonic eddies over the SCS. Results suggest that direct wind forcing could be an important generation mechanism for the rich eddy activity in the SCS, and that to simulate this mechanism the resolution of the wind forcing has to be high enough to resolve the local wind jets induced by orographic effects.

scholarly journals Convection Initiation in Monsoon Coastal Areas (South China)

2020 ◽  
Vol 47 (11) ◽  
Author(s):  
Lanqiang Bai ◽  
Guixing Chen ◽  
Ling Huang
Keyword(s):  
South China ◽  
Coastal Areas ◽  
Convection Initiation

The Crucial Role of Synoptic Pattern in Determining the Spatial Distribution and Diurnal Cycle of Heavy Rainfall over the South China Coast

2020 ◽  
pp. 1-47
Author(s):  
Chenli Wang ◽  
Kun Zhao ◽  
Anning Huang ◽  
Xingchao Chen ◽  
Xiaona Rao
Keyword(s):  
South China ◽  
Heavy Rainfall ◽  
Warm Season ◽  
Early Morning ◽  
The South ◽  
Synoptic Patterns ◽  
Low Level ◽  
South China Coast ◽  
China Coast

AbstractSouth China coast suffers frequent heavy rainfall every warm-season. Based on the objective classification method of principle components analysis, the key role of synoptic pattern in determining the heavy rainfall processes occurred over the South China coast in warm season during 2008-2018 is examined in this study. We found heavy rainfall occurs most frequently under three typical synoptic patterns (P1-P3 hereafter) characterized by strong low-level onshore winds. P1 and P3 are featured by a prevailing southwesterly monsoonal flow in the lower troposphere, with heavy rainfall frequently occurring over the inland windward region in the afternoon associated with the orographic lifting and solar heating. The onshore wind of P3 is stronger than P1 as the western Pacific subtropical high extends more westward to 122°E, which induces stronger low-level convergence along the coastline than P1 when the ageostrophic wind veers from offshore to onshore direction in the early morning. Hence, a secondary early morning rainfall peak can be found along the coastline. P2 is characterized by a low-level vortex located over the southwest of south China. Heavy rainfall under P2 usually initiate over the western part of the coastal region in the morning and then propagate towards inland in the afternoon. Overall, the synoptic patterns strongly determine the spatial distribution and diurnal cycle of heavy rainfall over the South China coast. It is closely related to the diurnally varying low-level onshore winds rather than the low-level jets, as well as the different interactions between the low-level onshore winds and the local orography, coastline and land-sea breeze circulations under different synoptic patterns.

scholarly journals Convection Initiation and Growth at the Coast of South China. Part I: Effect of the Marine Boundary Layer Jet

2020 ◽  
Vol 148 (9) ◽  
pp. 3847-3869 ◽  
Author(s):  
Yu Du ◽  
Guixing Chen ◽  
Bin Han ◽  
Chuying Mai ◽  
Lanqiang Bai ◽  
...  
Keyword(s):  
Boundary Layer ◽  
South China ◽  
Marine Boundary Layer ◽  
Rapid Development ◽  
Northern South China Sea ◽  
Heavy Rainfall Event ◽  
Inertial Oscillation ◽  
Low Level ◽  
Convergence Zones ◽  
Convection Initiation

Abstract Convection initiation (CI) and the subsequent upscale convective growth (UCG) at the coast of South China in a warm-sector heavy rainfall event are shown to be closely linked to a varying marine boundary layer jet (MBLJ) over the northern South China Sea (NSCS). To elucidate the dynamic and thermodynamic roles of the MBLJ in CI and UCG, we conducted and analyzed convection-permitting numerical simulations and observations. Compared to radar observations, the simulations captured CI locations and the following southwest–northeast-oriented convection development. The nocturnal MBLJ peaks at 950 hPa and significantly intensifies with turning from southwesterly to nearly southerly by inertial oscillation. The strengthened MBLJ promotes mesoscale ascent on its northwestern edge and terminus where enhanced convergence zones occur. Located directly downstream of the MBLJ, the coastal CI and UCG are dynamically supported by mesoscale ascent. From a thermodynamic perspective, a warm moist tongue over the NSCS is strengthened by the MBLJ-driven mesoscale ascent as well as by a high sea surface temperature. The warm moist tongue farther extends northeastward by horizontal transport and arrives at the coast where CI and UCG occur. Near the CI location, rapid development of a low-level saturated layer is mainly attributed to the mesoscale ascent and low-level moistening associated with the MBLJ. In addition, subsequent CI happens on either side of the original CI along the coast due to the delay of low-level moistening, which partly contributes to linear convective growth. Furthermore, ensemble simulations confirmed that a stronger MBLJ is more favorable to CI and UCG near the coast.

Orographic effects on South China Sea summer climate

2007 ◽  
Author(s):  
Haiming Xu ◽  
Shang-Ping Xie ◽  
Yuqing Wang ◽  
Wei Zhuang ◽  
Dongxiao Wang
Keyword(s):  
South China Sea ◽  
South China ◽  
Orographic Effects ◽  
China Sea ◽  
Summer Climate

scholarly journals Convection Initiation and Growth at the Coast of South China. Part II: Effects of the Terrain, Coastline, and Cold Pools

2020 ◽  
Vol 148 (9) ◽  
pp. 3871-3892 ◽  
Author(s):  
Yu Du ◽  
Guixing Chen ◽  
Bin Han ◽  
Lanqiang Bai ◽  
Minghua Li
Keyword(s):  
Boundary Layer ◽  
South China ◽  
Heavy Rainfall ◽  
Marine Boundary Layer ◽  
Small Scale ◽  
Low Level ◽  
Cold Pools ◽  
Convection Initiation ◽  
Local Moisture

Abstract Through conducting dynamic and thermodynamic diagnoses as well as a series of numerical sensitivity simulations, we investigated the effects of the terrain, coastline, and cold pools on convection initiation (CI) and its subsequent upscale convective growth (UCG) during a case of heavy rainfall along the coast of South China. CI occurred at the vertex of the coastal concave mountain geometry as a combined result of coastal convergence, orographic lifting, and mesoscale ascent driven by the terminus of a marine boundary layer jet (MBLJ). In numerical simulations with the coastline or terrain of South China removed, the coastal CI does not occur or becomes weaker as the MBLJ extends farther north, suggesting that the coastline and terrain play a role in CI. In addition, local small-scale terrain can modulate the detailed location and timing of CI and UCG. When the coastal concave terrain and coastline near the CI are artificially removed or filled by additional mountains, the orographic lifting and the local convergence along the coast correspondingly change, which strongly affects the CI and UCG. From a thermodynamic perspective, the coastal concave terrain plays the role of a local moisture “catcher,” which promotes low-level moistening by blocking water vapor coming from an upstream moist tongue over the ocean. Furthermore, new convection is continuously generated by the lifting of low-level moist southerlies at the leading edges of cold pools that tend to move southeastward because of the blocking coastal mountains. Sensitivity experiments suggest that the MCS becomes weaker and moves more slowly when cold pools are weakened through a reduction of rain-evaporation cooling.

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