Modification of the Boundary Layer over the South China Sea during a Winter MONEX Cold Surge Event

1986 ◽  
Vol 114 (11) ◽  
pp. 2004-2015 ◽  
Author(s):  
Richard H. Johnson ◽  
Jeffery R. Zimmerman
Keyword(s):  
Boundary Layer ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
Cold Surge ◽  
China Sea

Synoptic Disturbances over the Equatorial South China Sea and Western Maritime Continent during Boreal Winter

2005 ◽  
Vol 133 (3) ◽  
pp. 489-503 ◽  
Author(s):  
C-P. Chang ◽  
P. A. Harr ◽  
H-J. Chen
Keyword(s):  
South China Sea ◽  
South China ◽  
Deep Convection ◽  
The South China Sea ◽  
Boreal Winter ◽  
Synoptic Scale ◽  
The South ◽  
Maritime Continent ◽  
Cold Surge ◽  
China Sea

Abstract During boreal winter, the Maritime Continent is a region of deep cumulus convection and heavy precipitation systems that play a major role in several global- and regional-scale processes. Over the western part of this region, the synoptic-scale Borneo vortex, the northeast cold surge, and the intraseasonal Madden–Julian oscillation (MJO) contribute to the variability in deep convection. This work studies the impact on deep convection due to interactions among these three different motion systems. Furthermore, the role of the unique topography of the region is examined with respect to the variability in the synoptic-scale cold surge and Borneo vortex. On the synoptic scale, the interaction of northeast winds with local topography and the dynamic response to the change in latitude contribute to the turning of the winds and localized patterns of deep convection. In days without a Borneo vortex, deep convection tends to be suppressed over the South China Sea and Borneo and enhanced downstream over the landmasses on the western and southern peripheries of the equatorial South China Sea. The pattern is reversed in days with a vortex. The presence of a cold surge enhances this contrast. The surge also interacts with the Borneo vortex, in that the vortex is strengthened and the vortex center shifts from over the South China Sea to be located over the western coast of Borneo. The frequency of cold surges and vortex days is reduced during periods when the MJO is present. Composites of large-scale circulation and outgoing longwave radiation are used to show that often the MJO-related circulation patterns oppose the synoptic-scale cold-surge and vortex circulations. Thus, a primary impact of the MJO is to inhibit weak cold-surge events, which then produces a secondary impact on the Borneo vortex via interactions between the cold-surge winds and the vortex.

scholarly journals Development and Formation Mechanism of the Southeast Asian Winter Heavy Rainfall Events around the South China Sea. Part I: Formation and Propagation of Cold Surge Vortex*

2015 ◽  
Vol 28 (4) ◽  
pp. 1417-1443 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Jenq-Dar Tsay ◽  
Jun Matsumoto ◽  
Jordan Alpert
Keyword(s):  
South China Sea ◽  
South China ◽  
Heavy Rainfall ◽  
The Philippines ◽  
The South China Sea ◽  
The South ◽  
Cold Surge ◽  
China Sea ◽  
Flow Type ◽  
Development Processes

Abstract Examination of the development of cold season heavy rainfall/flood (HRF) events around the South China Sea (SCS) from their parent cold surge vortices (CSVs) shows three new development processes. First, the formation mechanism of the parent CSV of an HRF event [CSV(HRF)] has a preference as to geographic location, flow type of the cold surge inside the SCS, and time of day. The surface trough east of the Philippines, Taiwan, and southern Japan island chain in late fall and the near-equator trough across Borneo in winter facilitate the CSV(HRF) formation in two regions—the vicinity of the Philippines and Borneo. The formation of the Philippine (Borneo) CSV(HRF) occurs at 0600 UTC (0000 UTC) with involvement from the Philippine Sea (PHS)-type (SCS type) of cold surge flow. Second, the flow type of the cold surge determines the CSV(HRF) propagation across the South China Sea. The PHS-type (SCS type) facilitates (hinders) the CSV(HRF) westward propagation. This occurs because the easterly (northerly) flow is greater than (less than) the northerly (easterly) flow at the maximum isotach location of the cold surge flow associated with CSV(HRF) and is centered east of the demarcation line for propagation. This flow-type contrast is substantiated by the vorticity budget analysis for CSV(HRF). The positive 925-hPa vorticity tendency is located west of (coincident with) the 925-hPa vorticity center for the PHS-type (SCS type) of cold surge. Third, the CSV(HRF) development into a HRF event is achieved through multiple interactions of former vortices with sequential cold surges across the South China Sea. The first two CSV(HRF) development processes are reported herein; the last process is presented in Part II.

scholarly journals Two Distinct Types of Extratropical Circulation Anomalies Associated with Cold Surges over the South China Sea

2019 ◽  
Vol 32 (16) ◽  
pp. 5069-5084 ◽  
Author(s):  
Bo Pang ◽  
Riyu Lu
Keyword(s):  
South China Sea ◽  
Rossby Wave ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
Cold Surge ◽  
Siberian High ◽  
China Sea ◽  
Wave Trains ◽  
Cold Surges

Abstract This study investigated the extratropical circulation anomalies responsible for cold surges over the South China Sea in winter. The surge events were identified by the intensity of northerly winds over 110°–117.5°E along 15°N at 925 hPa. Two distinct patterns of sea level pressure (SLP) anomalies in East Asia were found to have a crucial role in inducing cold surges over the South China Sea. Accordingly, the cold surge events were classified into two types. The first type of cold surge is characterized by a pair of SLP anomalies with positive and negative ones centered over China and Japan, respectively, whereas the second type of cold surge is characterized by widespread and persistent positive SLP anomalies over East Asia. Furthermore, the first type of cold surge is accompanied by a deepened East Asian trough and precursory Rossby wave trains across the Eurasian continent in the mid- and upper troposphere, but the latter is not. Prior to both types of the cold surges, the Siberian high is significantly intensified. However, diagnosis of the SLP tendency indicates that the intensification is related to different physical processes. In the first type of cold surge, the Rossby wave trains favor negative vorticity advection and cold advection, inducing intensification of the Siberian high. By contrast, in the second type of cold surge, vorticity advection can be ignored due to the lack of Rossby wave trains, and only the lower-tropospheric cold advection induced by anomalous northerly winds, resulting from the anomalous Siberian high, contributes to the further intensification of the Siberian high.

scholarly journals Development and Formation Mechanism of the Southeast Asian Winter Heavy Rainfall Events around the South China Sea. Part II: Multiple Interactions*

2015 ◽  
Vol 28 (4) ◽  
pp. 1444-1464 ◽  
Author(s):  
Tsing-Chang Chen ◽  
Jenq-Dar Tsay ◽  
Jun Matsumoto
Keyword(s):  
South China Sea ◽  
South China ◽  
Heavy Rainfall ◽  
Cold Season ◽  
The South China Sea ◽  
Northwestern Pacific ◽  
The South ◽  
Cold Surge ◽  
China Sea ◽  
Multiple Interactions

Abstract About 44% of the cold-season heavy rainfall/flood (HRF) events around the South China Sea require six days or longer to develop from the formation time of their parent cold surge vortices (CSVs). Formations for both the parent CSV and HRF event are involved with interactions of the concerned vortices with two different cold surge flows. The occurrence frequency of the East Asian cold surge flow varies from 4.5 to 6 days. The longevous CSVs enable their developments to interact with the second cold surge flows between formations of these CSVs and HRF events. Two requirements for the formation of HRF events are 1) synchronized occurrence of the HRF event and the northwestern Pacific explosive cyclone and 2) simultaneous occurrence of the maximum speeds among westerlies of the northwestern Pacific explosive cyclone and easterlies of the tropical trade winds and the HRF event. These requirements cannot be met by the CSV at its second maximum peak intensity, but the CSV at this stage plays an indispensible role for the formation of the HRF event to make its intensity and rainfall amount larger than those HRF events without this relay intensification. The development of an HRF event through multiple interactions of CSVs with sequential cold surge flows may pose difficulties to numerically simulate/predict the occurrence of these HRF events over the cold-season rainfall centers around the South China Sea.

scholarly journals The South China Sea Monsoon Experiment—Boundary Layer Height (SCSMEX-BLH): Experimental Design and Preliminary Results

2015 ◽  
Vol 143 (12) ◽  
pp. 5035-5053 ◽  
Author(s):  
Huijun Huang ◽  
Weikang Mao
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
South China Sea ◽  
South China ◽  
The South China Sea ◽  
Active Period ◽  
The South ◽  
Layer Height ◽  
China Sea ◽  
Boundary Layer Height

Abstract Knowing the relationship between local convective precipitation and boundary layer processes is critical for forecasting rainstorms. For the South China Sea area, such a forecast is particularly important during the monsoon season. During such a season, the authors examined the boundary layer features at three sites as part of the South China Sea Monsoon Experiment—Boundary Layer Height (SCSMEX-BLH) experiment. The sites are spread from inland to over sea along a 43.4-km line. Here the authors analyze SCSMEX-BLH data from an intensive observing period that includes a convectively suppressed (inactive) period, a period influenced by a tropical storm, and a convectively active monsoon period. Some preliminary findings include the following: 1) The absorption of shortwave radiation over the sea is the primary driver of the land–sea temperature difference. The difference produces a diurnal variation below 400 m, with a warmer surface layer over the coast at night. 2) In the inactive and storm periods, the sensible heat flux is larger than that in the active period, whereas in the active period, the heat flux (primarily latent heat flux) over sea is significant. Also in the active period, the depth of the mixed layer inland is smaller than that in other periods, but the depth on the coast is always higher than that in other periods. 3) In the active period at night, as a monsoon vapor surge advects horizontally over the warm sea surface, a large latent heat flux driven by strong winds aids the growth of marine cumulus, which eventually develop into inland cumulonimbus bringing inland rainfall.

Influence of Siberian Blocking on Long-Lived Cold Surges over the South China Sea

2020 ◽  
Vol 33 (16) ◽  
pp. 6945-6956
Author(s):  
Bo Pang ◽  
Riyu Lu ◽  
Rongcai Ren
Keyword(s):  
South China Sea ◽  
East Asia ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
Sea Level Pressure ◽  
Cold Surge ◽  
China Sea ◽  
Cold Surges ◽  
Extratropical Circulation

AbstractCold surges occur frequently over the South China Sea (SCS) in winter, and most of them last only a few days. However, some cold surge events can persist longer, for instance, more than 5 days. This study focuses on these long-lived cold surge events and investigates the associated extratropical circulation anomalies. The results indicate that long-lived cold surges, characterized as strong northerlies over the SCS, can be triggered by a successive high anomaly center over East Asia. Accompanying this is an anomalously extensive and quasi-stationary anticyclone over Siberia in the midtroposphere, hinting at a more frequent occurrence of Siberian blocking. Further analyses reveal that the blocking frequency is indeed significantly high over 90°–150°E from day −4 to day +2 relative to the onset of long-lived cold surge events. Furthermore, there exist significant correlations between the leading occurrence of Siberian blocking and the sea level pressure (SLP) anomalies over East Asia, which are directly related to long-lived cold surges. The intensification of the high SLP anomaly over East Asia is found to mainly result from cold advection induced by the anomalous northerly winds along the southeastern edge of the Siberian blocking.

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