夏季风期间南海对流活动对西北太平洋热带气旋的影响分析

利用1979-2008年NCEP／NCAR逐日再分析资料、NOAA的OLR逐日资料和西北太平洋热带气旋（TC）资料，分析了夏季风期间南海（105～120°E，5-20°N）对流活动的季节内振荡（ISO）特征及其对西北太平洋TC的生成及路径的影响，并采用TC路径模式从大尺度环境场角度初步探讨了ISO对TC运动的影响机制，结果表明，（1）夏季风期间的南海对流活动存在活跃期、不活跃期交替更迭的ISO现象，与之对应的季风环流型存在显著差异：南海对流活跃（不活跃）表示南海夏季风活跃（不活跃），南海．西北太平洋季风槽强（弱）且向东伸展（向西撤退），副热带高压偏东（西），季风环流强（弱）。（2）南海夏季风活跃（不活跃）期，TC生成频数多（少）且生成位置偏西（东）。（3）针对西行进入135°E以西，25°N以南的这类西北太平洋TC（WNP-TC），在活跃期，多以偏西或西北路径直行进入南海；而不活跃期时，多转向北上不进入南海。（4）路径模式模拟结果显示：南海季风活跃（不活跃）时，大尺度环境场的引导作用有利于WNP-TC直行进入南海（转向北上，不进入南海）。同时，WNP-TC的生成位置越偏西越有利于WNP-TC进入南海。

南海夏季风对流季节内振荡的频谱变化特征

利用1980～1997年TBB资料和海表温度(SST)资料,诊断分析了南海对流季节内变化频谱及强度的变化特征,并探讨对流季节内振荡强度与对流本身强度以及南海SST之间的关系。结果表明,南海对流季节内变化强度及频谱存在明显的年内变化、年际变化和年代际变化特征;南海地区夏半年对流及其ISO1强度与后期冬季南海SST有一定的关系,当夏半年对流较强(弱),ISO1较强(弱)时,则后期冬季南海SST偏低(高)。

CHARACTERISTICS OF FREQUENCY SPECTRUM VARIATION OF INTRASEASONAL OSCILLATION OF CONVECTION DURING SOUTH CHINA SEA SUMMER MONSOON

Datasets of equivalent temperature of black body (TBB) and sea surface temperature (SST)ranging from 1980 to 1997 are used to diagnose and analyze the characteristics of frequency spectrum andstrength of intraseasonal variation of convection. The relationship between the strength of intraseasonaloscillation of convection, strength of convection itself and SST in the South China Sea (SCS) is studied. It isshown that, there are distinguishable annual, interannual and interdecadal variations in both strength andfrequency spectrum of intraseasonal variation of convection in SCS. There are connections between strength ofconvection, strength of ISO1 in the summer half (s.h.) year and SST in ensuing winter half (w.h.) year in SCS.The strong (weak) convection and strong (weak) ISO1 are associated with negative (positive) bias of SST inensuing w.h. year in SCS.

DETERMINATION OF ONSET DATE OF THE SOUTH CHINA SEA SUMMER MONSOON IN 2006 USING LARGE-SCALE CIRCULATIONS

Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection intensities are widely used to determine the SCSSM onset.The methods can be used successfully in most of the years but not in 2006.Due to the intrusion of Typhoon Chanchu(0601)that year,the usual method of determining SCSSM onset date by utilizing the SCS regional indices is less capable of pinpointing the real onset date.In order to solve the problem,larger-scale situations have to be taken into account.Zonal and meridional circulations would be better to determine the break-out date of SCSSM in 2006.The result indicates that its onset date is May 16.Moreover,similar onset dates for other years can be obtained using various methods,implying that large-scale zonal and meridional circulations can be used as an alternative method for determining the SCSSM onset date.

Influence of the Convection over the South China Sea on the Summer Precipitation of Shandong Province

The pentad average minimum outgoing longwave radiation (OLR) data over the northern South China Sea (SCS) are selected as indexes to analyze the intensity of the convection connected with the SCS monsoon onset. Statistic analysis demonstrates that the index can account for the intensity of the SCS monsoon about, at least, 75%. A significant negative correlation (confident level over 90%) between Shandong’s summer rainfall and the index is found only in the period of 24-26 pentads and limited to the area above the deeper water basin of the SCS (10°-20°N, 110°-117.5°E). Thus the minimum OLR over the deeper water basin during 24-26 pentads can be used as a valuable predictor for the long lead forecast of the precipitation. The 500 hPa geopotential height data in the Northern Hemisphere for the period from 1951 to 2000 are used in order to characterize the physical mechanisms involved. The composite anomalies of the 500 hPa level allow for the identification and detection of the teleconnection of the East Asia North America (EAP) pattern that is responsible to some extent for the interannual variability of the precipitation of Shandong Province. Besides, the interannual differences of the intraseasonal variations (ISV) of OLR and their northward transmission probably make a contribution to the position of the subtropical high which is vital for the summer rainfall in the province.

THE CLIMATIC CHARACTERISTICS OF SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA I.40-YEAR AVERAGE

By using 40-year NCEP reanalysis daily data (1958-1997), we have analyzed the climatic characteristics of summer monsoon onset in the South China Sea (105E ~ 120E, 5N ~ 20N, to be simplified as SCS in the text followed) pentad by pentad (5 days). According to our new definition, in the monsoon area of the SCS two of the following conditions should be satisfied: 1) At 850hPa, the southwest winds should be greater than 2m/s. 2) At 850 hPa, seq should be greater than 335K. The new definition means that the summer monsoon is the southwest winds with high temperature and high moisture. The onset of the SCS summer monsoon is defined to start when one half of the SCS area (105E ~ 120E,5N ~ 20N) is controlled by the summer monsoon. The analyzed results revealed the following: 1) The summer monsoon in the SCS starts to build up abruptly in the 4th pentad in May. 2) The summer monsoon onset in the SCS is resulted from the development and intensification of southwesterly monsoon in the Bay of Bengal. 3) The onset of the summer monsoon and establishment of the summer monsoon rainfall season in the SCS occur simultaneously. 4) During the summer monsoon onset in the SCS, troughs deepen and widen quickly in the lower troposphere of the India; the subtropical high in the Western Pacific moves eastward off the SCS in the middle troposphere; the easterly advances northward over the SCS in the upper troposphere.

Modeling underwater transport of oil spilled from deepwater area in the South China Sea

Based on a Lagrangian integral technique and Lagrangian particle-tracking technique,a numerical model was developed to simulate the underwater transport of oil from a deepwater spill. This model comprises two submodels: a plume dynamics model and an advection-diffusion model. The former is used to simulate the stages dominated by the initial jet momentum and plume buoyancy of the spilled oil,while the latter is used to simulate the stage dominated by the ambient current and turbulence. The model validity was verified through comparisons of the model predictions with experimental data from several laboratory flume experiments and a field experiment. To demonstrate the capability of the model further,it was applied to the simulation of a hypothetical oil spill occurring at the seabed of a deepwater oil/gas field in the South China Sea. The results of the simulation would be useful for contingency planning with regard to the emergency response to an underwater oil spill.