IMPACTS OF SURFACE SENSIBLE HEAT FLUXES IN THE KEY AREAS OF THE TIBETAN PLATEAU ON INTERANNUAL VARIATION OF THE SCS SUMMER MONSOON INTENSITY

The impacts of the variations of surface heat fluxes over the Tibetan Plateau (TP) and surrounding areas on the interannual variation of the South China Sea (SCS) summer monsoon intensity is analyzed using the NCEP/NCAR reanalysis monthly sensible heat flux data from 1949 to 2000 and monthly mean wind and temperature field data from 1958 to 1997.The results show that there is a distinct interdecadal trend in sensible heat over the key areas of the TP and the SCS summer monsoon intensity as well as South Asia high intensity (SAHI),the transition occurs in late 1970s.The SCS summer monsoon intensity has a significant positive correlation with the variation of surface sensible heat fluxes over the northwestern part of the TP,while it has negative correlation with the surface sensible heat fluxes in the south of the TP.During the strong SCS summer monsoon year,the vertical ascending motion in the northwestern TP is strengthened,but in the southern TP it is weakened,and the position of the South Asian high is northward,while in the weak summer monsoon year,it is in the contrary.The SAHI is closely related to variation of surface heat fluxes over the TP and surrounding areas,and there exists a negative relationship between the SCS summer monsoon intensity and SAHI.

A PRIMARY STUDY OF SUMMER MONSOON INDEX OVER THE SOUTH CHINA SEA AND EAST ASIA BASED ON SATELLITE OBSERVATION

The results by statistical analysis of black body Temperature （TBB） pentad mean from the Japanese GMS in the period of May to August, 1980-2002, show that the summer monsoon index （SMI） is defined to be the pentad mean TBB≤273 K. Its intensity includes three levels： TBB〉268 K for weak monsoon, 268 KETBB〉263 K for normal monsoon and TBB≤263K for strong monsoon over the South China sea and East Asia. In the meantime, a diagnostic method using TBB pentad anomaly is also introduced to help identify monsoon intensity. The SMI is used to run statistical analyses of the initial onset of the monsoon and its pentad variations with the year and month. A fairly close relationship is found between pentad monsoon activity and heavy rainfall periods in the two typical flood years of 1994 and 1998, which resulted from heavy rainfall over the Yangtze River basin and south China.

THE RELATIONSHIP BETWEEN SOUTH CHINA SEA SOUTHWEST MONSOON ANOMALIES AND IMPORTANT WEATHER IN GUANGDONG PROVINCE DURING THE RAINING SEASONS

The activity of South China Sea southwest monsoon (SCSSM) has direct impacts on the anomalies of important weather in Guangdong province during the raining seasons. So it is necessary to explore thoroughly the activity pattern of SCSSM and its relationship with important weather anomalies in the province. In this paper, the methods of composite analysis and correlation statistics are used to study the relationship between the onset date and intensity of SCSSM and the important weather, such as precipitation trends in Guangdong province during the annually first and second raining seasons, the timing of the annually first and last typhoon and the number of typhoons landing in Guangdong province. The results show that the rainfall is less than normal during the first raining season, but more than normal during the second one and there are more tropical cyclones landing in Guangdong province in the years of early SCSSM onset. The rainfall is more than normal during the second raining season and there are more tropical cyclones landing in Guangdong province in the years of strong SCSSM. The relationship between the SST of April - June, July - September and previous winter (December - February) and 500 hPa geopotential height and the onset date and intensity of SCSSM is analyzed. Some mechanisms between the onset dates and intensity of SCSSM and the important weather anomalies in Guangdong province are preliminarily explored. The results can be used for reference in short-term climate forecast.

Characteristics of Thermal and Geopotential Height Differences Between Continent and Ocean and Its Role in the Strength of the Asian Summer Monsoon

The interdecadal factors affecting the summer monsoon winds over Somalia and the South China Sea were studied. Global geopotential heights and wind velocity fields of the 850-hPa and 200-hPa pressure levels, as well as sea surface temperature anomaly data and correlation coefficients were analyzed. The monsoons over Somalia and the South China Sea were found to be two different monsoon systems, operating on different mechanisms and being affected by different oceanatmosphere interactions. The intensity of the Asian subtropical summer monsoon is influenced by the intensity of the summer monsoon over Somalia in the month of June and by the intensity of the summer monsoon over the South China Sea in the months of June and July. The summer monsoon wind strength over Somalia is affected by regional factors, such as the heating of the Tibetan plateau, and by global mechanisms, such as the subtropical heat exchange with Antarctica. The summer monsoon over the South China Sea is affected by different ocean-atmosphere interactions. The Somalia and subtropical summer monsoons have wind blowing down the pressure gradient from area over ocean to that over land, like typical summer monsoons. The South China Sea summer monsoon has winds that blow down the pressure gradient from area over land to that over ocean. The South China Sea summer monsoon is affected by the Kuroshio Current off the east coast of Japan.

A STUDY OF CIRCULATION CHARACTERISTICS AND INDEX OF SOUTH CHINA SEA SUMMER MONSOON

Based on height and wind data of NCEP/NCAR and OLR data,patterns of upper air circulation from April to October have been analyzed,and the South China Sea (SCS) Summer Monsoon Onset (SMO) and retreat have been defined.The empirical formula fitting to the onset index of the SCS SMO has been established,and the onset and ending time of monsoon,together with the intensity index sequence during 1953—1999 are given by the analysis of characteristics of thermodynamic and dynamic factors during the process of SMO.The emergence and development of symmetric vortex pair at both sides of the equator in tropical East Indian Ocean,which may excite the SCS SMO,can be taken as a short-term prediction indicator of SMO.

Relationships between Springtime Sea Surface Temperatures in Different Indian Ocean Domains and Various Asian Monsoons from Late Spring to the Following Summer

We investigate the relative importance of spring sea surface temperatures(SSTs)in different Indian Ocean(IO)domains,especially the northern and southern IO,for the development and intensity of the Asian summer monsoon.By performing unsupervised neural network analysis,the self-organizing map,we extract distinct patterns of springtime IO SST.The results show that the uniform warming(cooling)of the southern IO plays a crucial role in the warming(cooling)of both the basin-wide IO and tropical IO.The southern IO thus well represents the associations of basinwide IO and tropical IO with the Asian summer monsoon,and is instrumental in the relationship between the IO and summer monsoon.A warming in the southern IO is closely related to the weakening of large-scale meridional monsoon circulation in May and summer(June–August),including suppression of the South Asian monsoon development in May and the East Asian monsoon in summer.On the other hand,a warming in the northern IO appears to be associated with an earlier South Asian monsoon onset and a stronger East Asian monsoon.In summer,the connection of the springtime IO SST with the South Asian monsoon weakens,but that with the East Asian monsoon strengthens.Finally,a robust negative correlation is found between the warming of various IO domains and the development and intensity of the Southeast Asian monsoon.