On the Outbreak of South China Sea Summer Monsoon in 1998 and Activity of Atmospheric Intraseasonal Oscillation
1998年南海夏季风的爆发与大气季节内振荡的活动

The relationship between outbreak of the South China Sea Summer Monsoon in 1998 and the activity of atmospheric intraseasonal oscillation is systemically studied by using NCEP re-analysis and TBB (Temperature of Black Body) data. The results show that outbreak of the South China Sea Summer Monsoon in 1998 is closely related to the developing of 30-60 days low-frequency oscillation in the South China Sea and its nearby. The time-longitude (latitude) cross-sections of the 30-60 days low-frequency zonal wind and kinetic energy in the South China Sea and its nearby obviously reflect that the increasing of atmospheric intraseasonal oscillation is excited by the developing of the 30-60 days low-frequency cyclone over the Philippines area and its expanding westwards. There is no clear as- sociation with the low-frequency cyclone activity over the Bay of Bengal. Meanwhile, near to outbreak of the South China Sea Summer Monsoon, the low-frequency kinetics at 850 hPa over the South China Sea is much stronger than that of its nearby, but it is much weaker at 200 hPa. This reflects the weak to strong vertical structure feature from the lower to upper troposphere. The further analyses show the local activity characteristics of the atmospheric intraseasonal oscillation over the South China Sea and its nearby. However, after the monsoon outbreak, the low-frequency oscillation begins to propagate northwards and become the important pass to influence the weather and climate in East Asia. Additionally, the developing characteristics of the 30-60 days kinetic over the South China Sea in 1980 and 1986 are very similar to that of 1998. It represents that the local activity feature of the atmospheric intra-seasonal oscillation over the South China Sea and its nearby is not only in 1998, and has the common effect on the outbreak of the South China Sea Summer Monsoon.