Relationship between the Onset of the South China Sea Summer Monsoon and Abnormal Variations of frontal Precipitation during the First Rainy Period in South China

The daily NCEP/NCAR reanalyzed data and daily rainfall data during 1958-2000 from the National Climate Center of China Meteorology Administrator are used to analyze dynamic and thermodynamic characteristics under the abnormal onset of South China Sea Summer Monsoon.Relationships among the cold air activity in South China,precipitation in the yearly first rainy period and abnormal onset of the South China Sea Summer Monsoon are explored.The results indicate: 1) the abnormal change of onset dates of the South China Sea Summer Monsoon is mostly decided by zonal wind.2) The early(late) onset of the South China Sea Summer Monsoon is related to the early(late) reversal of the troposphere temperature meridional gradient under 200 hPa and the trend transmitting downwards.3) The more active cold air is in spring and the more precipitation there is in South China,the earlier the onset of the South China Sea Summer Monsoon occurs.4) A synthetic physical concept model about the relationships among South China cold air activity,precipitation in the yearly first rainy period and anomalous onset of the South China Sea Summer Monsoon is presented.