Seasonal characteristics of precipitation occurrences in the core area of the subtropical high.

Based on the NCEP/NCAR reanalysis daily data and GPCP 1DD precipitation data from 1997 to 2006, seasonal characteristics of precipitation occurring in the core area of the subtropical high was investigated by a frequency analysis method. The results indicate that precipitation phenomena occurs in the core area of the subtropical high in each seasons. In summer there exists from 40% to 80% precipitation frequency in the area against less than 50% frequency in other seasons. Generally, the seasonal mean rain rate inside the core area is about 1-2 mm/d in winter and less than 4 mm/d in summer, which contributes about 30%-90% precipitation amount to the local total precipitation. While in summer such contribution is about 50%-90% basically contrary to less than 40% in other seasons. Statistically, the occurrence frequency of updrafts within the core area of the subtropical high varies from 25% to 75% in summer and less than 25% in other seasons. Furthermore, results also expose that there is about 30% frequency for the core area of the subtropical high existing over the eastern parts of China in summer, which is corresponding to 25% and 15% frequency for precipitation and updrafts, respectively. That is the so called a unique precipitation weather pattern, i.e. precipitation under the controlling of the core of the subtropical high, in summer over the eastern parts of China. Additionally, it is found that more than half of the precipitation occurring in the core area of the subtropical high is accompanied with updrafts at 500 hPa against to the rest accompanying with downdrafts. The former may represent deep precipitation circumstances whereas the latter may hint shallow precipitation situations in the core area of the subtropical high.