Analyses Of The Rainfall Durationfeatures Over The Contiguous China

Duration time is an important feature of rainfall events. The spatial and temporaldistribution of rainfall duration time can reflect the influence of regional dynamical andthermodynamic processes to hydrological cycle. Studying rainfall duration is important tounderstand the precipitation processes and improve the rainfall forecast. Using12－hourlystation rain-gauge data (A day is divided into two periods with08:00and20:00for the timecut-off point.), this paper analyzes the spatial distribution and seasonal variation of theaveraged rainfall duration time over China, and investigate the spatial and temporal featuresof rainfall events with different duration times. Moreover, the large-scale circulation featurescorresponding to the long-duration rainfall are also examined using NCEP/NCAR reanalysisdata. The main conclusions are summarized as follows:(1) The rainfall duration time over China shows distinct regional spatio-temporalfeatures. For the annual mean rainfall duration time, the differences are more significant overthe areas south of35°N. Over this area, the mean duration time over eastern and westernparts (such as the southeastern China, the southwestern China and the Tibetan Plateau) islonger than that over the middle part (103o－110oE). For the seasonal variation, the annualpeaks of the rainfall duration over most regions occur in the rainy season. However, over theYangtze and Huai River Valley, the Yellow and Huai River Valley and southeastern China,there are also secondary annual peaks in the fall.(2) Annual accumulated rainfall amount of short-duration rainfall (1time duration) inthe coastal of South China is the largest, while there is also a high center of rainfall amountand frequency in the Sichuan Basin. Rainfall amount and frequency in the warm seasons(May to September) are higher than that in cold seasons (October to April) in different region.Long-duration rainfall (no less than3times duration) contributes largely to thespatio-temporal distribution of rainfall in China, especially the seasonal variation of rainfall.Spatial features and seasonal variations of long-duration rainfall are mainly consistent withthe spatio-temporal features of averaged rainfall duration time, while its seasonal variation can also reflect the intra-seasonal movement of the main rain belt. By analyzing thecharacteristics of short-and long-duration in different regions, it is found that the amount andfrequency of long-duration rainfall are larger than those of short-duration rainfall during rainyseasons in most regions expect Northeastern China and the north part of North China.(3) Composite analyses show that the circulation in the long-duration rainfall day overdifferent regions presents similar anomalous pattern. There is a cold anomaly at upper-leverof troposphere above the north of the rainfall area, which tilts southwards with the decreaseof altitude. However, anomalous vapor channels which transport water vapor to long-durationrainfall regions are different between the west regions and the east regions.