Analyses Of The Precipitation Spatial Scale Features Over The Contiguous China

The spatial scale of precipitation refers to the space size of contiguous rainfall regions. As an important feature of rainfall, it is closely connected with the formation mechanism and physical process of precipitation. Studying rainfall spatial scale is important to make a more comprehensive understanding of precipitation characteristics and it also has essential significance to quantitative and precise evaluation of numerical prediction model. The present study defined an objective method to quantitatively identify the spatial scale of precipitation, then using TRMM 3B42 and a high spatiotemporal gauge-satellite merged precipitation products to analyze the spatial distribution, seasonal variation and diurnal variation of rainfall spatial scale, the spatial and temporal features of rainfall with different scale. Moreover, the spatial scale of precipitation under different CAM5 horizontal resolution models is discussed. The main conclusions are summarized as follows:(1) Rainfall spatial scale shows distinct regional features and it has significant seasonal and diurnal variation. The spatial scale of precipitation decreases from the southeast to the northwest: the spatial scale at the ocean is more than 600 km, it is in the range of 440-590 km over the eastern plain and the scale of the Tibetan Plateau is less than 440 km. The spatial scale of precipitation is negatively correlated with the altitude. The region where has vaster precipitation scale over eastern China locates the rain belt, and its seasonal variation corresponded with the movement of monsoon rain belt well. In addition, the spatial scale of precipitation has obvious diurnal variation. It reaches the peak in the morning over eastern China, and the peak occurs at night(afternoon) over southern margin(hinterland) of the plateau.(2) Precipitation characteristics of different scales are significantly different. Mid-β scale(20-200km) precipitation accounts for 70% of precipitation frequency over the Tibetan Plateau, and its contribution to total precipitation amount is about 60%. In eastern China, the frequency of mid-α(500-1500km) is similar to mid-β precipitation, and the same as their contribution to the total precipitation amount. It is notable that in considering the concept of the spatial scale of rainfall, the various characteristics of diurnal variations of precipitation can be identified better. Mid-β rainfall mainly occurs in the afternoon due to local convective precipitation initiated by thermodynamic condition, while mid-α rainfall is systematic precipitation with significant regional differences.(3) Evaluation of CAM5 model suggests that model simulates spatial scale of precipitation has a good correspondence with observation in the eastern region of China,but it fails to simulate the spatial scale characteristic of decrease from southeast to northwest. The model basically reproduced the negative correlation between the spatial scale of precipitation and the terrain. Compared to the observations, the area with larger precipitation spatial scale reflects the rain belt’s movement to a certain extent, but it moves rather late and the moving period is more concentrated,. There are differences in precipitation distribution characteristics at different scales in various horizontal resolution simulation. The results indicate that model with higher resolution would enable the simulation much closer to the observation. With a higher model resolution, the most obvious improvement is that the significant increasing of the frequency of small scale precipitation over the Tibetan Plateau.