Refined characteristics of precipitation and circulation in large-scale rainbelts derived from CMPAS and ERA5 over the Yangtze-Huaihe river valley

Using CMPAS precipitation product and ERA5 reanalysis dataset, spatial characteristics of rainbelts are quantified based on the method of object-based diagnostic evaluation (MODE). The widescale rainbelts are selected and further sorted into zonal and meridional types based on different orientations. The rainbelts in the Yangtze-Huaihe river valley have been classified according to their spatial distributions. Precipitation characteristics and associated atmospheric structure have been analyzed. Comparing spatiotemporal characteristics of different rainbelts, it is found that the widescale rainbelts tend to have a southwest-northeast orientation, and the diurnal variation of precipitation amount (frequency) shows two peaks, i.e., one is in the early-morning (midnight), and the other is in the late afternoon. Precipitation intensity peaks from night to early morning. The zonal rainbelts are southwest-northeast oriented, advancing from south to north during the warm season. Precipitation is concentrated from mid-June to mid-July, corresponding to the Meiyu period. The zonal rainbelts are featured by high frequency of heavy precipitation and broad area. The diurnal variations of precipitation amount, frequency and intensity of the zonal rainbelts are basically the same as those of widescale rainbelts. The meridional rainbelts occur more frequently during the monsoon break period in August, featured by frequent precipitation over relatively small area. The diurnal variation of precipitation amount (frequency) in the meridional rainbelts peaks in the afternoon, and precipitation intensity in the late-afternoon is greater than that at night. Further comparison of the atmospheric structure associated with the two different types reveals that both rainbelts have notable baroclinic structures with warm anomalies in the mid-to-upper levels and cold anomalies in the lower levels. The anomalous circulation of wind field is characterized by an anticyclone in the upper layer and a cyclone in the lower layer. However, the zonal warm anomaly has a large temperature gradient on the north and south sides; while the the meridional warm anomaly has the gradient on the east and west sides. The zonal type is located in the center of the high-level anticyclone. The high-level divergence is conducive to the generation of upward movement, and the low-level southwesterly wind transports abundant water vapor, which is conducive to the formation of large-scale precipitation. The meridional type is located at the back of the high-level anticyclone. Southeasterly and northeasterly wind anomalies prevail in lower levels, leading to meridional spatial distribution of precipitation. Local convergence results in relatively scattered centers of heavy precipitation.