Analysis of simulated heavy rain over the Yangtze River valley during 11–30 June 1998 using RIEMS

RIEMS’ ability to simulate extreme monsoon rainfall is examined using the 18-month (April 1997 September 1998) integrated results. Model-simulated heavy precipitation over the Yangtze River valley during 11–30 June 1998 is compared with the observation, and the relationships between this heavy rainfall process and the large-scale circulations, such as the westerly jet, low-level jet, and water vapor transport, are analyzed to further understand the mechanisms for simulating heavy monsoon rainfall. The analysis results show that (1) RIEMS can reproduce the pattern of heavy precipitation over the Yangtze River valley during 11–30 June 1998, but it is shifted northwestwards. (2) The simulated West Pacific Subtropical High (WPSH) that controls the East Asia Monsoon evolution is stronger than the observation and is extended westwards, which possibly leads to the north westward shift of the heavy rain belt. (3) The Westerly jet at 200 hPa and the Low-level jet at 850 hPa, both of which are related to the heavy monsoon rainfall, are reasonably reproduced by RIEMS during 11–30 June 1998, although the intensities of the simulated Westerly/Low-level jets are strong and the location of the Westerly jet leans to the southeast, which may be the causes of RIEMS producing too much heavy rainfall in the north of the Yangtze River valley.