A climatological-dynamical analysis associated with precipitation around the southern part of the Himalayas

摘要

The precipitation variability and circulation characteristics around the Himalayas are examined using the Tropical Rainfall Measuring Mission (TRMM) data, the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME) reanalysis, National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP-NCAR) reanalysis, and some of the Indian radiosonde data sets. The observation by precipitation radar on board the TRMM satellite reveals an afternoon maximum of precipitation during the premonsoon season and midnight–early morning maximum during the summer monsoon season over the southern slopes of the Himalayas. The data also shows that the morning precipitation moves southward in the mature monsoon season. The GAME reanalysis reveals a robust diurnal cycle of the atmospheric system that is coherent with the diurnal cycle of precipitation around the southern slopes of the Himalayas. The significant increase of moisture due to the southeasterly wind in the mature monsoon season seems to produce favorable conditions for the midnight–early morning rain. The down-valley wind at midnight probably triggers moist convection. The radiative cooling at the top of clouds may enhance the convection. The precipitation associated with the moist convection seems to generate a cold pool, which results in a density current. The downslope movement of the density current probably induces the southward movement of the precipitation system in the morning.