The diurnal variation of rainfall over the central Tibetan Plateau, central India, and the southern Himalayan foothills is investigated using data acquired by the Tropical Rainfall Measuring Mission (TRMM) during the summer monsoon season from 1998−2007.

　　　Firstly, the central Tibetan Plateau is studied using TRMM precipitation radar (PR) data and high-spatial-resolution data of about 5 km x 5 km, to identify the effect role of complex topographic features on rainfall. GTOPO30 (Global 30 Arc-Second Elevation Data Set) is also used to study topography variation. Diurnal variation in rain rate is analyzed on a monthly basis to determine the characteristics of precipitation. The results are interpreted as precipitation characteristics in a semi arid region with weak prevailing winds near the surface. Over the central Tibetan Plateau July receives the highest amount of rainfall with strong diurnal variation whereas August receives the second the highest amount of rainfall with the least diurnal variation and distinct persistent rainfall during the morning. Precipitation activity over the hilly regions is generally stronger during the late-afternoon than other times of the day. In contrast, valleys and lakes show dominant late-evening peaks, and a secondary persistent morning rainfall peak is distinctly evident over large lakes. However, the time of peak rain rate is delayed with increasing lake size. The strength of diurnal variation is also observed to be weaker over larger lakes.

　　Secondly, diurnal variation of precipitation over central India and the southern foothills is studied for wet and dry periods to compare with the Tibetan Plateau results. Wet and dry periods are investigated and identified as active and break periods of the monsoon over a central India region (CIR) using the TRMM 3B42 dataset. When rainfall decreases over CIR during break periods, rainfall increases over the Himalayan foothills region (HFR) and vice versa during active periods. The CIR and HFR precipitation characteristics are studied using TRMM PR data that is generated with a resolution of about 10 km x 10 km. TRMM LIS (Lightning Imaging Sensor) data and near surface temperature data from NCEP Reanalysis-2 data are utilized. The precipitation characteristics are studied exclusively for wet and dry periods over CIR. HFR is studied to confirm characteristics during wet and dry periods.

　　　During wet periods over CIR and HFR larger amounts of rainfall with a higher frequency of rainfall and higher conditional rain rate is observed than during dry periods. During dry periods over CIR, strong diurnal variation in precipitation is observed with a peak during 12-18 LT. During wet periods over CIR, two peaks appear; a major peak during 12-18 LT and a minor peak during 3-6 LT.　Occurrence of convective rainfall and lightning flashes per mean rain rate is observed higher during dry periods than wet periods. Near surface temperature is also observed higher during dry periods with strong diurnal variation than in wet periods. In contrast average storm height appears higher during wet periods than in dry periods. Over HFR a stronger diurnal variation of precipitation is observed during wet periods than in dry periods with a morning a 03-06 LT peak.　Occurrence of convective rainfall is more during dry periods than during wet periods. But average storm height is observed higher during wet periods than during dry periods.

　　　Generally, during wet periods diurnal variation in rain is weak and an enhanced morning rain peak is observed, than during dry periods. Dry periods have more convective rainfall due to strong solar radiation. Topography including lakes also strongly influences the diurnal variation.