Characteristics of Monsoon Rainfall around the Himalayas Revealed by TRMM Precipitation Radar

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Abstract
The climatological features of the diurnal cycle and its spatial and temporal variability are investigated around the Himalayas using hourly, 0.05° × 0.05° grid, near-surface rainfall data from the Precipitation Radar (PR) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite during June–July–August (JJA) of 1998–2002. Though sampling errors inherent to TRMM PR measurements around the Himalayas could influence results, PR-observed precipitation features show agreement with previous studies in this region. The analysis of precipitation characteristics presented here is based on two rain-rate thresholds: (a) light rain rate (≤5 mm h−1), and (b) moderate to heavy rain rate (>5 mm h−1). The results suggest that afternoon to evening precipitation is noticed as embedded convection within a large region of light rain over the south-facing slopes of the Himalayas. The moderate to heavy conditional rain rate exhibits a relatively stronger diurnal cycle of precipitation in this region. However, this may be biased because of sampling. Almost all the Tibetan Plateau shows light rain activity. The Tibetan Plateau and northern Indian subcontinent regions are characterized by daytime maximum precipitation. From the analysis of near-surface rainfall over the finescale topography, it is observed that daytime (1200–1800 LT) precipitation is concentrated over the ridges and strong ridge–valley gradients with rain appearing over the south-facing slopes of the Himalayas. During midnight–early morning, intense rainfall concentrates over the ridges as well as in river valleys. Precipitation broadening and movement are noticed during this time period.