Abstract
Distribution of rainfall at high spatial resolutions is needed to understand the orography-rainfall relationship over complex terrains. In this work, we present rainfall distribution at 1 km × 1 km spatial resolution and its diurnal variation during a summer monsoon season using the data collected with an X-band radar installed at Mandhardev, a site in the Western Ghats (WG) of India. Rainfall characteristics [rainfall amount (RA), rainfall frequency (RF) and rainfall rate (RR)] are reported. Our analysis reveals the exact position of rainfall maxima across the WG. A rainfall maximum zone (RMZ) with RA values exceeding 7000 mm has been identified. High RA over RMZ is strongly modulated by diurnal heating and primarily due to high RF, but RR also matters. Attempt is made to understand the interaction between the dynamics and underlying orographic features in deciding the location of rainfall maximum. The position of RA maximum is tied to the location of maximum slope than peak elevation of the mountain. Strong diurnal variation is observed in 3-hourly RA which peaks during 12-18 h local time. Anomalous westerlies blow more orthogonal to the barrier during 12-18 h and facilitate a greater terrain-forced upslope flow. Boundary layer (BL) height grows deeper than most peaks in RMZ during afternoon hours resulting in weaker upstream blocking of the low-level winds. This leads to enhanced moist air flow over the summit causing increased RR over RMZ in the afternoon hours thereby enhancing RF and RA.
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