Diurnal variations in summer season precipitation in India

In the present study, we have analyzed the spatial patterns in the diurnal cycle of precipitation over the Indian subcontinent. We assembled hourly precipitation data for 78 stations spread across the Indian subcontinent for the period 1980 to 2000. On the basis of the results of the first harmonic, we found the presence of a distinct diurnal cycle over most of the Indian subcontinent for frequency, total, and intensity of precipitation events. The standardized amplitudes, indicative of the strength of diurnal cycle over a region, are strongest in peninsular India, with greater than 80% explained variance. The diurnal spatial patterns are broadly a result of the interaction of local orography and convectional processes. The time of maximum precipitation along the west coast is predominantly concentrated a few hours after midnight to predawn hours. The interiors of the subcontinent generally experience late afternoon to early evening showers, which may be attributed to local convective processes. The time of maximum for total amount of precipitation are mostly about half an hour to 1 h before the time of maximum for the frequency. The overall patterns of diurnal cycle were also found to be robust against interannual variations, in the form of ENSO and La Niña years.