Abstract
In the present study, seven-year-long observations of rain microphysical properties are presented using a ground-based disdrometer located at Braemore; a site on the windward slope of the Western Ghats (WG) over the Indian Peninsula. The annual cycle of rainfall shows a bimodal distribution with a primary peak during summer monsoon and secondary peak during pre-monsoon. Pre-monsoon rain events are less in number but are with high intensity and characterize large raindrops and low number concentration. During summer monsoon, short and less intense rain events with small drops are noticed. Post-monsoon rain is having a long duration less intense events with lower concentration of large raindrops compared to the summer monsoon. In the seasonal variation of mean diameter (Dm) and raindrop concentration (NT) with Rain Intensity (RI), winter and pre-monsoon rains exhibit higher values of Dm and lower values of NT compared to the summer and post-monsoon seasons for all the RI ranges. The mean features of the rain microphysical parameters are also supported by the case studies of rain events. RI, Dm and NT are categorized into different range bins for all the seasons to identify their variation and relative rainfall contribution to the total seasonal rainfall. Heavy drizzle/Light rain has maximum rain duration, and the relative contribution to the rainfall is high from heavy rain type. Winter and pre-monsoon rains are mostly contributed from the larger raindrops (>Dm3), and during summer and post-monsoons it is from Dm2 onwards. The distribution of occurrence frequency of NT and rainfall are similar during all four seasons. NT2 recorded rainfall percentage nearly the same as NT1 in summer monsoon and this also supports large number of raindrops in this season. In RI-Duration analysis, all seasons showed similar distribution, and 90% of total duration is contributed from RI with less than 20 mm h−1.
Highlights
Cloud microphysical processes play vital roles in the genesis and modulation of stratiform/convective rain, especially over mountain regions
Copious rainfall is available in this mountain slope during the summer monsoon in addition to thunderstorm seasons and the rainfall is minimum during the winter season
In the seven year study period, the station registered a total rainfall of 9264.77 mm from 3551 rain events, which consists of total duration of 1299.3 hours
Summary
Cloud microphysical processes play vital roles in the genesis and modulation of stratiform/convective rain, especially over mountain regions. Observational evidences indicate that shallow organised and extended orographic convective cloud structures may occur at intermediate heights of mountain ranges[18] These convective organisations have substantial impacts on regional rainfall and can strongly influence the long-term trends, especially in the mountainous regions. The fall speed of raindrops is directly proportional to the height of the topography and this topography influences rainfall kinetic energy in order to impact the soil[31,32] All these demand more work on details of rainfall events and the microphysics of rain such as raindrop size, fall speed and RI distribution at high altitude sites to identify the soil loss during rain to reveal the underlying processes. Statistical parameters like maxima, mean and standard deviations (SD) are computed for the microphysical parameters (RI, Dm and NT) of rainfall and observed considerable variations in these parameters
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