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Summer Research Fellowship Programme of India's Science Academies

Raindrop size distribution during active and break spells of Indian Summer Monsoon

EZHILARASI G S

Institute of Remote Sensing, College of Engineering, Guindy, Chennai 600 025

DR. SUBRATA KUMAR DAS

Scientist-D, Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan, Pune 411 008 

ABSTRACT

Indian summer monsoon (ISM) rainfall exhibits sub-seasonal variability, with active spells with good rainfall and weak spells or breaks with little to no rainfall. In this work, we investigate the raindrop size distribution (DSD) during the wet (active) and dry (break) spells of the ISM. Investigation of DSD is worthy due to its application in retrieval of rain patterns from weather radar, micro-wave communications, soil erosion and cloud physics etc.

To understand DSD, a Joss–Waldvogel Disdrometer (JWD) has been deployed at the High Altitude Cloud Physics Laboratory (HACPL), Mahabaleshwar (17.92ºN, 73.6ºE, ~1.4 km AMSL) in 2012. The measurement site is in the Western Ghats, located parallel to the west coast of India which receives capacious rainfall (~6000 mm) during the monsoon season (June-September).

In this work, we will investigate DSD during the wet and dry spells of the ISM during the period 2012-2015. The wet and dry spells are identified by using the gridded rainfall data set (1962-2012) over the Mahabaleshwar region. For the study period, the dry periods (159 days) are more compared to the wet periods (41 days). The other rain microphysical parameters like median volume diameter, rain liquid water content and normalized intercept parameter are estimated from the gamma-fit of DSD using the moment method (second, fourth, and sixth moment). An attempt is made to examine the variability in rain parameters during the wet spells and how different it is for the dry spells.

Keywords: Indian Summer Monsoon; Raindrop size distribution; Wet and dry spells; Western Ghats; Disdrometer

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