Scaling of heavy rainy days with upper air profiles over Chennai during Northeast monsoon

Abstract

This study aims to scale the heavy rainy days (rainfall > 64 mm per day) with the surface and upper-air parameters over Chennai (12.80° N and 80.03° E), located on the east coast of India, during the Northeast (NE) monsoon (October to December) from 2001 to 2015. The daily rainfall and radiosonde observations that are available from India Meteorological Department (IMD), Outgoing Long-wave Radiation (OLR) from Very High Resolution Radiometer (VHRR) Kalpana-1 Indian satellite, and Total Column Liquid Water (TCLW) and vertical velocity from ERA-Interimre analysis are used. The study commences with the comparison of mean daily Integrated Water Vapor (IWV) and rainfall over Chennai. Further, the study proceeds ahead by analyzing the IWV, TCLW, Instantaneous Condensation Rate (ICR) and precipitation extreme efficiency during the heavy rainy days. The results are such as (i) the heavy rainy days are better scaled using IWV and TCLW than with surface air temperature and OLR (ii) ICR during the all heavy rainfall days found high at 700 mb level, and (iii) the precipitation extreme efficiency which is estimated using the ratio of precipitation extreme (obtained from vertical velocity, specific humidity gradient) and the ICR has shown a linear relationship with the surface reaching rainfall through the temporal and spatial smearing of raindrops expected.