Thermodynamic Characteristics Associated with Heavy Rainfall over Uttar Pradesh and Bihar

Abstract

Uttar Pradesh (UP) and Bihar mainly experience flood due to heavy rainfall during July and August. The probability of detection heavy rainfall over this region by the India Meteorological Department (IMD) is about 50-60%. This is mainly due to the fact that heavy rainfall over these regions occurs due to meso-scale forcings of convection in a large scale synoptic environment. In this study an attempt has been made to find out potential thermodynamic predictors for occurrence of 24hours heavy rainfall over these meteorological sub-divisions during July and August. The upper air radiosonde and radiowind (RS/RW) data during 2001-2005 for month of July and August have been used for this purpose. While heavy rainfall over Bihar and west UP is uniquely related with higher than normal thermodynamic indices of K-index (KI), total totals index (TTI), vertical totals index (VTI) and cross totals index (CTI) over Patna and Gwalior respectively, the heavy rainfall over east UP is related with higher than normal TTI and CTI over Gorakhpur and KI, VTI and CTI over Patna. Above normal (by about 10-15%) relative humidity at different levels up to troposphere over Patna, Gorakhpur and Gwalior stations favours occurrence of heavy rainfall over Bihar, east UP and west UP respectively.

The mean CAPE associated with heavy rainfall over Bihar is greater than 1900J/Kg over Patna. Heavy rainfall over east UP is associated with mean CAPE of greater than 1900J/Kg over Gorakhpur and heavy rainfall over west UP is associated with mean CAPE of greater than 2800 J/Kg over Gwalior respectively. CINE less than 30J/Kg, 40 J/Kg, 60 J/Kg over Patna, Gorakhpur and Gwalior are associated with heavy rain fall over Bihar, east UP and west UP respectively. While Patna and Gwalior have uniquely higher values of CAPE and kinetic factor for heavy rainfall over Bihar and west UP respectively, Gorakhpur does not exhibit so for heavy rainfall over east UP.