Observed and model‐simulated thermodynamic processes associated with urban heavy rainfall events over Bangalore, India

Abstract

A total of 32 rainfall events spanning the period from 2012 to 2014 over the urban Indian city of Bangalore were simulated using the Weather Research and Forecast (WRF) model. Model simulations were carried out with a four‐nested domain initialized with Global Forecast System (GFS) data and the forecast was generated on an hourly basis. The forecasted rainfall at hobli level (Bangalore has 34 hobli divisions with an area of each hobli of the order of about 10 km2) was evaluated in terms of its intensity and pattern of spatial distribution by comparing it with corresponding rain‐gauge observations. Also, the rainfall forecast skill of the model was evaluated statistically by computing root mean square error, bias and mean absolute error. Thermodynamic variables such as equivalent potential temperature, convective available potential energy (CAPE), convective inhibition (CIN), K index (KI), lifted index (LI) and total totals index (TTI) were also derived from the simulated model parameters for all the events and then verified against corresponding observations. The results showed that the WRF model could simulate the rainfall events and associated thermodynamic features qualitatively; however, there were few hoblis where the relative errors in the forecast were > 100%. The forecast errors were relatively lower for cases during the southwest monsoon season compared with other seasons. It was found that the model underestimated thermodynamic indices such as CAPE, dew point depression and the simulated LI were positive; these were indicative of the model's limitation in simulating intense convection and a possible reason for underpredicted rainfall simulations.

A comparison of stability indices and precipitable water derived from radiosonde data collected at two nearby locations and weather radar data in Brazil

“…The stability indices K, LI, TT, SWEAT, CAPE and CIN, and PW were calculated from the vertical profiles of temperature, pressure, and relative humidity collected by the radiosondes (Dong et al, 2018;do Carmo et al, 2019;Guerova et al, 2019;Ajilesh et al, 2020). In the following formulas, the notation used is: T = environmental temperature, TD = dew point temperature, TP = temperature of the parcel, θ = virtual temperature of the environment, θP = virtual temperature of the parcel, f = wind speed, w = direction of the wind, and g = acceleration of gravity.…”

A systematic quantitative review on the performance of some of the recent short-term rainfall forecasting techniques

“…Thermodynamic properties are mainly associated with temperature profile and moisture content determining the convection process (Pall et al 2007;Lepore et al 2015). Thermodynamic indices are important to understand the atmospheric instability, which ultimately triggers the rainfall (Ajilesh et al 2020). Manandhar et al (2019b) stated that for temperate and subtropical regions, an apparent change in PWV values is observed certain hours before the rain.…”

Atmospheric Instability Conditions during Rainy Seasons over Tanzania

“…In Nigeria, it has been found that the seasonal variability patterns of the atmospheric instability parameters and rainfall are similar (Matthew et al 2021). Also, in the tropics, much of the urban heavy rainfall events are enhanced by the organized convection in the lower troposphere, and the atmospheric thermodynamic indices (atmospheric instability indices) which depend on temperature and/or dew point temperature at specific geopotential height levels are important in the determination of such organized convections (Ajilesh et al 2020).…”