The impact of assimilation of MODIS data for the prediction of a tropical low-pressure system over India using a mesoscale model

Abstract

A low-pressure system formed over the Bay of Bengal, India on 15 October 2003 and crossed the east coast of India during the late hours of 17 October 2003. The system, which provided copious rainfall over the Bay of Bengal and stations on the east coast, is investigated in this study using the fifth Generation Mesoscale Model (MM5). Three sets of numerical experiments are designed in this study. While the first set utilizes National Center for Environmental Prediction - Aviation (NCEP-AVN) analysis (for the initial conditions and lateral boundary conditions) only in the MM5 simulation, the second set utilizes the vertical profiles of temperature and humidity obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) (as well as a few radiosonde station data) to provide an improved analysis. The third set used the vertical profiles of temperature and humidity from MODIS alone to provide an improved analysis. The results of the three sets of simulation are compared with one another as well as with the analysis and observations. It is found that the predicted sea level pressure of the MM5 simulation which utilized the improved analysis: reproduces the large-scale structure of the low-pressure system as manifested in the NCEP-AVN analysis; provides a stronger and deeper low-pressure system as seen from the sea level pressure field; and shows a larger northward extent of the associated precipitation pattern as compared with the simulation with just the analysis. The results of the third experiment (impact of vertical profiles of temperature and humidity using MODIS alone) compare well with the results of the second experiment except that in the former, the associated cyclonic circulation in the lower troposphere appears weaker. The results of this study, although restricted to a single case study, demonstrate that inclusion of MODIS derived vertical temperature and humidity profiles together with radiosonde data caused a favourable impact on the simulated structure of the low-pressure system.