Impact of Radiance Data Assimilation on Simulation of Tropical Cyclone Thane Using WRF-3DVAR Modelling System - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 379

errors in initial conditions. One way to improve the initial values is the data
assimilation method.
It is a special focal point how to utilize a variety of observational data,
especially unconventional observations over data sparse region to improve the
accuracy of TC prediction. The use of satellite observation, among them, is
now being of great importance in that it could provide a larger covering area,
even distributive and higher spatial resolution atmospheric information and
increase the observational information for the wide zones of ocean, plateau
and desert with few conventional observations. Several previous studies have
demonstrated that the inclusion of satellite-derived winds near and around the
centre of the storm can substantially improve the initial analyses of TCs and
hence the prediction of track, intensity and structure (e.g. Chen, 2007; Pu et
al., 2008). Osuri et al. (2011) have demonstrated that the assimilation of Special
Sensor for Microwave Imagery (SSM / I) and Quik Scatterometer (QSCAT)
satellite-derived observations collectively could bring out the realistic track
intensity, structure and rainfall of TCs over the NIO with many different TC
cases using Weather Research Forecasting (WRF)-3D variational assimilation
(3DVAR) system. Zhang et al. (2007) have shown the impact of multi-satellite
data on initialization and simulation of Hurricane Lili's (2002) rapid weakening
phase. The inclusion of the retrievals improved the forecast skill of numerical
weather prediction models. However, the retrieval problem is mathematically
ill-posed. Consequently, retrieval errors are complicated to understand and
specify correctly in the assimilation systems. In recent years, the attention has
now been focused on methods through which the information in the radiance
measurements are assimilated more directly into the NWP models. Assimilation
of radiances requires radiative transfer model to compute very rapid calculations
of top of atmosphere radiances for a range of space-borne infrared and
microwave radiometers viewing the earth's atmosphere and surface. Almost
all the operational NWP centres now routinely assimilate satellite radiance
data.
Hence, a study has been undertaken to assess the impact of radiance data
obtained from NOAA series satellite on track, intensity, structure and rainfall
of TC over the BoB. In this study, the high-resolution non-hydrostatic mesoscale
model, Advanced Research WRF (ARW, hereafter WRF) modelling system
and its 3DVAR system are used. In this context, a very severe cyclonic storm
(VSCS) Thane (26-30 December 2011) is considered in this study.
2. Synoptic Situations
A well marked low pressure area concentrated into a depression and lay centred
at 1200 UTC of 25 th December 2011 near lat. 8.5°N and long. 88.5°E.
Continuing its north-northwestwards movement, the deep depression intensified
into a cyclonic storm 'Thane' at 1800 UTC of 26 th December 2011 near lat.
11.0°N and long. 87.5°E. It then moved west-northwestwards and intensified