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Easterly Jet (TEJ) intensity continues there is a strong likelihood of the formation
of tropical cyclones of hurricane intensity even during the summer monsoon.
Among all these factors, the thermodynamics and air-sea interactions are closely
associated with the physical processes in numerical models. Therefore, physical
parameterisation schemes have a significant impact on the accuracy of forecasts
of hurricane intensity and movement (Li and Pu, 2008). Chan et al. (2004)
found strong convective asymmetries for four tropical cyclones that made
landfall over Hong Kong. Such asymmetries cause potential vorticity tendencies
and thus affect vortex motion. The objective of the present paper is to foresee
the best possible combination of physics for the simulation of tropical cyclones
in terms of cumulus convection, planetary boundary layer, micro physics and
land surface processes.
2. Data and Methodology
The model used in the present study is the time tested weather research and
forecasting model (WRF ARW) which consists of fully compressible non-
hydrostatic equations, and prognostic variables including the three-dimensional
wind, perturbation equations of pressure, potential temperature, geo-potential,
surface pressure, turbulent kinetic energy and scalars. It has a terrain following
vertical coordinate and Arakawa C-grid staggering in the horizontal. For the
present study the model is configured with a two-way interactive nested
domains. Two domains one with an outer domain (64.52 E-103.87 E, 1.5 N-
31.03 N) of 27 km and one with an inner domain (73.51 E-96.2 E, 5.1 N-27.5
N) of 9 km have been used. The initial and time varying boundary conditions
and the sea surface temperature for the model domains have been interpolated
from NOAA NOMADS data available at 1 × 1 degree resolution. The model
topography and land cover for the 27 and 9 km domain regions are obtained
from the USGS 5, 2 and 30 data sets. The intensity and the movement of the
simulated cyclones are compared to the India Meteorological Department
observations. The model configuration is given in Table 1.
Synoptic Situation of Cyclone Aila
A severe cyclonic storm (SCS) Aila
crossed the West Bengal coast near Sagar
Island between 1330 and 1430 hrs IST of 25th May 2009. It continued to move
in a northerly direction across West Bengal and caused loss of about 100 human
lives and left several injured. It also caused about 175 human deaths and left
several injured in adjoining Bangladesh. The special features of this storm are
as follows:
(i) The system moved in a near-northerly direction throughout its life period.
(ii) Its intensification was rapid only a few hours before landfall.
(iii) The system maintained intensity of the cyclone even upto 15 hours after
the landfall.
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