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km respectively. The outer domain covers 5°-30° N and 78°-103° E and inner
domain covers 16°-27° N and 85°-91° E. The model follows Arakawa C-grid
staggering and model integration time step is 30 and 10 seconds for outer and
inner domains respectively. Both the domains share the same physics such as
Kain-Fristch convection scheme, Yonsei University (YSU) planetary boundary
layer (PBL) scheme, WRF single-moment 3-class (WSM3) microphysics
scheme, Monin-Obukhov surface scheme, thermal diffusion land-surface
scheme and the Rapid Radiative Transfer Model (RRTM) for long wave and
Goddard for short wave atmospheric radiation schemes. WRF model is proven
for its skillful performance in the simulation of a variety of high impact weather
events, such as heavy rainfall (Bhaskar Rao and Satyaban, 2010; Hong and
Lee, 2009) and tropical cyclones (Osuri et al., 2012; Pattanaik and Ramarao,
2009; Davis et al., 2008) over many parts of the globe. Osuri et al. (2012)
studied the sensitivity of different physical parameterization schemes for the
simulation of tropical cyclones and its application in real time predictions.
Mohanty et al. (2010) studied the sensitivity of different initial and boundary
conditions in tropical cyclone simulations over the North Indian Ocean (NIO)
using WRF model.
There are three land surface models (LSM) available which are coupled in
WRF model. They are the 5-layer thermal diffusion, the NOAH LSM and the
Rapid Update Cycle (RUC) LSM. In a coupled WRF-LSM, the WRF model
provides the surface air temperature, surface pressure, surface specific humidity,
the total cloudiness, U wind, V wind, the precipitation rate, the low cloudiness,
the solar incoming radiation, initial soil moisture and temperature to LSM.
The LSM calculates surface latent, sensible and ground heat fluxes, as well as
soil moisture and temperature profiles, canopy temperature and many other
surface variables, and provides to WRF model as a lower boundary condition
for the vertical transport within the planetary boundary layer (PBL). The LSM
does not provide tendencies of parameters, but simply updates the land surface
state variables including the skin temperature, soil moisture and temperature
profiles, snow cover, and canopy properties.
The severe cyclone “Aila” was simulated from 12 UTC 23 May 2009 to
00 UTC 27 May 2009 (84-hour forecast). It moved northward continuously
throughout its life. Its intensification was rapid and reached severe cyclonic
storm (SCS) stage just before the landfall and crossed West Bengal, India at 09
UTC 25 May 2009 with same intensity (RSMC, 2010). While moving in
northerly direction, the system interacted with land surface and sustained its
intensity for about 15 hours and moved a distance of about 350 km over the
land as a TC. The climatology of the tracks of the cyclonic storms developing
within +/- 2° lat long box of TC Aila location of genesis (i.e., lat. 16.50 N/
long. 88.50 E) on 23 May indicated that any depression formed in this box in
the month of May becomes a cyclone and most of them moved northward/
northeastward towards West Bengal/Bangladesh coasts (RSMC, 2010).
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