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in the model. Zhu and Zhang (2006) examined the sensitivity of various cloud
microphysical processes on the hurricane intensity, precipitation and inner core
structure with explicit simulations of Hurricane Bonnie (1998). Their results
indicate that varying cloud microphysical processes show little sensitivity in
hurricane track but prominent departures in hurricane intensity and inner-core
structures. Mc Farquhar et al. (2006) investigated the effects of three different
microphysical schemes on high resolution simulation (2 km) of Hurricane Erin
(2001). Results indicate that the different microphysical schemes caused only
marginal differences in the hurricane track forecast but reproduced notable
differences in the intensity forecast. In this study, sensitivity of mesoscale
simulation of tropical cyclone Aila on different PBL, cumulus convection and
cloud microphysics (CM) is investigated to understand the influence of these
processes on the track and intensity of the storm.
2. Model, Data and Numerical Experiments
The mesoscale model WRF (Version 3.2.1) used in the present study is based
on an Eulerian solver for the fully compressible non-hydrostatic equations with
complete Coriolis and curvature terms. The terrain-following hybrid sigma-
pressure is used as vertical coordinate. The solver uses a third-order Runge-
Kutta time integration scheme and 2 nd to 6 th order advection option in both
horizontal and vertical directions. The grid staggering is the Arakawa C-grid.
A detailed description of the model equations, physics and dynamics is available
in Skamarock et al. (2009).
The initial conditions for the model simulations are derived from the
National Center for Environmental Prediction (NCEP) final analysis (FNL)
datasets available at one degree resolution. The time varying lateral boundary
condition is also derived from the NCEP FNL analysis and updated every six
hours. The topography for the 27 km and 9 km domains of the nested grid
model are derived from the USGS at 10' and 5' resolutions respectively. The
model is initialized at 12 UTC 23 May 2009 and integrated for 66 hours up to
06 UTC of 26 May 2009. The best-fit track data obtained from India
Meteorological Department (IMD) is used for comparison of the model
simulated results.
The sensitivity study is carried out in two stages. In the first, twenty
numerical experiments are conducted with twenty possible combinations of
five PBL and four convections parameterization schemes to find the optimal
combination for the simulation of the cyclone. Other physical processes are
kept fixed along with WSM3 microphysics. The overview of the model used
for the numerical experiments is provided in Table 1. In the second stage,
seven numerical experiments are conducted with seven CM parameterization
schemes which include some single moment (SM) and some double moment
(DM) schemes. The PBL and cumulus convection schemes are kept fixed and
chosen based on the results obtained in the first stage.
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