Geoscience Reference
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3. Experimental Design, Methodology and Data Used
In the present research work, two sets of experiments have been conducted. In
the first set of experiments, the role of SST representation in the numerical
model has been examined. For this purpose, four different SSTs are used. The
NCEP-NCAR reanalysis skin temperature (hereafter referred to as Control) is
used to conduct the first experiment. In the second experiment, a constant SST
of 27°C is used (hereafter referred as same-SST) at each grid point of the
model domain. In the same-SST experiment, the reason to use a constant value
of SST (27°C) is that it is more than the threshold value (26°C) necessary for
the formation and intensification of the TC (Palmen, 1948; Gray, 1968, 1979;
Emanuel, 1987). In the third experiment, strong SST gradient over three small
regions of Arabian Sea has been incorporated and SST value kept same (27°C)
over the remaining parts of the Sea (hereafter referred to as Inserted-SST-grad).
The SST gradient has put over the same regions where strong positive sea
surface height anomalies (SSHA, averaged over the period from 29 April to 5
May 2002) are present. In the fourth experiment, the SSHA is converted linearly
to SST keeping the gradient same. In this case, the SST values has been kept to
27°C as minimum and 33°C as maximum (hereafter referred to as SSH2SST).
In the second set, two experiments are conducted with two different sets
of SSTs and the range of SST for the first experiment is kept between 27 and
33°C (hereafter referred to as Current SST, CSST) while in the second
experiment, SST is kept between 29 and 33°C (hereafter referred to as Projected
SST, PSST). For both experiments SST is derived from SSHA using linear
interpolation keeping the gradient same with SSHA. The SST that is used to
carry out control, same SST and Inserted SST grad experiments are shown
in Fig. 1.
The NCEP/NCAR reanalysis data is available at 2.5° × 2.5° resolution
(Kalnay et al., 1996) and has been used to provide the initial and lateral boundary
conditions to the model. Except SST, the other geophysical parameters are
provided from United State Geophysical Survey (USGS) data at 10 min
resolution. The SSHA data has been obtained from National Oceanic and
Atmospheric Administration (NOAA) through the web-site www.aoml.
noaa.gov/phod/dataphod/work/trinanes/INTERFACE/index.html. The Joint
Typhoon Warning Center (JTWC) track and intensity data and NCEP/NCAR
reanalysis data have been used to validate the model results.
The MM5 model has been integrated from 12 UTC of 5 May to 06 UTC of
11 May 2002, considering the first 12 hours for nudging to stable the model.
The SST has been provided at the initial time and it is not updated with the
model integration. However the lateral boundary conditions are updated every
six hours.
4. Results and Discussions
The experimental results obtained from the model simulation has been analyzed
into two broad sections namely (A) sensitivity of SST on tropical cyclone and
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