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and the AS cyclone Gonu (2-6 June 2007). The model is integrated up to 120
hrs (based on the life cycle of each TC) in a single domain with the horizontal
resolution of 9 km and 51 vertical levels. A total of 16 cases (six initial conditions
for Nargis; five initial conditions for Sidr and five initial conditions for Gonu
cyclone) are considered. Two sets of numerical experiments are carried out
with NMM model. In the first experiment, i.e. in the control (CNTL) simulation,
the initial condition to the model integration is provided from FNL analysis. In
the second experiment, i.e. in the data assimilation (DA) experiment, the
improved initial condition is prepared through 3DVAR assimilation system
using observational data sets from different data platforms like Synop, Temp,
Pilot, Buoys, Airep, Qscat, Ssmi, Kalpana winds. Brief description of the
numerical experiments is provided in Table 2.
Table 2: Initial conditions to the model integration
TC name
ICs for model
Number of
Experiments and
(Intensity)
integration
cases
data used
Gonu (SuCS)
00 UTC 02 June 2007
5
12 UTC 02 June 2007
00 UTC 03 June 2007
12 UTC 03 June 2007
00 UTC 04 June 2007
Sidr (VSCS)
00 UTC 12 Nov 2007
5
Expt 1: FNL (1° × 1°)
12 UTC 12 Nov 2007
Expt 2: DA (9 km × 9 km)
00 UTC 13 Nov 2007
and FNL as FG
12 UTC 13 Nov 2007
00 UTC 14 Nov 2007
Nargis (VSCS)
00 UTC 28 Apr 2008
6
12 UTC 28 Apr 2008
00 UTC 29 Apr 2008
12 UTC 29 Apr 2008
00 UTC 30 Apr 2008
12 UTC 30 Apr 2008
Total number of cases
16
Figure 7 represents the model simulated tracks of the cyclone Gonu with
different initial conditions along with the observed track as estimated by India
Meteorological Department (IMD). The track simulations with DA experiments
are more realistic than that of the CNTL simulations. The spread of the tracks
are comparatively less in the DA experiments than the CNTL experiments.
Similar results (figures not shown) are also noticed for Sidr and Nargis cyclones.
The mean spread of 560 km is found in CNTL simulations, whereas it is only
350 km with DA experiments. The vector displacement error (VDE; km) is
also calculated by taking the best-fit track data as estimated by IMD and the
track position as simulated from different initial conditions for each case.
 
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