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Fig. 2:
Difference (BOG - CNTL) in the initial condition due to bogusing seen in
surface pressure (hPa) (top row) for the case of (a) Laila on 19
th
May 2010, (b) Giri on
21
st
Oct 2010 and (c) Phet on 2
nd
June 2010. Panels in the bottom row show vertical
cross section of difference (BOG - CNTL) in meridional winds.
experiments (BOG - CNTL) for surface pressure which varies from -8 hPa to
-1 hPa for Laila (and -4 hPa to -0.5 hPa for Giri and -6 hPa to -1 hPa for
Phet). In all the three cases it is evident that the difference is negative indicating
a reduction in surface pressure due to bogusing. Panels in bottom row show
vertical cross-section of change (BOG - CNTL) in meridional wind (m/s) where
the latitude is fixed at the observed location of the cyclone. For all the three
cases a positive (
negative
) change in the meridional winds to the east (
west
)
indicates enhanced southerly (
northerly
) component due to bogusing. It can be
noted that the impact of bogusing can be seen to extend up to 10 km in height.
Thus,
TC bogusing not only reduces the surface pressure near the centre of the
cyclone but also enhances the cyclone circulation and vertical structure for all
the three cases.
Similar analysis is also carried out for VAR-CNTL (not shown).
However, the impact was rather poor. Both CNTL and VAR experiments failed
to show the genesis of cyclones in the IC.
3.2 Impact on forecast tracks
Based on model runs with multiple IC, forecast track errors are computed for
each model run against the best track data from the IMD. The average track
error for each cyclone case is presented in Fig. 3. (Fig. 3a for cyclone Laila Fig
3b for Giri and Fig. 3c for Phet). Similarly average track errors are obtained in
each of the experiments. The forecast in the CTNL experiments shows large
track errors. In the BOG experiments, the case of Laila shows highest
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