Impact of bogus vortex for track and intensity prediction of tropical cyclone |
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Authors: | Randhir Singh P K Pal C M Kishtawal P C Joshi |
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Institution: | (1) Atmospheric Sciences Division, Meteorology & Oceanography Group, Space Applications Centre, 380 015 ISRO, Ahmedabad, India |
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Abstract: | The initialization scheme designed to improve the representation of a tropical cyclone in the initial condition is tested
during Orissa super cyclone (1999) over Bay of Bengal using the fifth-generation Pennsylvania State University — National
Center for Atmospheric Research (Penn State — NCAR) Mesoscale Model (MM5). A series of numerical experiments are conducted
to generate initial vortices by assimilating the bogus wind information into MM5. Wind speed and location of the tropical
cyclone obtained from best track data are used to define maximum wind speed, and centre of the storm respectively, in the
initial vortex. The initialization scheme produced an initial vortex that was well adapted to the forecast model and was much
more realistic in size and intensity than the storm structure obtained from the NCEP analysis. Using this scheme, the 24-h,
48-h, and 72-h forecast errors for this case was 63, 58, and 46 km, respectively, compared with 120, 335, and 550 km for the
non-vortex initialized case starting from the NCEP global analysis. When bogus vortices are introduced into initial conditions,
the significant improvements in the storm intensity predictions are also seen.
The impact of the vortex size on the structure of the initial vortex is also evaluated. We found that when the radius of maximum
wind (RMW) of the specified vortex is smaller than that of which can be resolved by the model, the specified vortex is not
well adapted by the model. In contrast, when the vortex is sufficiently large for it to be resolved on horizontal grid, but
not so large to be unrealistic, more accurate storm structure is obtained. |
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Keywords: | MM5 tropical cyclone bogus vortex |
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