Impact of physical parameterization schemes on track and intensity of severe cyclonic storms in Bay of Bengal

The objective of the present study is to investigate in detail the impact of different physical parameterization schemes on track and intensity of two severe cyclonic storms, AILA and JAL, which formed over Bay of Bengal, using a WRF mesoscale model. Three 2-way interactive nested domains with horizontal resolutions of 60, 20 and 6.6 km are used with initial and boundary conditions from NCEP-FNL data. Three sets of experiments include sensitivity to cumulus, microphysics and planetary boundary layer parameterization schemes, respectively. From cumulus parameterization experiments, Betts–Miller–Janjic is found to be better in the group. The strength of mid-latitude trough and presence of southward wind surge for cyclone AILA, the strength of the cross-equatorial flow as well as stronger easterly wind fields in the mid-tropospheric levels for cyclone JAL, and the amount of potential vorticity for both cyclones are some of the factors, which affect the large-scale flow and, hence, the track of both storms. WSM6 Microphysics scheme is able to produce a realistic feature of the cyclones as compared to the other schemes. The realistic representation of mid-tropospheric heating contributed by snow and graupel hydrometeors may be one of the reasons for better intensity simulation by WSM6. The higher values of relative humidity in and above the boundary layer favor the deep vertical mixing in YSU and thus contribute towards the better intensity simulation.