Simulations of Cyclone Sidr in the Bay of Bengal with a high-resolution model: Impact of domain sizes

The predictability of Sidr cyclone in Bay of Bengal (India) in terms of track and intensity is explored through simulations using the Advanced-research Hurricane model; a region outside the region of the North Atlantic for which this model was developed and tested. Several experiments are conducted to understand the factors that control Sidr cyclone track by changing (a) initial start time, (b) sea surface temperature (SST) and (c) domain size. The present study suggests that Sidr cyclone track is strongly controlled by synoptic flow at 500 hPa level, in particular strong westerly jets over north-central India. A 96 hour forecast produced westerly winds at 500 hPa level that were too weak over north-central India, which caused the model cyclone track to drift from the observed track. Model error in the synoptic-scale winds at 500hPa can be reduced by reducing the model domain size leading to much improved cyclone track. Specifically, cyclone track appears to be sensitive to the upstream synoptic flow, and therefore sensitive to the location of the western boundary of the domain. However, intensity remains largely unaffected by this synoptic wind error at 500 hPa level. Cyclone intensity is found to be more sensitive to SSTs. Comparison of the high resolution moving nested domain with a single coarser resolution domain shows little difference in tracks but significant difference in intensity.