No abstract

Coupled ocean-atmospheric phenomenon such as tropical cyclones (TC's) is governed by geophysical fluid dynamics. TC associated strong wind stress transfer momentum energy to the ocean surface that acts as the prime mechanism in modulating the sea surface and in generating the storm surge. A primitive equation, Princeton ocean model (POM) with free surface, sigma (terrain-following) coordinates and realistic bottom topography is configured in Bay of Bengal (BoB) to simulate the storm surge/sea surface height (SSH) and surface currents during a super cyclone TC05B 1999. TC wind fields are developed by adopting a suitable formulation based on partial conservation of angular momentum. Modeled TC wind fields are superimposed with QuikSCAT Satellite/National Centre for Environmental Prediction (QSCAT/NCEP) blended ocean surface winds to drive the three-dimensional ocean model. Model simulated storm surge and SSH are compared with limited available surge estimates/observations and multi-satellite observed AVISO (Archive, Validation and Interpolation of Satellite Oceanography) SSH, respectively to evaluate its performance.

Tropical cyclones (TC's), while moving over the ocean bring about significant changes in ocean thermal structure and other ocean environment. These oceanic thermal responses provide vital information for understanding the air-sea interaction processes. This study used Princeton Ocean Model (POM) to investigate the changes in the oceanic thermal characteristics of Bay of Bengal (BOB) associated with TC05B (Orissa super cyclone) 1999. Model was forced with the wind and heat plus salinity fluxes as surface forcing in different experiments. In order to provide reasonable and realistic cyclonic winds to the model as forcing, the tropical cyclone wind model (TCWM) was developed to generate the synthetic cyclonic winds and superimposed with the analyzed blended QSCAT/NCEP wind field. Results show significant drop in sea surface temperature (SST) beneath the storm centre and to the right of the track confirming the earlier findings and are in qualitative agreement with the available Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) satellite SST imageries. Subsurface thermal structures also reflect significant impact of cyclonic vortex over BOB.

Tropical cyclones form in oceanic regionswhere cool and humid air lies above warm and deep water. With an unstable atmosphere and a fairly weak vertical wind shear, therising thermal heatover the water can continue moving upward while the humidity causes deep clouds to form. As the warm air continues to rise, it strengthens thecirculation of the system, which is induced by the earth's rotation.The resulting strong winds, along with torrential rainsand subsequent flooding that are caused by thisatmospheric phenomenon arecapable of causing severe loss to both life and property. To mitigate the potentially devastating effects of tropical cyclones in an area, the risk of their occurrence must first be assessed. This can be effectively accomplished through the use of catastropherisk models for tropical cyclones,given the availability of quality data as well as an advanced scientific understanding of the structure and formation of these storms.Comprehensive catastrophe risk modelsthat effectively assess tropical cyclone risk consist of three basiccomponents. First, a hazard component assesses the tropical cyclone risk and intensity in an area. A large catalog of stochastic tropical cyclone events is generated by simulating tracks and characteristics based on historical data. This information is incorporated with local physical features to determine the intensity of the simulated events at property locations. Second, an engineeringcomponent estimates the damage on property due to perils associated with these events such as strong winds and precipitation-induced flooding. The engineering component uses the local intensity determined by the hazard component tocalculate damage estimates to buildings and their contents based on exposure data. Finally, afinancialcomponent computesloss estimates based on the damageoutput, while incorporating the appropriateinsurance terms and conditions.Tropical cyclonemodelshave proven to be greatly useful to emergency planners, the insurance industry, and disaster management in India as they effectivelyaddress many important questions concerning risk. These questions includethe return period of tropical cyclone lossesin a given location,as well as an assessment of the likely frequency and severity of storms. The insight that these models provide is also greatly enhanced by an accurate and up-to-date geographical distribution of properties in the area