Numerical Simulation of Hurricane Bonnie (1998) Using the Advanced Microwave Sounding Unit Derived Winds

Tropical cyclones normally form over the open oceans where the in-situ measurements are difficult to obtain. To simulate and forecast the hurricane, one often introduces a bogus vortex based on the observational information of eye location, maximum wind, minimum sea-level pressure. The actual asymmetric distribution of the low-tropospheric wind field is not taken into account in the bogused vortex although it strongly affects the movement and development of the hurricane.

In this study, we simulate Hurricane Bonnie (1998) using the atmospheric wind field obtained from the Advanced Microwave Sounding Unit A (AMSU-A) aboard NOAA-15 satellite. The AMSU-A provides the 15 channel measurements at the microwave spectrum from 23.8 to 89.0 GHz. A three-dimensional temperature field is first retrieved with a horizontal resolution of 50 km. A hydrostatic approximation is made to convert the temperature field to the geopotential. The atmospheric wind field is then derived by solving the gradient-wind balance equation which relates the geopotential to the stream function. An asymmetric structure is successfully obtained in both horizontal and vertical directions.

The evolution of Hurricane Bonnie is then simulated with a mesoscale model, i.e., the Penn State-NCAR non-hydrostatic, two-way interactive, movable, triply nested grid mesoscale model with the finest resolution is 4 km. In order to get a quick spinup, a new vertical velocity nudging scheme is used in the hurricane initial deepening stage. A model integration is made up to 120 hours covering the rapid deepening, quasi-stationary stages and landfall near the coast of North Carolina. The model can simulate the hurricane track, intensity and inner-core structures reasonably well due to the use of satellite AMSU derived wind data and CAMEX3 data. More simulation results are being presented at the meeting.