Tropical cyclone wind retrievals using AMSU-A data from NOAA-15

AMSU-A observations from the NOAA-15 polar orbiting satelite are being collected in near-real time during the 1999 hurricane season. This data is being analyzed in a domain that is centered on all Atlantic and Eastern North Pacific basin tropical cyclones using positions obtained from the National Hurricane Center. A retrieval algorithm is applied to the AMSU data to provide temperatures at 40 vertical levels from 1000 to 0.1 hPa. Geopotential height and surface pressure are obtained from the temperatures by integrating downwards from 50 hPa to the surface, where an NCEP analysis is used to provide lateral and lower boundary conditions. These heights are used to calculate gradient winds as a function of radius and pressure. Methods are also being developed to determine the three-dimensional wind field (as a function of latitude, longitude and pressure) from the height field using the nonlinear balance equation. A statistical algorithm to adjust the temperatures to account for attenuation by liquid water is also being tested.

The accuracy of the AMSU-derived winds for the 1999 hurricane season will be evaluated by comparison with aircraft reconnaissance data (primarily in the Atlantic basin). Forecast applications of the wind retrievals will also be discussed.