Since the late 1970s, scientists have successfully estimated tropical cyclone (TC) central pressure using polar-orbiting satellite passive microwave sounding instruments. These techniques relate a TC's upper-tropospheric thermal anomaly, measured by 55-GHz sounding channels, to its central pressure through hydrostatic balance. The Advanced Microwave Sounding Unit-A (AMSU-A), flown since 1998 on NOAA polar-orbiting satellites, is the first instrument with sufficient horizontal resolution to produce operationally useful estimates. Today, the University of Wisconsin-Madison Cooperative Institute for Meteorological Satellite Studies (UW-CIMSS) produces real-time AMSU-A TC intensity estimates used by the NOAA National Hurricane Center, the Department of Defense Joint Typhoon Warning Center, and international TC forecast centers. The accuracy of these estimates is comparable to the benchmark Dvorak technique, and UW-CIMSS plans to integrate them into a planned multispectral TC intensity algorithm.

While instrument noise and sub-sampling are significant sources of error in the microwave intensity estimates, the largest source of uncertainty is often the scattering of the upwelling microwave radiances by large liquid and frozen hydrometeors. Much work has been done on precipitation rate and integrated water content retrievals using microwave imaging and moisture sounding channels, but comparatively little study has focused on hydrometeor scattering effects on temperature sounding channels. This paper discusses: 1) Rayleigh and Mie scattering theory applied to the liquid and frozen hydrometeors in a TC core and effects on 55-GHz microwave radiation; 2) the modeled 55-GHz scattering signature produced by a plane-parallel atmosphere with varying liquid and frozen hydrometeor profiles and by a 3-dimensional fine-scale TC simulation; and 3) the scattering signatures of observed cases. Future work will apply this scattering signature information to develop and evaluate a statistical scattering correction for AMSU-A radiances employed in the UW-CIMSS TC intensity technique.