Satellite-based tropical cyclone intensity estimation using the NOAA-KLM series Advanced Microwave Sounding Unit (AMSU)

Satellite-borne passive microwave radiometers, such as the Advanced Microwave Sounding Unit (AMSU) on the NOAA polar-orbiting series, are well suited to monitor tropical cyclones (TCs) by virtue of their ability to assess changes in tropospheric warm core structure in the presence of clouds. The temporal variability in TC upper-tropospheric warm anomaly (UTWA) size, structure, and magnitude provides vital information on changes in kinematic structure and minimum sea level pressure (MSLP) through well-established thermodynamic and dynamic principles. This study outlines the aspects of several factors affecting the effective AMSU measurement accuracy of UTWAs, including the practical application of a previously developed maximum likelihood regression algorithm designed to explicitly correct for TC scan geometry and UTWA-antenna gain pattern interaction issues (UTWA subsampling) unique to TC warm core applications. This single-channel AMSU approach (54.96 GHz) is the first step toward a more elaborate multichannel application that is currently under study. Independent application of the single-channel algorithm in the Atlantic and eastern Pacific basins in 2000 and 2001 demonstrates that AMSU-derived UTWAs are moderately correlated with coincident TC MSLP. In addition, further improvements in correlation, and MSLP estimate accuracy, are possible through application of the proposed corrective retrieval algorithm, provided that 1) accurate estimates of TC eye size ( a proxy for the UTWA horizontal dimension) are available and 2) the peak upper-tropospheric warming represented by the AMSU-A 54.94-GHz radiances corresponds with the actual TC thermal structure. This study recommends potential remedies for both of these algorithm skill prerequisites that include the incorporation of improved eye size estimates from ancillary data sources and/or the utilization of additional AMSU-A upper-tropospheric sounding channels.