SSM/I measured microwave brightness temperature (TB's), anomalies of TB's, and their relationship to typhoon intensification

The SSM/I microwave Brightness Temperatures (TB's) in the frequency domains of 85 and 19 GHz gathered from the Defense Meteorological Satellite Program (DMSP)-F8 satellite form the basis of this research. These data are related to 27 map times of 13 typhoons of the 1987 season, one typhoon of the 1988 season and one cyclone in the Indian Ocean in 1987. The TB's disclosed certain characteristics of typhoons unavailable through conventional infrared (IR) imagery means. Brightness Temperatures were chosen to delineate the typhoon characteristics rather than the derived geophysical parameters such as rainfall or surface winds because the TB's have better resolution. The footprint size of the 85 GHz TB is 15 x 13 km while a derived (through algorithms based on regression) quantity such as rainfall has a much higher footprint size. The relatively large footprint size of rainfall results, because of using the 19 GHz channel which has a larger footprint size of 69 x 43 km. The mean 85 GHz (vertically polarized, V) TB's of a moving typhoon, particularly those on the left side within 55 km of the center, appear to exhibit a practically usable correlation with the 24 hour intensity. This finding is consistent with some observational studies, which show higher rain rates to occur within the asymmetric eyewalls of developing tropical cyclones. Further stratification of the sample in terms of direction of movement improved the correlation The TB anomalies were defined in terms of the TB differences between two sections of a typhoon (e.g., between right and left sides or between inner and outer areas). The development of this sort of anomalies represents a relative growth of deep convection close to the center. If there is a good growth, the cyclone is likely to intensify within a short period of time. The anomalies also showed good correlation with the 24-h intensity. The intensity change (24-h intensity - Current Intensity) was also correlated with the 85 GHz V mean TB values, as well as, with 85 GHz V TB anomalies as defined above. Significant correlations ensued. Since these preliminary results are promising, further experimentation with a larger sample is suggested. Nevertheless, the scientist interested in natural hazards would find the current results valuable in the problem of typhoon intensification.