AIRBORNE ACTIVE AND PASSIVE MICROWAVE OBSERVATIONS OF SUPER TYPHOON FLO

Airborne microwave measurements of precipitation associated with Super Typhoon Flo in the western North Pacific were conducted during Septem ber 16-18, 1990. The sensor package aboard the NASA DC-8 aircraft incl uded a dual-frequency precipitation radar at 10 GHz and 34 GHz and a h ost of radiometers operating at 10 GHz, 18 GHz, 19 GHz, 34 GHz, and 92 GHz, as well as three frequencies near the strong water vapor absorpt ion line of 183.3 GHz. The measurements were made during a few passes over the storm center, and active and passive microwave signatures of the rainbands were detected with a fine spatial resolution. The relati onship between the measured brightness temperature and radar-estimated rain rate is examined at the frequencies between 10-92 GHz. At both 3 4 and 92 GHz this relationship is analyzed with the 10 GHz radar refle ctivity factor measured at altitudes above the freezing layer as a fur ther constraint. The results show that frozen hydrometeors strongly sc atter radiation at these frequencies, especially at 92 GHz. It was sho wn from a close examination of both active and passive microwave signa tures that a significant scattering of radiation at frequencies greate r-than-or-equal-to 18 GHz occurred in the inner eyewall at altitudes o f 3-8 km. This scattering of microwave radiation by hydrometeors in bo th liquid and frozen forms was discussed under our current understandi ng of the scattering mechanism.