THE MICROPHYSICAL STRUCTURE AND EVOLUTION OF HAWAIIAN RAINBAND CLOUDS.1. RADAR OBSERVATIONS OF RAINBANDS CONTAINING HIGH REFLECTIVITY CORES

Radar reflectivity factors exceeding 60 dBZ are documented within shal low (<3 km), warm (>0 degrees C), summertime tropical rainbands offsho re of the island of Hawaii. Dual-Doppler radar measurements from the H awaiian Rainband Project are used to document the formation, evolution , and kinematic structure of the high reflectivity cores. The authors show that extremely high radar reflectivities (50-60 dBZ) can develop from echo free regions (-20 dBZ) within approximately 15 min and are p receded by 5-9 m s(-1) peak updrafts. High reflectivities (>50 dBZ) ty pically first formed in the middle or upper part of the clouds. Over t he next 10-15 min, the mature high reflectivity cores extended vertica lly through the cloud depth and then collapsed to the surface as the u pdrafts weakened. A near-upright orientation of most updrafts producin g these high reflectivity cores is conceptually consistent with the id ea that large raindrops grow in the highest liquid water content while falling through the updraft core. Strong outflows near the inversion led to the formation of sloped radar echo overhangs surrounding the ce lls. The bases of the overhangs descended to the surface with time, le ading to an overall increase in the width of the rainbands. Short-live d downdrafts were present in the upper part of the clouds in mature an d dissipating stages of cells' life cycles but were not observed in th e lower parts of the cloud, even in intense precipitation shafts.