A Z-R Relationship for Hurricanes

Abstract

Drop-size measurements taken during hurricane research flight missions at altitudes at or below 3 km were used to derive a relationship between reflectivity factor and rainfall rate. The instrument used in this study is the Knollenberg Particle Measurement System (PMS) Optical Array Spectrometer Probe, model number OAP-2D-P. The overall Z-R relationship based on data from four flights into three storms at three altitudes is Z=300R^1.35. No important differences were noted when the data were stratified by region (eyewall versus outside of eyewall) or altitude. The importance of using a Z-R relation that is representative of stratiform and convective regimes to estimate precipitation is illustrated by the large extent of the stratiform rain in hurricanes as revealed by radar. Comparisons of the hurricane Z-R relation derived in this study with the classic Marshall-Palmer (1948) relation and the relation used by the National Weather Service for convective rain reveal differences at the high rainfall rates. Comparisons with previous studies of hurricanes and other tropical rain reveal virtually no differences.