Radar observations of humidity variability in and above the marine atmospheric boundary layer

Abstract

Examines variability in humidity at the top of the marine atmospheric boundary layer and in the overlying free troposphere, using data collected during the marine stratocumulus phase of the First Regional Experiment (FIRE) of the International Satellite Cloud Climatology Program. Doppler wind reflectivity data were used to derive a time series of the humidity structure function parameter. Rawinsonde data provided a time series of specific humidity, and vertical gradient of specific humidity. Correlation analysis confirmed the theoretically expected relationship. The correlation was greatest in the inversion region where vertical humidity gradients were the greatest, regions of high correlation being associated with a line of zero height lag between the two instruments. The time series of radar derived entrainment rates agree qualitatively with features of the marine inversion structure that are evident in the contoured humidity data, suggesting that clear air backscatter intensity data could be used to help deduce humidity structure and entrainment. (C.J.U.)