Multi-scale analysis of in-cloud vertical velocity derived from 94-GHz Doppler radar (Formerly paper P5B.3)

When present during cold-air outbreaks over warm water, cloud bands represent the organization of the vertical transport of heat and moisture. The continued development of more accurate boundary-layer models examining lake-induced convection therefore requires a better understanding of the vertical velocity structure of cloud bands and their interaction with both larger and smaller scales of motion. As part of Lake-Induced Convection Experiment (Lake-ICE), The Pennsylvania State University 94-GHz vertically-pointing cloud radar was deployed on the downwind shore of Lake Michigan during December 1997 and January 1998. Two lake-effect events, which yielded a total of over 36 hours of data at a temporal resolution of 7.5 seconds, are analyzed. From the Doppler spectrum, we estimate mean vertical air motion within each radar resolution volume from cloud base to cloud top, with a vertical resolution of 30 meters. Dominant frequencies are determined using wavelet analysis, showing a spectral gap between the primary scales of motion. This analysis is performed at each height within cloud, yielding power as a function of frequency and height. Coherence of the vertical velocity at various heights with cloud-base and cloud-top vertical velocity is calculated, as well as correlation of vertical velocity with reflectivity. Conditional sampling and compositing are also used to give insight into the interaction between different scales of motion. For example, it is shown that smaller scale variations in band updraft regions are larger than those in band downdraft regions. The vertical velocity structure of the two events during Lake-ICE are compared to each other, as well as to previously observed lake-effect events.