Snow Study at CARE

Data used in this study were obtained at the Centre for Atmospheric Research Experiments (CARE) between 2005 and 2006 during the Canadian CloudSat/CALIPSO Validation Project (C3VP) period with a Hydrometeor Velocity and Shape Detector (HVSD) and a vertically pointing X-band radar (VertiX). VertiX measures the time evolution of reflectivity structure in the vertical, while HVSD provides information on shapes, sizes and fall velocities of freely falling precipitation particles. The latter was calibrated with simulated drops, and it measures the velocity of particle more accurately than size showing 5 % of uncertainty in velocity measurements compared with 10 % in size.

We first analyzed a snow case of 25th Nov. 2005. The temperature at the ground was approximately -9 °C, decreasing with height to -38 °C at 4 km. Particle images recorded by the HVSD revealed them to be aggregates with holes and rough surfaces of the particles. In addition, the shape of the curve for the unrimed aggregates was similar to the curve measured here when velocity-diameter curves were compared with that of Locatelli and Hobbs. Based on these facts, we conclude that aggregation can occur with temperature as low as -9 °C.

Doppler spectra from VertiX spread widely as well as showing zigzag patterns indicating the existence of strong turbulence. Our study shows the possibility that rapid snow growth (~10 dB/km) rate can be induced by turbulence.