PARSIVEL

Marine ARM GPCI Investigations of Clouds (MAGIC): Parsivel Disdrometer support for MAGIC

1 October 2012 - 30 September 2013

Lead Scientist: Pavlos Kollias

Observatory: AMF, MAG

Retrievals of cloud and precipitation properties during the MAGIC campaign relied critically on the calibration of the AMF2 radar systems. For MAGIC this included the KAZR and M-WACR, both fixed zenith-pointing systems, and the 1290 MHz beam steerable wind profiler. Calibration methods rely on the zenith pointing cloud radars being co-located or within close proximity of a Scanning ARM Cloud Radar (SACR). The scanning systems are calibrated by periodically viewing corner reflectors of known size and distance from the radars. When the scanning systems are viewing the same cloud volumes in space and time as the vertically pointing systems, cross-calibrations can be performed. The AMF2 SACR was not deployed during MAGIC and therefore calibration of the zenith pointing cloud radars was not possible using standard procedures. As a means to monitor and provide constraints on the calibration of the radars a disdrometer was deployed on the ship during MAGIC. The AMF2 has a 2-dimensional video disdrometer (2DVD) but this system was considered impractical for ship deployment (calibration and vibration concerns). Accurately measuring rainfall on ships, and even more so drop size distributions, was challenging due to ship distortions of the wind flow (e.g. Yuter and Parker, 2001). This was particularly true in strong winds which were common during MAGIC due to the ship cruising speed and the prevailing winds along the ship track. Ship vibrations were problematic for impact disdrometers as were the rather large vertical motions (heave) of the ship expected during MAGIC (+/- 1 to 2 m/s being common). Based on discussions with many ASR scientists and review of what literature is available, the Parsivel optical disdrometer appeared to provide a good choice for measuring drop size distributions required to calibrate the ARM radars.