Parsivel2 disdrometer inter-comparison study in support of MAGIC

Description

Observations of cloud and precipitation are primary goals for the Marine ARM GCPI Investigation of Clouds (MAGIC) field campaign, currently underway. Vertically pointing cloud radars are critical tools for this research. Typical radar calibration methods rely on collocated scanning cloud radars. A scanning radar will not be available during MAGIC; hence, the decision was made to deploy optical disdrometers to monitor and to try to constrain the quality of the radar data. From the available suite of ARM disdrometers, the Parsivel2 disdrometers manufactured by Ott Messtechnik were thought to have the chance to accurately measure rainfall and/or drop-size distribution under admittedly difficult conditions. Because no absolute calibration is available for the disdrometers, a side-by-side inter-comparison study is being carried out at Brookhaven National Laboratory to evaluate Parsivel2 precision and feasibility to provide relative calibration for the cloud radars. In part the inter-comparison is intended to determine the influence of ship motion on observed drop distributions and the equivalent reflectivity factor calculated from those distributions. A preliminary analysis of the data suggest that the minute-to-minute results of the disdrometers can be used to predict equivalent reflectivity factor to +- 1.5dBZ and +-2.5 dBZ for W- and K-band observations, respectively. Any attempt to use the results of the side-by-side study to as a basis for determining the precision of equivalent reflectivity factor as measured on ship must take into account two important caveats. First, the ship moves at a steady 10 meters/second and often experiences higher wind speeds. Those conditions cannot be recreated in the current side-by-side disdrometer inter-comparison. Secondly, the disdrometers and the radars have very different sampling volumes.