ARM's disdrometer suite: capabilities and deployment

Description

A disdrometer is an instrument used to measure the drop-size distribution and velocity of falling hydrometeors. Some disdrometers can distinguish between rain, graupel, and hail. ARM is primarily interested in their contribution to the understanding of precipitation processes, but disdrometers can also be used for traffic control, airport observation systems, and hydrology. The latest disdrometers employ microwave or laser technologies. 2D video disdrometers make the most detailed and complete observations of hydrometeor shape and fall velocity.

Impact disdrometers of the Joss-Waldvogel design have been deployed since February 2006 at the Tropical Western Pacific (TWP) Darwin site and since April of 2006 at the Southern Great Plains (SGP) Central Facility. Each typically measures and counts 3.5 million drops annually and does so over the drop diameter range from 0.3 mm to 5 mm. Observations from the impact disdrometers can be found in the ‘disdrometer’ datastream. Five 2D video disdrometers were purchased by ARM with Recovery Act funds from Joanneum Research, and all were deployed in 2011. Four of them are assigned permanently to TWP Darwin, TWP Manus, the SGP Central Facility, and the second ARM Mobile Facility (AMF2). The fifth was used for the Midlatitude Continental Convective Clouds (MC3E) field campaign and is currently at the North Slope of Alaska site in Barrow, testing its ability to characterize snow particles and its performance in Artic cold. ARM’s video disdrometers are able to measure hydrometeor fall velocity, drop height, and drop width of each individual drop observed. Hence, oblateness for each drop can be determined as well. Data are available in the ‘vdis’ and the ‘vdisdrops’ datastreams. The video disdrometers have a measurement range from 0.2 mm to 10 mm.

Lastly, ARM has purchased four Parsivel2 disdrometers made by OTT Hydromet. At the time of this abstract submission, their deployment location(s) had not yet been determined. They are 1D optical disdrometers with capabilities similar to their 2D cousins. They can be easily configured to include hydrometeor classification in the final data product.