Case Study of a Winter Precipitation Event using Three 2D-video disdrometers and ARMOR Radar

We present a case study of winter precipitation which occurred on 10 January 2011 in Hunstville, AL. A well- instrumented site is located about 15 km from the ARMOR C-band dual-polarized radar. This site had three 2D-video disdrometers located very close to each other along with other instruments such as for measuring liquid equivalent snow, temperature, wind speeds etc. The emphasis here is on measurement of snow particle size distributions and fall speeds from the three, nearly collocated 2D-video disdrometers which allows for inter-comparison studies and estimates of sampling errors. Using the mean fall speed and shadow area of each particle we theoretically calculate the density versus "apparent" diameter power law from each disdrometer, as well as the liquid equivalent snow (LES) accumulation for the event. We also calculate the LES by matching the time series of the effective radar reflectivity (from the ARMOR radar) with the calculated reflectivity using the snow size distribution from the 2D-video disdrometers along with an adjustable density versus "apparent" diameter power law. The coefficient and exponent of the power law are estimated by the matching procedure as explained previously in Huang et al. (2010). We compare the LES accumulation for the event with a snow gauge located at the instrumented site. We also derive a Ze-LESR power law relation for the event, and a snow accumulation "map" using the ARMOR data.