Radar and Disdrometer Measurements during Superstorm Sandy

During Superstorm Sandy, time series of differential reflectivity (ZDR) from recently upgraded KLWX and KDOX showed two distinct precipitation regimes near 40 dBZ. The disdrometer calculated ZDR at NASA Wallops Flight Facility and Goddard Space Flight Center confirmed the two distinct regimes. The radar and disdrometer based ZDR values observed earlier in the storm were considerably higher than those observed later in the storm. The disdrometer calculated rain rates were lower while the mass-weighted drop diameters were higher during the early part of the storm. These features show the presence of more large drops and less small drops at a given reflectivity during the early stage, which coincided with the passage of a cold frontal system. In contrast, the presence of more small and less large drops during the latter part of the storm coincided with the passage of Hurricane Sandy. The cross over between the two regimes occurred earlier at Wallops than at Goddard as the Hurricane moved northwestward off the Virginia-Delaware shore. It should be noted that the two distinct regimes of ZDR and other rain parameters were observed from both Joss-Waldvogel and OTT Parsivel2 disdrometers. The event composite size distribution from the latter part of the storm had similar structure to tropical storm Lee (2011). This presentation will demonstrate the radar and disdrometer observations during Sandy focusing on the distinct size distribution characteristics and their role in precipitation retrieval algorithms for the NASA Global Precipitation Measurement (GPM) mission.