Categorizing Ice Crystals Using Airborne APR-2 and HVPS Observations during GCPEx

Abstract:

Current and planned millimeter-wave passive and active satellite sensors are proposed for future low Earth-orbiting satellite platforms. For accurate modeling and sensor simulation of ice clouds at these wavelengths, realistic particle shapes and size distributions (PSD) need to be used. During the Jan-Feb 2012 Global Precipitation Measurement (GPM) Cold Season Precipitation Experiment (GCPEx) near Toronto, Canada, the Jet Propulsion Laboratory (JPL) dual-frequency (Ku/Ka-band) Airborne Precipitation Radar (APR-2) flew onboard the NASA DC-8 aircraft. Coordinated flights were carried out with the Univ. of North Dakota Citation aircraft carrying the High Volume Precipitation Spectrometer (HVPS-3), to collect cloud PSD and particle imagery. Selected flights enabled collection of coincident sampling volumes from the APR-2 and the HVPS. This unique dataset enables the scattering properties of the frozen hydrometeors to be modeled using the HVPS-provided particle distributions, and compared with APR-2 observations.

The wide variety of fractal-like particle shapes measured in the HVPS data were separated into size bins and presented as 2 dimensional histograms with bins defined by Aspect (As) and Area (Ar) ratio. Individual histograms were previously characterized by the mean As and Ar values, ignoring the preferential linear trend between As and Ar visible for data points within most particle sizes. To facilitate the scattering models, we attempted to partition particles by shape within four size-invariant As and Ar categories. The four unique PSD, created by particle shape segregation, were then used to forward model the Ku and Ka- band radar reflectivities to locate the particle characteristics that provided the best agreement with actual APR-2 observations. In future work, these PSD will be used for passive microwave satellite sensor simulations of cold season precipitation and compared to actual satellite observations.