A Balloonborne Particle Size, Imaging, and Velocity Probe for In Situ Microphysical Measurements

A balloon-borne instrument known as the PArticle Size, Image, and Velocity (PASIV) probe has been developed at the National Severe Storms Laboratory to provide in situ microphysical measurements in storms. These observations represent a largely under-sampled but critical need of microphysics observations for use in lightning studies, cloud microphysics simulations, and dual-polarization radar validation. The instrument weighs approximately 2.72 kg and consists of an HD video camera, a camera viewing chamber, and a modified Parsivel laser disdrometer mounted above the camera viewing chamber.  Precipitation particles fall through the Parsivel sampling area and then into the camera viewing chamber, effectively allowing both devices to sample the same particles.  The data are collected on board for analysis after retrieval. Taken together, these two instruments are capable of providing an unprecedented level of detail in vertical profiles of the size, shape, velocity, orientation, and composition of particles along the balloon path within severe weather.

The PASIV probe has been deployed across several types of weather environments including thunderstorms, supercells, and winter storms. Initial results have demonstrated the ability of the instrument to obtain cutting edge, high temporal and spatial resolution observations of the particle size distributions within convection. A supercell case on 29 May 2012 from the Deep Convective Clouds and Chemistry experiment will be discussed here. The observations from the PASIV are compared against mobile radar observations and some model derived fields from a Lagrangian Analysis. Results indicate that large changes in particle concentrations occur on scales of 10s of meters, indicating a substantial degree of heterogeneity that has previously gone unsampled. Given the detailed particle concentrations sampled, radar reflectivity can be calculated from the measured distribution and broken down into various particle habits and types. In comparisons with mobile radar fields the radar reflectivity tends to be dominated by the presence of graupel, highlighting the need of microphysics parameterizations to properly handle modeled concentrations and assumed particle densities. Furthermore, particle mixing ratios are determined and compared against model derived values.