Investigation of precipitation characteristics during NASA GV field projects

Abstract:

The availability of high quality rain gage networks for extended periods of time during NASA ground validation (GV) field projects supporting the Global Precipitation Measurement Mission (GPM) allow for extensive analysis of precipitation characteristics over a variety of locations and meteorological regimes. Changes in drop size distribution (DSD) parameters (e.g. D₀, N_w, LWC) over the course of a six week deployment are shown for the MC3E, IFloodS, and IPHEx experiments. During MC3E, median drop diameters (D₀) progressively increased from late April through mid-May, coupled with a decrease in the normalized gamma number concentration (N_w). The environmental characteristics, such as CAPE, shear and moisture, that are most correlated with this change in DSD are investigated. It is hypothesized that increasing storm strength leads to larger precipitation particles that consume the available water at the expense of smaller particles, leading to increased D₀ and lower N_w. In stratiform regions, stronger storms could lead to enhanced convergence and strong mesoscale ascent, resulting in the growth of larger ice particles and aggregates, also increasing D₀ and lowering N_w.

Changes in DSD are also examined from the perspective of polarimetric radar. The NASA S-band NPOL research radar is used to analyze changes in the DSD using the so-called self-consistency relationship between the ratio of specific differential phase (K_dp) to linear horizontal reflectivity (Z_h) as a function of differential reflectivity (Z_dr). The ability to detect changes in drop size distribution parameters from a high spatial and temporal resolution platform such as a radar would be useful for rainfall estimation. Changes in the self-consistency relationship during MC3E indicate an increase in Z_dr from late April to mid-May, associated with a decrease in the ratio of K_dp/Z_h. The polarimetric data from NPOL are also used to infer bulk microphysics in the column leading to changes in the drop size distribution.