Radar and Disdrometer Observations of Regime-Dependent DSD variability

Understanding the variability of drop size distribution (DSD) parameters has important implications for rainfall estimation from both ground-based and satellite-based radar. For example, if parameters of the DSD, such as mean drop diameter (D₀) and normalized intercept parameter (N_w), vary with meteorological regimes, that information could be used to constrain radar-based rainfall algorithms. Radar and disdrometer observations are used in conjunction with reanalysis data to examine the link between DSD and regime for a variety of locations from mid-latitude continental to tropical ocean and the Amazon. In addition to separation of convective and stratiform elements, disdrometer observed DSD parameters and radar derived DSD parameters are correlated to bulk environmental parameters such as Convective Available Potential Energy (CAPE), warm cloud depth, cloud base height, temperature, dew point and vertical shear. In the mid-latitudes, data from the Mid-latitude Continental Convective Clouds Experiment (MC3E) and Iowa Flood Studies (IFloodS) show the largest correlations are found between convective mean drop diameter (D₀) and warm cloud depth. It is hypothesized this is because a deep warm cloud depth allows hail and graupel to melt nearly completely, resulting in large drops exiting cloud base. Similar correlations are examined using data from the Integrated Precipitation and Hydrology Experiment (IPHEx) in the Appalachians, the TRMM-LBA experiment in the Amazon, and the Dynamics of the Madden-Julian Oscillation (DYNAMO) in the central Indian Ocean. Differences in the environment are proposed to influence the cloud microphysics and subsequently the surface drop size distribution and rain fall.

In addition to direct correlations between DSD parameters and environmental parameters, so-called polarimetric self-consistency between reflectivity (Z_h), differential reflectivity (Z_dr) and specific differential phase (K_dp) is examined as a function of regime. Differences in regime are found as a function of both Z_dr and K_dp/Z_{h_lin}. Linking the DSD variability to polarimetric radar observations, either directly using self-consistency or indirectly by deriving DSD parameters, allows for the possibility of examining cloud microphysical variability world-wide in regions that have polarimetric radar but may not have disdrometer coverage.