Salient Observations and Performance Evaluation of Iowa XPOL Radars during the NASA GPM IFloodS Campaign

Abstract:

The University of Iowa network of X-band polarimetric (XPOL) Doppler weather radars comprises of four mobile units with full scanning capabilities. The network has distinct engineering and operational abilities that aid in studying near-ground hydrological processes at smaller scales. During April-June 2013, Iowa XPOLs were deployed for Iowa Flood Studies (IFloodS), the first integrated studies field experiment under the aegis of NASA’s Global Precipitation Measurement (GPM) Ground Validation.

The XPOLs demonstrated their field worthiness with nearly 46 days of near-uninterrupted remote operations in the campaign, and collected research-quality data as indicated by the detailed post-campaign analyses. In this study, we present XPOL observations of selected diverse meteorological events at high spatial and temporal resolutions from a unique and vast dataset generated during IFloodS operations. The XPOL data exhibit detailed, complex structure of precipitation viewed at multiple range resolutions (75 m and 30 m). An inter-XPOL comparison within an overlapping scanned volume demonstrates consistency across different XPOL units.

We derive rain accumulation maps for the XPOL-4 radar data on June 12, 2013 using reflectivity (Z_e) and specific differential phase (K_dp) algorithms derived from scattering simulations using measured drop size distributions (DSDs) from six two-dimensional video disdrometer units from four rain days (data set of 6,200 one-minute averaged DSDs). We constructed Z_e-based rain maps using measured and attenuation-corrected reflectivity. Without attenuation correction the rainfall is vastly under-estimated, whereas the corrected Z_e-based accumulations are more consistent with estimates based on R(K_dp). Still, there are spatial differences between the latter two accumulation maps made apparent due to the high resolution of XPOL-4 used for Z_e algorithm.

For comparison, we derived rain accumulation maps for the same event using the NASA polarimetric NPOL radar except that its spatial (azimuthal) resolution is significantly lower due to long range to the storm complex (>80 km). By comparing the high-resolution rain maps from XPOL-4 radar with 150 m resolution maps from NPOL radar, we are able to examine the scaling properties and observational uncertainties of rainfall.