Cross Validation of Hail Signature from Ground Radar and GPM-DPR

Following the successful Tropical Rainfall Measurement Mission (TRMM), on February 2014, NASA and JAXA jointly launched the Global Precipitation Measurement (GPM) Core Observatory, as a part of the GPM mission. The Dual-Frequency Precipitation Radar (DPR) on board the GPM core observatory operates at two frequency channels - 13.6 GHz (Ku-band) and 35.5 GHz (Ka-band), as opposed to the single Ku-band frequency of TRMM Precipitation Radar (TRMM-PR). Compared to TRMM, GPM offers a wider global coverage (65^oN – 65^oS). The addition of Ka-band channel along with its high sensitivity mode, gives GPM-DPR better sensing capabilities. Thereby, DPR helps in observing light rain and falling snow (that accounts for significant fractions of precipitation in mid and high latitudes).

The addition of Ka-band in GPM-DPR can help in a better understanding of the hail in convective storms. The DPR, enables us to study the difference in reflectivity measurement at the two frequencies – measured Dual-Frequency Ratio, DFRm. The vertical features of the DFRm profiles have been used in the classification module of level-2 DPR algorithm (Iguchi et al. 2010). Previous studies have shown the evidence of the occurrence of multiple scattering in the DFRm vertical profiles in certain hail cases (Battaglia et al. 2014). The vertical profiles of reflectivity at Ka-band shows anomalous features that cannot be explained by single scattering theories.

Cross validation of the precipitation observations from space-borne radars with the dual-polarized ground radars is important (Chandrasekar et al. 2008). This study focuses on cross validation of hail signatures from DPR observations with simultaneous dual-polarized measurements from ground radars for numerous cases during May 2015 - July 2016. The ground radars chosen here are the dual-pol WSR-88D (NEXRAD) across various locations from the continental United States. These ground radar data are chosen such that the inner swath of the GPM-DPR, has had a good overpass within their 100 km range and that they are closest in time with the DPR overpass. Hydrometeor classification is performed for ground radars and cross compared with DPR results (Bechini et al. 2015). The comparison is used to evaluate the hail identification from DPR and the results are presented.

REFERENCES:

Battaglia, A., Tanelli, S., Heymsfield, G.M., and Tian, L., 2014: The Dual Wavelength Ratio Knee: A Signature of Multiple Scattering in Airborne Ku-Ka Observations. J. Appl. Meteor. Climatol., 53, 1790-1808, doi: 10.1175/JAMC-D-13-0341.1

Bechini, R., and Chandrasekar, V., 2015: A Semisupervised Robust Hydrometeor Classification Method for Dual-Polarization Radar Applications. J. Atmos. Oceanic Technol., 32, 22–47, doi: 10.1175/JTECH-D-14-00097.1

Chandrasekar, V., Hou, A., Smith, E., Bringi, V.N., Rutledge, S.A., Gorgucci, E., Petersen, W.A., and Jackson, G.S., 2008: Potential Role of Dual-Polarization RADAR in the Validation of Satellite Precipitation Measurements – Rationale and Opportunities. Bull. Amer. Meteor. Soc., 1127-1145, doi: 10.1175/2008BAMS2177.1

Iguchi, T., Seto, S., Meneghini, R., Yoshida, N., Awaka, J., and Kubota, T., 2010: GPM/DPR Level-2 Algorithm Theoretical Basis Document, 72 pp. [Available online at https://pmm.nasa.gov/sites/default/files/document_files/ATBD_GPM_DPR_n3_dec15.pdf]