Multiple-scattering-induced "ghost echoes" in GPM DPR observations of a tornadic supercell

• Published in: Journal of Applied Meteorology and Climatology
• Main Authors: Battaglia, Alessandro, Mroz, Kamil, Tanelli, S., Tridon, Frederic, Kirstetter, P-E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Meteorological Society 2016
• Subjects: Atm/Ocean Structure/ Phenomena; Hail; Tornadoes; Physical Meteorology and Climatology; Convective storms; Observational techniques and algorithms; Radars/Radar observations; Remote sensing; Satellite observations; Leicester; The Spectre; ice core; North Atlantic
• Online Access: http://journals.ametsoc.org/doi/10.1175/JAMC-D-15-0136.1; http://hdl.handle.net/2381/38571; https://doi.org/10.1175/JAMC-D-15-0136.1

Evidence of multiple-scattering-induced pulse stretching for the signal of both frequencies of the Dual-Frequency Precipitation Radar (DPR) on the Global Precipitation Measurement (GPM) mission Core Observatory satellite is presented on the basis of collocated ground-based WSR-88D S-band observations of an extreme case: a tornadic supercell. The ground-based observations clearly show a tilted convective core with a so-called bounded weak-echo region-that is, locations where precipitation is absent or extremely light at the ground while large amounts of liquid or frozen precipitation are present aloft. The satellite observations in this region show reflectivity profiles that extend all the way to the surface despite the absence of near-surface precipitation: these are here referred to as "ghost echoes." Furthermore, the Ku- and Ka-band profiles exhibit similar slopes, which is a typical sign that the observed power is almost entirely due to multiple scattering. A novel microphysical retrieval that is based on triple-frequency (S-Ku-Ka) observations shows that a dense ice core located between 4 and 14 km with particle sizes exceeding 2.5 cm and integrated ice contents exceeding 7.0 kg m-2 is the source of the ghost echoes of the signal in the lower layers. The level of confidence of this assessment is strengthened by the availability of the S-band data, which provide the necessary additional constraints to the radar retrieval that is based on DPR data. This study shows not only that multiple-scattering contributions may become predominant at Ka already very high up in the atmosphere but also that they play a key role at Ku band within the layers close to the surface. As a result, extreme caution must be paid even in the interpretation of Ku-based retrievals (e.g., the TRMM PR dataset or any DPR retrievals that are based on the assumption that Ku band is not affected by multiple scattering) when examining extreme surface rain rates that occur in the presence of deep dense ice layers. The work done by A. Battaglia and F. Tridon was funded by the project “Calibration and validation studies over the North Atlantic and United Kingdom for the Global Precipitation Mission” funded by the United Kingdom NERC (NE/L007169/1). The work done by S. Tanelli was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. This work was carried out for the GPM mission under the Precipitation Measurement Missions program; support by Dr. Ramesh Kakar is gratefully acknowledged. Level-1 V03B-GPM data were downloaded from the Precipitation Processing System. KCRP data were downloaded from the National Oceanic and Atmospheric Administration National Climatic Data Center. This research used the SPECTRE High Performance Computing Facility at the University of Leicester. Peer-reviewed Publisher Version