Multi-sensor analysis of convective activity in central Italy during the HyMeX SOP 1.1

Abstract

Abstract.A multi-sensor analysis of convective precipitation events that occurred in central Italy in autumn 2012 during the HyMeX (Hydrological cycle in the Mediterranean experiment) Special Observation Period (SOP) 1.1 is presented. Various microphysical properties of liquid and solid hydrometeors are examined to assess their relationship with lightning activity. The instrumentation used consisted of a C-band dual-polarization weather radar, a 2-D video disdrometer, and the LINET lightning network. Results of Tmatrix simulation for graupel were used to (i) tune a fuzzy logic hydrometeor classification algorithm based on Liu and Chandrasekar (2000) for the detection of graupel from Cband dual-polarization radar measurements and (ii) to retrieve graupel ice water content. Graupel mass from radar measurements was related to lightning activity. Three significant case studies were analyzed and linear relations between the total mass of graupel and number of LINET strokes were found with different slopes depending on the nature of the convective event (such as updraft strength and freezing level height) and the radar observational geometry. A high coefficient of determination (R 2 = 0.856) and a slope in agreement with satellite measurements and model results for one of the case studies (15 October 2012) were found. Results confirm that one of the key features in the electrical charging of convective clouds is the ice content, although it is not the only one. Parameters of the gamma raindrop size distribution measured by a 2-D video disdrometer revealed the transition from a convective to a stratiform regime. The raindrop size spectra measured by a 2-D video disdrometer were used to partition rain into stratiform and convective classes. These results are further analyzed in relation to radar measurements and to the number of strokes. Lightning activity was not always recorded when the precipitation regime was classified as convective rain. High statistical scores were found for relationships relating lightning activity to graupel aloft.

Hydrometeor classification through statistical clustering of polarimetric radar measurements: a semi-supervised approach

“…The increased presence of the vertically aligned ice could be explained by the reported atmospheric lightning, although a straightforward relation cannot be assumed (Hubbert et al, 2014;Roberto et al, 2016). In terms of vertical ice detection, a comparison with the conventional (fuzzy logic) approach (Fig.…”

Observing relationships between lightning and cloud profiles by means of a satellite-borne cloud radar

“…for temperatures colder than −5 • C), and found that these relationships are relatively invariant between different climate conditions. Roberto et al (2016) found a marked relationship between cloud graupel content by using C-band radar.…”

A Support Vector Machine Hydrometeor Classification Algorithm for Dual-Polarization Radar

“…It is mostly based on [17] and is tailored to identify meteorological targets, with a particular emphasis on the hydrometeors involved in convective events. Recent updates are described in [9,27], for X-band and C-band, respectively, that show the membership functions used. Such functions are not so different from those reported in the literature and therefore the results obtained should not be significantly influenced by the choice of FL classifier.…”

“…Typically, HCAs classify hydrometeors by analyzing the set of dual-polarization measurements pertinent to a single radar measurement volume. Most of the recent literature on fuzzy logic HCA aimed at improving the membership functions (e.g., [7]) also focusing on specific classes [8,9]. Steps forward to improve the robustness of the fuzzy logic approach are the semi-supervised approach in [10], which improved the spatial coherency of classification maps by exploiting measurements in the neighboring bins, and the unsupervised clustering approach [11] to define the number of classes and the membership functions.…”