Assinaturas de radar polarimétrico de sistemas precipitantes atuantes no Leste do Nordeste do Brasil

Abstract

A Doppler S-Band polarimetric weather radar is an important tool for estimation precipitation and, consequently, for assenssing of meteorolofical systems operating in the region covered by the radar. Currently, we have a radar installed in the city of Parnamirim (metropolitan region of Natal), Rio Grande do Norte, in the East of Northeast Brazil, operated by the National Center for Monitoring and Natural Disaster Alerts (Cemaden). Due to the ability of the radar to estimate precipitation in three dimensions and the physical properties of hydrometeors, this work proposes the following objectives: i) validate the radar estimates with automatic rain gauges, ii) evaluate the polarimetric characteristics of the precipitating systems in the year 2014 and iii) analyze a natural disaster event that occurred in the region using radar data. The study area is centered on the area monitored by radar with a coverage of 181 thousand km2 , which was divided into two sub-regions for a more punctual analysis in which they were defined as R1 (West Region) and R2 (East Region) were defined for presenting different precipitation regimes. For this, data from the polarimetric variables were used: horizontal reflectivity, differential reflectivity, specific differential phase and correlation coefficient extracted from the volumetric sweeps of the radar and data from 4 rainfall stations from Cemaden and INMET that are distributed in the state of Rio Grande do Norte. The data were used in statistical analysis with the generation of representative fields, for example, frequency histograms and vertical mean profiles. The validation of the radar data showed the instrument's ability to estimate the daily precipitation of the regions, presenting an average BIAS of approximately -5 mm/day and an average correlation of 0.74. The radar showed high sensitivity in the warm and mixed phases of the precipitating systems with different top heights of 20 dBZ, in addition to showing that the two regions studied have completely different microphysical signatures, with R1 marked by intense and deep convection, with systems reaching height of 15 km with top of 20 dBZ and R2 marked by stratiform precipitation. This study is the first to use polarimetric radar data to present the microphysical differences of the systems in Northeast Brazil, therefore it represents a significant contribution in the literature.