Mesoscale Convective Systems Observations with Polarimetric Weather Radar and Total Lightning in the South of Brazil - A Nowcasting Challenge

The operational routine in weather monitoring and forecasting has changed a lot in the past years. Besides conventional information, well known in operational centers, data from remote sensing such as satellite, weather radars and lightning detection network provide vital information in real time, as the main tools for severe weather detection and forecasting.

In South America, especially northeastern Argentina, Paraguay and Southern Brazil are regions particularly prone to severe weather (mainly intense precipitation, hail, extreme lightning incidence, gust winds and occasional tornadoes). In the south of Brazil, monthly precipitation distribution is very uniform throughout the year, mostly related to Mesoscale Convective Systems (MCS) forming in this area. The major economical activity in this region is agro-industry and energy production (responsible for more than 35% of hydro-power energy used in the country) directly dependent on precipitation distribution and water availability.

Mesoscale Convective Systems (MCS) play an important role on the hydrological cycle and on the incidence of severe weather events, highlighting the importance of improving the knowledge of those weather systems, with the goal of better forecast. They are observed in this area during all the year, associated with low level jets with strong wind shear and humidity in the lower atmosphere, but are most common in the warm season. They are responsible for more than 80% of the precipitation in the region and the lightning incidence. Previous studies show that they also are responsible for most of the positive polarity and high current peak lightning discharges in thee region. This is still to be investigated with this new approach.

This paper presents an initial analysis of warm season MCS occurrence in a region monitored with a S-Band polarimetric weather radar and a network of total lightning (intra-cloud and cloud-to-ground) sensors used to identify the electrification processes within these storms and their relation with radar signals, specially polarimetry. Storms are tracked with TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting) algorithm to identify their development stage and to evaluate how the polarimetric signatures compare and change during the evolution of the MCS in the monitored area. This research is one of the few recent efforts to understand the electrification processes of the MCS using polarimetric radar and total lightning information and most certainly one of the first in subtropical region of the world. With this work we expect to contribute to the understanding of MCS structure and evolution of electrification processes as observed and detected by polarimetric radar and total lightning detection system, and to improve the comprehension and ability to analyze and forecast such severe weather events in an operational environment.