Tuesday, 8 January 2013
Exhibit Hall 3 (Austin Convention Center)
In South America, southern parts of Brazil are regions particularly prone to severe weather events (high lightning activity, intense precipitation, hail, flash floods, strong winds and occasional tornadoes). Most of the precipitation is associated with extra-tropical cyclones, mesoscale convective systems (MCS), upper level jets and frontal systems. However, MCSs are responsible for a significant amount of the precipitation and severe weather which occur in this area, important for agricultural and electrical energy production for the country. This paper presents results of an analysis of 10 years of radar and lightning data, with the study of radar and electrical characteristics of mesoscale convective systems, considering relationships between the environment where those storms occurred and hydrometeorological observations from Doppler weather radar, lightning detection system and other meteorological observations. For each MCS identified, radar and cloud-to-ground lightning were analysed, specially vertical reflectivity profile and isothermal reflectivity, VIL, lightning flash rate and other characteristics. The daily cycle of MCS occurrence in the radar area indicates a strong diurnal cycle with most of the events occurring late in the afternoon, and this is the same for the electrical activity in the region. The annual cycle indicates more organized MCS during spring and summer. An analysis of the mean vertical reflectivity profile, for the convective area, indicate the strong electrification processes occurring during the MCS life, specially considering observations of reflectivity around the 30dBZ well above the mixed-phase layer in the storms for MCS observed with the radar. The importance of dynamic characteristics in the region, specially the presence of low level jets and humidity convergence in low levels to organize and maintain the MCS events were also observed throughout the analyzed period. The spatial organization of MCS as observed with radar indicate that most of the organized events evolved to a leading line trailing stratiform type of MCS with most of the electrical activity in the convective region. However, the most intense lightning flashes, in terms of peak current estimated by the system, were observed embedded in the stratiform part of the MCS identified in this data set. The objective of this study is to better understand the evolution of these storms as they occur in this area in order to improve our abilities of analysis and forecast of severe weather events.
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