Development of Convection on the Northeast Region of Brazil, organized by extremities of frontal zones.

Abstract At the extremities of frontal zones, which pass in the Northeastern Brazil (NEB), convection and intense rainfall in some events were developed and, in other fronts, were not. Therefore, the general objective is to analyze the differences in dynamic and thermodynamic processes in these events and to create circulation patterns. Reanalysis data from the global NCEP / NCAR model and satellite infrared images were used for the period of ten years (2000-2009). During the studied period, 103 frontal zones were identified in the NEB. The highest number of the fronts was detected in 2002 and 2007 (14 and 13, respectively) and the lowest in 2004 and 2005 (5 and 6, respectively). Convective activity at the front extremities was formed in 68 events (Group 1, G1) and in 35 events a low active cloud band was identified (Group 2, G2). The thermodynamic was based on the analysis of radiosonde data in the 5 meteorological stations of NEB and instability was evaluated by CAPE and instability indexes K, TT and LI. CAPE and LI showed the greatest differences in G1 and G2. G1 events were found during all seasons of the year, but, more frequently, they were detected during the summer (33 cases), in the cold (19 cases) and hot (14 events) transitions and 1 event in the winter. The G2 events were more frequent during the winter (22 events), 7 events were observed in the cold and hot transitions and none was observed during the summer. Circulation patterns in G1 and G2 were developed at the low, medium and high levels. Synoptic systems of G1 created confluence of currents at the low and medium levels over the NEB, however, in G2, an anticyclonic circulation was observed. The presence of Upper Tropospheric Cyclonic Vortex (UTCV) or an intense trough was typical for G1 at the high levels. Circulation patterns and conclusions about the use of instability indices can facilitate the forecast of the convection development at the frontal extremities.摘要：在流经巴西东北部（Northeastern Brazil, NEB）的锋区末端区域，部分事件中会发展出对流与强降雨，而部分锋面则无此类现象。因此本研究的总体目标为分析此类事件中动力与热力过程的差异，并构建环流分型方案。本研究采用2000—2009年共十年的全球NCEP/NCAR再分析数据与卫星红外影像开展分析。研究期内，于NEB区域共识别出103个锋区：其中2002年与2007年的锋区数量最多，分别为14个与13个；2004年与2005年最少，分别为5个与6个。锋区末端的对流活动共出现在68个事件中（组1，G1），另有35个事件被识别为低活性云带（组2，G2）。热力分析以NEB区域5个气象站的无线电探空数据为基础，通过对流有效位能（Convective Available Potential Energy, CAPE）、K指数、总指数（Total Totals, TT）与抬升指数（Lifted Index, LI）评估大气不稳定性，其中CAPE与LI在G1与G2组间差异最为显著。G1事件全年均可出现，但以夏季最为频发（33例），其次为冷暖过渡期（分别为19例与14例），冬季仅出现1例；而G2事件则更多出现在冬季（22例），冷暖过渡期共出现7例，夏季则无相关事件记录。G1与G2组的环流特征在低层、中层与高层均存在显著差异：G1对应的天气系统在NEB区域的低层与中层形成气流汇合，而G2则呈现反气旋环流；在高层，对流层上层气旋涡旋（Upper Tropospheric Cyclonic Vortex, UTCV）或强槽区是G1事件的典型特征。上述环流分型结果与不稳定性指数的分析结论，可为锋区末端对流发展的预报工作提供参考依据。