Upper Tropospheric Cyclonic Vortex and Brazilian Northeast Jet Stream over Alagoas State: Circulation Patterns and Rainfall

Abstract Interaction between Brazilian Northeast Jet Stream (BNEJS) and Upper Tropospheric Cyclonic Vortexes (UTCV) isn't still well known, as well as its seasonal variability and relation with rainfall pattern. This study's aim is to determine the air circulation patterns in UTCV events with BNEJS in La Niña and El Niño years and its connections with rainfall in the Alagoas State. These connections were analyzed for 9 years between 1988 and 2000 in El Niño, La Niña and Neutral years. NCEP Reanalysis data, rainfall data from 71 meteorological stations and satellite images were used. Fifty-eight percent of 140 observed UTCVs were associated with BNEJS events located in the Brazilian Northeast and 26%, located over the Alagoas State. Three types of BNEJS patterns, denominated as Meridional (M), Zonal (Z) and Transversal (T), have been identified. The M-type BNEJS was the most frequent in Alagoas State, especially in El Niño years. Z and T-types occurred less frequently and were rarely seen in La Niña years. The results showed that in the M-type BNEJS events in 48% of days were not registered precipitation, while Z and T events recorded rainfall in almost 96% of the days.

巴西东北急流（Brazilian Northeast Jet Stream, BNEJS）与对流层上层气旋涡旋（Upper Tropospheric Cyclonic Vortexes, UTCV）之间的相互作用，及其季节变率与降雨格局的关联，目前仍未得到充分认知。本研究旨在明确拉尼娜与厄尔尼诺年中，伴随BNEJS的UTCV事件的大气环流型，及其与阿拉戈斯州降雨的关联。本次分析选取1988至2000年间共9年的厄尔尼诺、拉尼娜及中性年数据，采用NCEP再分析资料、71个气象站的降雨数据与卫星图像开展研究。在观测到的140个UTCV事件中，58%与发生在巴西东北部的BNEJS事件相关，26%的事件则发生在阿拉戈斯州上空。研究识别出三类BNEJS型态，分别命名为经向型（Meridional, M）、纬向型（Zonal, Z）与横向型（Transversal, T）。其中经向型BNEJS在阿拉戈斯州最为频发，尤其在厄尔尼诺年；纬向型与横向型的发生频率较低，且在拉尼娜年极为少见。结果显示，在经向型BNEJS事件中，48%的单日未出现降水；而纬向型与横向型事件中，近96%的单日均有降雨记录。