Estudo sobre a origem da Corrente de Jato do Nordeste Brasileiro e suas ligações inter-hemisféricas

Abstract

The knowledge regarding the main synoptic systems that affect the weather in the State of Alagoas, in the Northeast of Brazil, would provide information that is fundamental to advancing the understanding and prediction of the weather. The Brazilian Northeast Jet Streams (BNEJSs) are one of the main systems that are related to intense rainfall in Alagoas. Therefore, the aim of this research is to study the origin of BNEJSs and their connections with the Jet Streams (JSs) from Northern Hemisphere (NH) and Southern Hemisphere (SH). A 10-year period, between 2000 to 2009 was chosen for this analyzes. Reanalysis data provided by the National Centers for Environmental Prediction (NCEP), in the level of 200 hPa at 00Z time, were used during this research. An important finding of this research is that inter-hemispheric connections through BNEJSs occurred not only with the participation of the Subtropical Jet Stream (SJS), but also in conjunction with Polar Jet Streams (PJS), meaning that all JSs are able to connect in the process. For the purpose of further understanding the connections among all the JSs, it has been established three circulations patterns of BNEJS: the Meridional, the Tranvsersal and the Zonal. It was observed that the Zonal BNJESs pattern did not connect to all JSs. The most common occurrence pattern is the Meridional CJNEB type, where all the JSs also remained connected longer. In contrast the Transversal pattern was the type with short duration, lasting on average only one day. These three established types of BNEJSs circulation patterns were associated according to the presence of the Upper Tropospheric Cyclonic Vortex (UTCV) or the Upper Tropospheric Trough (UTT). The axis and the position of the UTCV and the UTT were instrumental for the association or separation process of all JSs. Hence, it was noted that the Meridional BNJESs type should present a UTCV or UTT with also a Meridional axis, in order to have the union between all JSs and maintain longer days of connection. Otherwise, the separation or inhibition of connections is more likely to occur. When analyzing the Transversal BNJESs type, it was noted that the axis of UTCV or UTT should also be Transversal to promote the connections between of all JSs. In relation to UTCV or UTT position, it was noticed that the closer they are to the Brazilian Northeast (BNE), the easier will be the establishment of connections between all JSs. Another key finding of this research, was that a unusual event called: Rare Event, was detected – it was observed two particular cases where the connections of all CJs occurred during the Autumn in the SH. Furthermore, it was verified that the origin of the BNEJSs was related to the two Hemispheres - alternating between as a branch of the Northern Subtropical Jet Stream (NSJT) and as the branch of the Southern Subtropical Jet Stream (SSJT).