Estrutura vertical das frentes frias durante a passagem do Sul até o Nordeste brasileiro, entre 2000 e 2012

Abstract

This study aimed to analyze the changes in the vertical structure of cold fronts that hit the state of Alagoas between 2000 and 2012. To find the best fields for the analysis of fronts at low latitudes and set vertical patterns as the system shifts to the equator, vertical sections of the variables wind, vorticity, temperature and equivalent potential temperature were studied on 4 fixed observation points (Porto Alegre, Sao Paulo, Salvador and Maceió) and others where there is regeneration and cyclogenesis. We analyzed 18 cases of frontal systems that directly influenced the state of Alagoas, ranked nebulosity presented in the first observation point (Porto Alegre) in Type I: classical cold front, with cloud cover on the continent and ocean; Type II: Cold front end with causing little or no cloud cover over the continent; Type III: Cold front associated with other types of cloud cover over the continent: IIIA: cold front associated with convective cloudiness over the continent and IIIB: cold front associated with jet stream of cloudiness; Type IV: secondary cold front and Type V: cold front with cyclogenesis in the southeast (not going through Porto Alegre). The frontal systems reached Maceió all year: type I ranged between autumn and winter; type II only in the fall; type III, mainly in the southern spring, with cases in winter and summer; type IV only in winter and type V in transitional seasons. The regeneration and cyclogeneses influenced the arrival of frontal systems at low latitudes. The fronts were identified by classical synoptic method, satellite and horizontal wind fields and equivalent potential temperature using reanalysis of the European Centre for image data (ECMWF), infrared channel satellite images of the CPTEC/INPE and Alagoas precipitation data SEMARH -AL. At lower latitudes, the only variable able to register the front surface to high levels was the equivalent potential temperature. The cases have been changed in their structures coming to the last observation point with just three types of cloudiness: Type I; Type II and Type IIIA.