Relação entre duração dos eventos de el niño com as condições do atlântico tropical e conseqüências sobre o regime de precipitação no Ceará durante a estação chuvosa

Abstract

The Intertropical Convergence Zone (ITCZ) reaches its southmost position in March - May, following the annual cycle of the sun. Dry (wet) years on Ceará are caused by an anomalous positioning of the ITCZ to the north (south) of its climatological position drove by sea surface temperature (SST) variations. A SST of 27,5˚C seems to be the threshold for the convective activity, above that convective activity is mainly competitive between regions of highest SST, available to become part of a continuous ITCZ. The SST interannual variability on the tropical Atlantic is modeled by many internal and external factors of the basin. One of them is the positive SST anomaly in the central and eastern equatorial Pacific along with changes in the atmospheric circulation known as El Niño – Southern Oscillation (ENSO). This phenomenon differs from others because of its strong influence over other oceans via teleconnections, including the Atlantic conditions. This study is focused on how El Niños of different durations (events that lasted until February are classified as short events, and the ones that lasted after February are classified as long events) affect the conditions on the North Atlantic, and what is the response on Ceará in terms of rainfall. The results of geopotential height anomalies composites show the existence of a positive Pacific-North American (PNA) pattern during both short and long duration El Niños, however larger wind divergence anomalies along with a weaker North Atlantic Subtropical High and weaker trade winds from the northern hemisphere are noticed in the long duration El Niño composites. This causes a reduction of the wind-evaporation-SST feedback, leading to positive SST anomalies in the Tropical North Atlantic. The individual analysis of the El Niño events shows that 89% of the long duration El Niños resulted in a positive Atlantic interhemispheric SST gradient and 78% of these Atlantic conditions brought drought to Ceará. On the other hand, 33% of the short duration El Niño resulted in a positive Atlantic interhemispheric SST gradient with also 33% of drought conditions.