Features of the upper tropospheric cyclonic vortices of Northeast Brazil in life cycle stages

Abstract

AbstractThe main purpose of the study is to explore in more detail the Upper Tropospheric Cyclonic Vortices (UTCVs) features over Northeast Brazil (NEB) in an attempt to improve weather forecasts. The various aspects of the life cycle features of the UTCVs over NEB are presented here, because these aspects have not been investigated in previous studies. Initially, the UTCVs were identified at 200 hPa, and then, they were identified at lower levels to analyse their vertical structure, using 6‐hr data for a 30‐year period (1984–2013) from the European Center for Medium Range Weather Forecasts' reanalysis (ERA Interim). An objective method was improved to obtain at first‐hand the trajectory and the vertical extent of the UTCVs over NEB. Some statistics results were consistent with previous studies related to relative frequency, duration and direction of movement. However, further results were obtained too. An average distance of 2,000 km for the UTCVs total travel was found. Of this average distance, 750 km was reached by UTCVs on the first day of the life cycle, leading to the presumption of a possible suppression of vortex movement that depends on a diabatic mechanism. We also found predominance of UTCVs without vertical tilt or with east tilt with increasing height. When considering life cycle stages (formation, maximum depth and dissipation), diversity was observed in intensity with stages, levels and seasons of the year, with spring exhibiting the most intense UTCVs over all seasons. Finally, our finding about interannual variability is novel. There was a tendency for the average number of UTCVs to be slightly higher during El Niño summers compared with La Niña summers.