Casos de windshear nos aeroportos das capitais do nordeste brasileiro

Abstract

The present study contributes to aviation safety and fills a gap in wind shear (WS) research in Brazil, particularly in the Northeast region. The main goal is to analyze the occurrence of WS at the airports of the region’s capitals, to determine the associated weather conditions and synoptic systems. The selected period was two years (January 1, 2017, to December 31, 2018). The cases were chosen based on METAR data of each airport. Present weather and weather radar data on the airports (REDEMET) were also analyzed. Synoptic analyses were performed using data from Reanalysis II (NCEP/DOE, 2.5°×2.5° resolution) and GOES-16 (DSA) satellite imagery. The atmosphere’s vertical structure was examined using data from ERA5 reanalysis (CDS, resolution 0.25°×0.25°), or radiosonde (U. Wyoming), when available. In the studied period, 58 cases of WS were registered, most of them in 2017’s rainy season, specifically in July. The most frequent times were the afternoon and the night hours (between 15-18h UTC, and 23-02h UTC). The most affected airport was Salvador with 35 reports. Natal is second with 10 cases, followed by Fortaleza, João Pessoa and Recife (5, 4 and 2 reports, respectively). Aracaju and Teresina recorded 1 event each, while São Luís and Maceió had no reports. The main active synoptic systems during these cases were frontal zones united or not with the Intertropical Convergence Zone - ITCZ (24 cases), followed by Upper Tropospheric Cyclonic Vortex - UTCVs (11) and Wave Disturbance in Trade Winds - WDTWs (3). The isolated action of ITCZ was diagnosed in single case. The most frequently weather conditions in Salvador were: wind with any easterly component, moderate wind velocity, no gusts and no change in direction, more than 50% of the sky in cloudy, the height of the clouds base at middle levels, the presence of Cumulus Congestus, and precipitation. Visibility was reduced in 15 cases, mist was recorded in four events. Analysis of radiosonde and simulated vertical profiles revealed the predominance of low-level instability in all airports, except Natal, where there was a greater proportion of thermal inversions. The most frequently observed conditions at other airports were different: south winds with gusts and/or change in direction; low-level cloudiness covering up to 50% of the sky, no rainfalls. Horizontal visibility was always greater than 10 km. On the few events where Cumulus Congestus have been recorded, precipitation has also occurred.