Climatological Features of the Vento Norte Phenomenon in the Extreme South of Brazil

Abstract

Downslope windstorm known as Vento Norte (VNOR; Portuguese for “North Wind”) is a common phenomenon that occurs in southern Brazil during the winter season. Hence, this study attempted to investigate the climatological characteristics of VNOR using seventeen years (2004–2020) of hourly observations collected at seven meteorological stations distributed over the central region of Rio Grande do Sul State. The VNOR windstorm episodes are identified by intense wind gusts and warm air advection from the northern direction. They were selected from the data set obtained during the winter in the city of Santa Maria (SM). Statistical analysis showed that the detected VNOR events were characterized by mean wind gusts ≈15 m.s-1, mean wind direction of 350° and mean air temperature of 27 °C. Average duration of the events was about 9 h, with the longest event lasting 21 h. Characteristics and effects of this phenomenon were compared with those in other locations (meridional and zonal sections). Average values of wind gusts from the northern direction presented a significant increase of ≈200% for the winter period in SM. Nonetheless, a less significant increase in wind gusts was recorded in the meridional (28%) and zonal (41%) sections away from SM. The central location of SM has favorable topographic characteristics for this amplification, with a sharp altitude difference caused by the plateau- plain interface of ≈300 m. Our findings showed that the VNOR phenomenon mainly affects the climate of the southern region of Brazil, with a local amplification in the city of SM.