Abstract
Abstract During the cold season, episodes of a windstorm known as Vento Norte (VNOR) are frequently observed in the city of Santa Maria, situated in the central region of Rio Grande do Sul (RS). The onset of this windstorm is characterized by strong gusts with northerly component which are accompanied by a sharp increase in temperature and abrupt drying. A methodology based on the observed behavior of the standard deviation of temperature during VNOR was successful in identifying the onset and demise of the windstorm. Additionally, the research shows the results of different micrometeorological variables during the event. Early morning and evening atmospheric profiles exhibit an elevated mixed layer over central RS in association with the strong VNOR winds, indicating the presence of mechanically-forced mixing during nighttime hours.
Highlights
Understanding the characteristic scales of motion present in the Planetary Boundary Layer (PBL) and their interactions with larger-scale phenomena is crucial for the correct description of the transport of scalar and vector quantities occurring between the surface and the atmosphere
The criteria that characterize the occurrence of an Vento Norte (VNOR) event have been modified concerning that suggested in (Chamis and Nascimento, 2012) which were based on hourly data from the automatic station of the Institute of Meteorology (INMET) located in Santa Maria at 10 m in height
In the period between 17:30 and 22:30 LST of the first day, the wind speed decreased (U ∼ 3 m.s−1), this value is still high when compared to the average (U ∼ 1.5 m.s−1) observed in the morning preceding the episode of VNOR (02:00 to 09:00 LST)
Summary
Understanding the characteristic scales of motion present in the Planetary Boundary Layer (PBL) and their interactions with larger-scale phenomena is crucial for the correct description of the transport of scalar and vector quantities occurring between the surface and the atmosphere. Among the wind systems that can alter the regular diurnal cycle of turbulence and temperature in the PBL, are the topographically-induced circulations. Meteorological observations of the VNOR phenomenon intense, especially on the downslope side of elevated terrain features (Decker and Robinson, 2011; Karmosky, 2019; Elvidge and Renfrew, 2016; Durran, 2015; Whiteman, 2000) These wind systems, or windstorms, disturb the local conditions in such a way that induce anomalies in the atmospheric variables that can depart significantly from the regional climatology for a given time of the year and/or time of the day (Elvidge and Renfrew, 2016; Math, 1934; Brinkmann, 1971; Norte, 2015; Raphael, 2003; Mass and Ovens, 2019; Smith et al, 2018, Liu et al, 2020). These phenomena can last for several hours and even days, and are known for the hazards that accompany them, such as thermal discomfort, damage to residential roofs, natural fires, reduced animal and plant production, among others (Sartori, 2003)
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