Abstract
The term “friagem” is used to define the decrease of air temperature in tropical latitudes; however, most of the studies associate it with the arrival of a cold front in the northern region of Brazil. In this context, the study aims to show that in the Central-West region also occur “friagens”. For this reason, a methodology based on daily maximum temperature is presented. The frequency of “friagem” episodes (1961-2012) in the city of Cuiaba (MT) was determined, and finally a synoptic classification of the surface circulation associated with these events was presented. The results show that “friagens” are associated with daily maximum temperature declines above 10 °C that can occur on the day of arrival of the cold front in Cuiaba or one day after. During the study period, 217 cases of “friagem” were identified, which are mostly associated with four synoptic patterns, which represent 74.6% of all “friagem” cases in the Central-West of Brazil. The most frequent synoptic pattern shows a post-frontal anticyclone that moves from the South Pacific Ocean toward the continent, favoring a strong cold air advection over the central portion of Brazil. However, three other synoptic patterns are important for the “friagens” in the Central-West of Brazil, which are related with cold fronts, blocking situations on the Atlantic Ocean and cyclogenetic events in southern Brazil, respectively.
Highlights
Circulação Atmosférica em Superfície Associada às Friagens no Centro-Oeste do Brasil Gustavo Carlos Juan Escobar; João Caetano Mancini Vaz & Michelle Simões Reboita
The authors showed that the most typical pattern related to cold events in South America is the presence of a large ridge in mid-levels over the Paciic Ocean near the coast of South America and that is associated with an intense surface post-frontal anticyclone favoring cold air advection from the south
The purposes of this work are to identify “friagem” events in Cuiabá, with a methodology based on maximum temperature, and the principal modes of atmospheric circulation at surface associated with these events
Summary
“Friagens” (locally known term) are deined as cold surges that invade the tropics and afect the Amazon (Marengo et al, 1997) producing a great impact on the population due to the decrease of the air temperature and humidity (Oliveira et al, 2004). Marengo et al (1997) mention that the intensity of the “friagens” is associated with the magnitude of the changes in the weather conditions caused by the penetrating cold air. The goal is to identify the maximum temperature decrease and the magnitude of this decrease associated with the passage of the cold fronts in Cuiabá (Figure 1) to characterize the “friagem” events For this reason, we selected 23 synoptic charts with cold front occurrence over Cuiabá in the period 2007-. To verify if the daily decline of the maximum temperature is associated with a cold incursion, the maximum temperature in the “friagem” day must be signiicantly below the mean climatological maximum temperature ( Max) for a speciic period of the year (Escobar and Bischof, 2001) For this reason, it was calculated both the mean climatological maximum temperature ( Max) and standard deviation (σ) for each month from April to November in Cuiabá. To determine these numbers of components, the eigenvalue 1.0 rule was used (Richman et al, 1992)
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