Características da circulação e da estabilidade atmosférica no Estado do Rio Grande do Norte: aplicação da análise multivariada.

Abstract

The atmospheric conditions in the Rio Grande do Norte State on July 2011 were investigated by applying Principal Component Analysis (PCA) and Cluster Analysis (CA) to observational upper air data. Daily precipitation totals, enhanced GOES-12 satellite imagery and reanalysis data were also used. Four precipitation events were observed in the first half of the month. An intense rainfall event registered on day 16 in Natal accounted for a 60.4 mm daily total in the city. The synoptic ambient was characterized by a low level trough on coastal eastern Rio Grande do Norte and the nearby oceanic area, associated with low level convergence and upper level divergence, and upward motion throughout the troposphere, on the day before the event. The PCA applied separately to data of the 1000, 850, 500 and 300 hPa levels resulted in a three component model for the isobaric levels and synoptic times analyzed. The first factor at 00 UTC is related to moisture, in the low and middle troposphere, and temperature, in the upper troposphere. At 12 UTC the first factor is related to temperature at 1000 and 300 hPa, and moisture at 850 and 500 hPa. The 12 UTC factors time series show a significant increase in moisture in the low troposphere, on the day before the event. The CA applied to the factors obtained by means of PCA resulted in days grouped on the basis of similar meteorological characteristics, for each isobaric level and synoptic time. The application of PCA and CA to atmospheric stability indices grouped the days in accordance with the probability of storm occurrence: one group of difficult interpretation, four groups with low probability and no rainfall in the majority of the days, and two groups with probability and rainfall in the majority of the days.