Diurnal cloudiness in Rio Grande do Sul State, Brazil: climatology and temporal tendency

Abstract

The climatology of the meteorological elements, that is, the calculation of average of long state period, variability, extremities and frequency or probability of occurrence, has a great importance and applicability in several activities, mainly in agriculture. The objective of this paper was to study a decadal and monthly climatology of the diurnal cloudiness index (DCI) and annual and season temporal tendency in the State of Rio Grande do Sul. For this, a decadal and monthly sunshine duration data from 17 weather station widely distributed in the State were used for 1960 to 2005 period. The results show that for both decadal and monthly distribution, on average, June, July, August and September had presented the highest of DCI and the months with lowest values were January and December. The west-northwest region of the State presents the lowest DCI and the east-northeast presents the highest. The highest diurnal cloudiness indexes occur during the winter while the lowest values occur during the summer. The index of diurnal cloudiness in the state of Rio Grande do Sul, from 1960-2005, had significant tendency by increment for the year, in the autumn and in the summer.