We studied rainfall characteristics of Brazil for the period 1979–2011. This is an update for an earlier study with data from 1958 to 1978. We compared the three consecutive wet and dry months in the two data sets. In the northern most part rainy season earlier was in April to July and now it is occurring later. In a large part of the south central region the rainy season in austral summer and dry season in austral winter did not change. However, to the east of this region rainy season in the latter data occurs earlier. Calculation of linear tendencies showed, that over the northern Amazon region there is a significant increase of rainfall. This agreed with previous results. Over this region dry season is becoming drier and wet season wetter. In the west of Northeast Brazil (NEB) there is an increase of rainfall. In southeast Brazil there is a region of highly significant decrease of rainfall in both wet and dry seasons. This is confirmed in our analysis on river discharges in Sao Paulo and Minas Gerais states. The negative tendencies in rainfall have great impact on the hydroelectric generation not only in this region but also at the national level because the hydroelectric dams furnish energy on a national level. The increase in rainfall in Northern Amazon is probably associated with Atlantic warming that resulted in higher moisture transport from east. The decrease of rainfall in southeast Brazil seems to be associated with the plummet of rain producing systems from south due to increase of mean sea level pressure in the south.

In an attempt to validate the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) over Brazil, TRMM PR estimates are compared with rain gauge station data from Agência Nacional de Energia Elétrica (ANEEL). The analysis is conducted on a seasonal basis and considers five geographic regions with different precipitation regimes. The results showed that TRMM PR seasonal rainfall is well correlated with ANEEL rainfall (correlation coefficients are significant at the 99% confidence level) over most of Brazil. The random and systematic errors of TRMM PR are sensitive to seasonal and regional differences. During December to February and March to May, TRMM PR rainfall is reliable over Brazil. In June to August (September to November) TRMM PR estimates are only reliable in the Amazonian and southern (Amazonian and southeastern) regions. In the other regions the relative RMS errors are larger than 50%, indicating that the random errors are high.

No abstract

Seasonal variations in the Southern Hemisphere (SH) storm track characteristics and associated wave propagation are studied using 19 years of NCEP-NCAR gridded data. It is found that the SH storm track is strongest in the austral autumn season and weakest in spring. The characteristics of wave packets are studied by computing 1-point lag correlation maps with unfiltered meridional wind at 300 hPa. It is found that the eastward group velocities of waves are much higher than the phase velocities in the transition seasons. This shows that the downstream development occurs throughout the year and is a basic feature of upper-tropospheric waves in the midlatitudes of the SH. This extends previous studies made for winter and summer seasons. Based on the indices that show wave coherence and correlation maps, it is found that the pathways in the transition seasons split into two branches east of Australia, in a way similar to what happens in the zonal wind distribution.

Tropical Easterly Jet (TEJ) of summer monsoon over the north Indian ocean is weakening in recent years. The absolute easterly shear shows a strong negative correlation (significant at 99.9% level by students' two sided t‐test) with the number of severe storms suggesting that a decrease in easterly shear is favorable for the formation of more severe tropical storms. For the first time in recorded history a category 5 Hurricane formed in June 2007 together with two more severe tropical storms over the north Indian ocean. Thus if the present decreasing trend of TEJ intensity continues there is a strong likelihood of the formation of tropical cyclones of hurricane intensity even during the summer monsoon. Presently these intense systems are known to form only in the pre and post monsoon seasons, when the vertical wind shear is small.

The relationships between coastal upwelling and local winds at Cabo Frio (Brazil) are studied using SST and time series of surface wind for a ten-year period (1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979)(1980).The results showed that the seasonal variations of SST and local winds are closely related.Sea-breeze circulation is intensified by the enhancement of land-sea temperature gradient due to cold water upwelling near the coast and coastal upwelling in turn is associated with strong northeasterlies. This confirms the conclusions of earlier modelling studies.Interannual variability is also apparent in the results. INPE ePrint: sid.inpe.br/mtc-m17@80

A primitive equations global zonally averaged climate model is developed. The model includes biofeedback mechanisms. For the Northern Hemisphere the parameterization of biofeedback mechanisms is similar to that used by Gutman et al. (1984). For the Southern Hemisphere new parameterizations are derived. The model simulates reasonably well the mean annual zonally averaged climate and geobotanic zones.Deforestation, desertification and irrigation experiments are performed. In the case of deforestation and desertification there is a reduction in the surface net radiation, evaporation and precipitation and an increase in the surface temperature. In the case of irrigation experiment opposite changes occurred. In all the cases considered the changes in evapotranspiration overcome the effect of surface albedo modification. In all the experiments changes are smaller in the Southern Hemisphere.

Large precipitation deficits observed during the 2001 austral summer over the southeast region of Brazil contributed to the worsening of the energy crisis that was occurring in the country, with unprecedented social and economic consequences. Reliable information on the beginning of the rainy season was essential for the Brazilian government to manage the energy crisis. The purpose of this study is to determine the rainy season in this region and to point out the risk of using outgoing longwave radiation (OLR) data to estimate the beginning of it. The results show that when OLR data are used the beginning and the end dates of the rainy season are wrongly anticipated and delayed, respectively. The present study aims to provide useful information for the management of the impact of adverse climate conditions such as the one in 2001 by basing the analysis on rainfall data instead of on OLR.