Transporte de umidade nos regimes monçônicos e sua variabilidade relacionada com eventos de seca e cheia na Amazônia

Abstract

Atmospheric moisture transport and moisture convergence characteristics of the monsoon regimes of the globe are obtained. Special emphasis is laid on the South American monsoon system. The NCEP/NCAR gridded analysis data for 62 years is used for the calculations. Seasonal cross-equatorial moisture transport in the sector of a given monsoon regime is seen to characterize the monsoon intensity. Whereas the lower tropospheric winds change their direction by almost 180 ° from winter season (DJF) to summer (JJA) over the South Asian and East African monsoon region, the trade winds over the tropical Atlantic and tropical South America east of the Andes remain basically easterlies in all seasons. However, the moisture transport across the equator in the South American monsoon region changes sign from JJA to DJF, being north to south in the DJF season. The mean yearly total cross-equatorial moisture transport from the Southern Hemisphere to Northern Hemisphere is approximately three times the discharge of water by the mighty Amazon River into the Atlantic, most of it happening in the Indian Ocean. Between the equator and 20ºN there is moisture convergence, which supplies moisture for the ITCZ. This explains its position to north of the equator. A comparison of different monsoon regimes reveals that the South Asian monsoon is wide and three times more intense than the South American monsoon. The Australian monsoon is weaker than the South American monsoon. There is an indication that the South American monsoon is stronger, on seasonal average, when the Australian monsoon is weaker. The convergence of moisture accounts for almost 70% of the total rainfall over the Amazon Basin, the remaining 30% is contributed by evapotranspiration over the Amazon forest. The sources of moisture for the Amazon Basin are situated in the Tropical North and South Atlantic Oceans away from the equator but equatorward of 35ºS and 35ºN. Moisture transport from the Tropical South Atlantic into the Amazon Basin passes over Northeast Brazil. However, there is net divergence of moisture over the Northeast. The regression showed a not very good relationship between the moisture convergence and precipitation over the Amazon basin in the wet season (October to April), where approximately 34% of the rainfall variability is explained by variability in moisture convergence over the basin. The level of the Rio Negro has a low correlation with the moisture convergence over the basin being 26% in DJF. The results of this study indicate that the atmospheric moisture transport can be used to identify the monsoon and characterize its intensity