Caracterização de regimes de umidade em regiões tropicais: comparação entre floresta e savana

Abstract

This study aims to investigate a method to classify humidity regimes based on different "states" characterization of the Tropical Atmospheric Boundary Layer (TABL), both above a forest area and above a savanna area, according with the methodology proposed by Mahrt (1991). Starting this classification, an improvement is performed while incorporates both the analysis of the thermodynamic stability of TABL for a forest area and the variation in Convection Available Potential Energy (CAPE). In these analyses, radiosonde data and data from micrometeorological towers obtained during field experiments have been used, collected during the less rainy period in each area. For the forest area (Caxiuanã) data from the COBRAPARÁ experiment were used (spanning the period from 06 to 13/11 of 2006), while for the savanna area (Daly Waters) data from the “KOORIN” experiment were used (spanning the period from 15/07 to 13/08 of 1974, in Australia). The comparison of humidity regimes of each area suggests that, should the Amazon rainforest be replaced with savanna, this would result in a drier atmosphere, with most of the energy used for the heating of that atmosphere, reduced evapotranspiration, decreased precipitation and the inexistence of CAPE. On the other hand, the analysis of the stability of the atmosphere in Caxiuanã showed that, contrary to observations in the Western Amazon, during the COBRA-PARÁ Experiment, the largest values of CAPE occurred at 18:00 local time due to the humidity convergence that occurs in the bay of Caxiuanã through the land-breeze circulation, indicating that in that area the maximum values of CAPE were associated predominantly with the humidity fields and not with temperature. Under such a “disturbed” TABL conditions, the phase space proposed by Mahrt (1991) doesn’t characterize well moisture regimes associated with great CAPE values.