Abstract
This work examines the sources of moisture affecting the semi-arid Brazilian Northeast (NEB) during its pre-rainy and rainy season (JFMAM) through a Lagrangian diagnosis method. The FLEXPART model identifies the humidity contributions to the moisture budget over a region through the continuous computation of changes in the specific humidity along back or forward trajectories up to 10 days period. The numerical experiments were done for the period that spans between 2000 and 2004 and results were aggregated on a monthly basis. Results show that besides a minor local recycling component, the vast majority of moisture reaching NEB area is originated in the south Atlantic basin and that the nearby wet Amazon basin bears almost no impact. Moreover, although the maximum precipitation in the “Poligono das Secas” region (PS) occurs in March and the maximum precipitation associated with air parcels emanating from the South Atlantic towards PS is observed along January to March, the highest moisture contribution from this oceanic region occurs slightly later (April). A dynamical analysis suggests that the maximum precipitation observed in the PS sector does not coincide with the maximum moisture supply probably due to the combined effect of the Walker and Hadley cells in inhibiting the rising motions over the region in the months following April.
Highlights
Values between 35% and 50% of the annual pluviometric total of the regional precipitation over the semi-arid northeastern region of Brazil (NEB) are observed during the austral autumn rainy season (March to May) [1]
The Intertropical Convergence Zone (ITCZ) is in its southernmost oceanic position in March-April, the maximum precipitation over the studied area occurs slightly before, as it can be seen in the figures 2 and 3, suggesting that there are other mechanisms besides the ITCZ displacement that modulate the precipitation over the region, for instance, some influence of the South American Monsoon System (SAMS)
An analysis of the sources of moisture over the semi-arid Brazilian Northeast (NEB) was performed using the FLEXPART Lagrangian method of diagnosis, focusing on the precipitation variability observed along its pre-rainy and rainy season and the relative importance of the Tropical South Atlantic in providing humidity during this period
Summary
Values between 35% and 50% of the annual pluviometric total of the regional precipitation over the semi-arid northeastern region of Brazil (NEB) are observed during the austral autumn rainy season (March to May) [1]. Water resources in the area suffer as a consequence of the combination of these unusual low values of annual precipitation (for a tropical region) with high values of interannual variability, influenced by several atmospheric and oceanic mechanisms, namely frontal systems, easterly waves, the ITCZ, and modulated by the El Nino and Atlantic signal [6,7,8,9]. This densely populated area is relatively prone to drought episodes, with large socio-economic impact [10]. Despite the growing interest in the region and rising prospects for seasonal predictions [11,12], it is not well known the exact location of moisture sources that affect NEB
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