Abstract
In this work we use a Lagrangian model (FLEXPART) to investigate the contribution of moisture from the Atlantic Warm Pool (AWP) to the atmospheric hydrological budget during the period from 1982 to 1999, and to identify which regions are affected by the moisture transport from this source. FLEXPART computes budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day forward trajectories. A monthly analysis was made for May-October, the typical development period of the AWP. Climatologically, the moisture transported from the AWP to North and Central America increases from June onwards. Humidity is also transported towards western Europe from July to October, probably favoured by the positioning of the North Atlantic Subtropical High and its associated flows. The largest moisture sinks associated with transport from the AWP were found from August to October, when the warm pool can extend to the north-western coast of Africa. The technique of composites was used to analyse how the interannual variability of moisture contribution from the AWP depends on changes in the pool’s areal extension, and on the El Nino Southern Oscillation (ENSO). The results indicate that during episodes when the AWP is at its maximum extent, its moisture contribution increased to the Caribbean, to the region of the Inter-tropical Convergence Zone (ITCZ), and to the North Atlantic. By contrast, less moisture was transported to southeastern North America during July and August, or to central North America during September and October. The differences in moisture sink regions for extreme ENSO episodes suggest that there are favoured sinks in the Caribbean and in the ITCZ region during La Nina events.
Highlights
The understanding and quantification of the link between evaporation of water in one region and precipitation in another, and of the connecting processes, is one of the main problems in hydrometeorology (Gimeno et al, 2010)
A joint analysis of the maxima in the precipitation and in the convergence of the vertically integrated moisture flux (VIMF) provides a rough estimate of the positioning of the Inter-tropical Convergence Zone (ITCZ) (Žagar et al, 2011), and (E−P) suggests some moisture contribution from the Atlantic Warm Pool (AWP) toward the eastern Pacific ITCZ region
Higher moisture contributions to continental precipitation occur from June onwards, with sink regions mainly over Colombia, Central America, México, and the eastern United States and Canada
Summary
The understanding and quantification of the link between evaporation of water in one region and precipitation in another, and of the connecting processes, is one of the main problems in hydrometeorology (Gimeno et al, 2010). Moisture contribution from the Atlantic Warm Pool. Applying the same methodology and focusing on tropical latitudes, Drumond et al (2011) studied the moisture contribution of the Western Hemisphere Warm Pool (WHWP) to northern hemisphere precipitation. The WHWP is the world’s second largest warm pool, and is defined by the sea surface temperature (SST) isoline of 28.5◦C (Weisberg, 1996; Wang and Enfield, 2001). At various stages of development, the WHWP comprises the eastern North Pacific and eastern Pacific, the Gulf of Mexico, the Caribbean Sea, and the Western Tropical North Atlantic (TNA). As the WHWP develops, higher SSTs drive a number of linked phenomena: increased temperature and moisture in the local troposphere, decreased sea level pressure (SLP), light winds from the east, and decreased vertical wind shear (Gray, 1968; Knaff, 1997)
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