J. Clim. http://dx.doi.org/10.1175/2011JCLI4189.1 (2011)

Credit: © NASA-JSC-ES&IA

Evaporation over Amazonia provides a source of moisture to the high-rainfall regions of subtropical South America, suggests an analysis of meteorological data.

Josefina Arraut of the National Institute for Space Research, Brazil, and colleagues used weather reanalysis data to study the large-scale transport of moisture over South America between 1989 and 2008. They identify one main pathway of moisture flow to the subtropics, which they refer to as an aerial river: a north-to-northwesterly flow, close to the eastern flanks of the Andes. The data suggest that, during the dry season, evaporation over southern Amazonia contributes to this flow, and therefore to subtropical rainfall.

The researchers estimate that the amount of moisture transported by this aerial river to the subtropics amounts to 10–23 Gt of water per day, equivalent to the daily discharge from the Amazon River itself.