Abstract
Previous studies have estimated that 25% to 35% of Amazonian
precipitation comes from evapotranspiration (ET) within the basin.
However, due to simplifying assumptions of traditional models, these
studies primarily focus on large spatial and temporal scales. In this
work we use the Weather Research and Forecast (WRF) regional climate
model with the added capability of water vapor tracers to track the
moisture from Amazonian ET at the native WRF resolution. The tracers
reveal that the well-mixed assumption of simpler models does not hold,
as local ET is more efficiently rained out of the atmospheric column
than remote sources of moisture, particularly in the eastern part of the
basin. Recycled precipitation shows a strong annual and semi-annual
signal, associated with the passage of the Inter-Tropical Convergence
Zone. The tracers also reveal a strong diurnal cycle of Amazonian water
vapor related to the diurnal cycle of ET, convective precipitation and
advected moisture. ET increases from early morning into the afternoon,
some of this moisture is rained out through convective storms in the
early evening, while later in the night strong winds associated with the
South American Low Level Jet advect moisture downwind. Visualizing the
Amazonian water vapor highlights its diurnal beating pattern and
suggests that the Amazon has “younger” water than other regions in the
globe, with very efficient recycling of local moisture.