Tuesday, 9 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
General circulation models (GCMs) significantly underestimate MAM precipitation over the Amazon basin, especially over the northeast coast (8.75°N to 3.75°S, 58.75°W to 46.25°W). In order to examine what vertical heating profile is needed to simulate realistic precipitation over the Amazon basin and how the Walker Circulation and the Hadley Cell will respond to changes in this profile, heating is added to the northeast Amazon along the coast intermittently during MAM 1998-2010 in the Community Atmospheric Model version 5 (CAM5) using the technique of Lappen and Schumacher (2012). Three experiments have been done including: a control run, an added top-heavy heating sensitivity experiment, and an added bottom-heavy heating sensitivity experiment. Results show that the added top-heavy heating produces more rain over the northeast Amazon, but causes even drier conditions over the central Amazon compared to the control run. The top-heavy heating strengthens the upper branch of the Atlantic Walker Circulation, but leads to enhanced easterlies at mid levels and anomalous westerlies at low levels. The added bottom-heavy heating experiment provides a more practical result: it produces more precipitation over both the northeast coast and central Amazon. It also strengthens the Atlantic Walker Circulation, but enhanced easterlies in the lower troposphere bring more moisture from the ocean to the coast. The added bottom-heavy heating is likely associated with the coastal sea breeze, which cannot be resolved in GCMs with coarse resolutions. The added low-level heating may also have an effect on the strength of the Hadley Cell, affecting weather patterns in the extratropics.
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