Large Eddy Simulation of the diurnal cycle of Shallow Convection in the Central Amazon
Abstract
Climate models often face challenges in accurately simulating the daily precipitation cycle
over tropical land, particularly in the Amazon. One contributing factor may be the
incomplete representation of the diurnal evolution of shallow cumulus (ShCu) clouds. This
study seeks to enhance understanding of the diurnal progression of ShCu clouds—from
formation to maturation and dissipation—over the central Amazon (CAMZ). Using
observational data from the Green Ocean Amazon 2014 (GoAmazon) campaign and large-
eddy simulation (LES) modeling, we investigated the diurnal cycle of ShCu clouds. Our
results reveal a well-defined cycle, with cloud formation between 10-11 LT, maturity from
13-15 LT, and dissipation by 17-18 LT. The vertical extent of the liquid water mixing ratio,
and the intensity of updraft mass flux were closely associated with increases in turbulent
kinetic energy (TKE), enhanced buoyancy flux within the cloud layer, and reduced large-
scale subsidence. We further analyzed the diurnal cycles of convective available potential
energy (CAPE), convective inhibition (CIN), the Bowen ratio (BR), and vertically integrated
TKE in the mixed layer (ITKE-ML), exploring their relationships with cloud base mass flux
(Mb) and cloud depth across six ShCu cases. ITKE-ML and Mb exhibited similar diurnal
trends, peaking around 14-15 LT. However, no consistent relationships were found between
CAPE (or BR) and Mb. Similarly, comparisons of cloud depth with CAPE, BR, ITKE-ML,
CIN, and Mb showed no clear relationships. Smaller ShCu clouds were sometimes linked to
higher CAPE and lower CIN. It is important to emphasize that these findings are preliminary
and based on a limited sample of ShCu cases. Further research is necessary, involving an
expanded dataset and more detailed analyses of the TKE budget and synoptic conditions.
These efforts will offer a more comprehensive understanding of the factors influencing ShCu
clouds vertical development.
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