Dynamic and thermodynamic effects driving anomalous precipitation over Amazon

Abstract

Anomalous rainfall produces droughts and floods over the Amazon region, enhancing risks of forest fires, heatwaves and inundations, which affects the regional fauna, flora, and socioeconomic activities. In this study, the driest and wettest years of the Northern and Southern Amazon are investigated by analyzing the regional moisture and moist static energy budget. For the Northern and Southern Amazon, the dynamic effect, related to vertical movement changes, was the primary cause for the precipitation anomalies. The thermodynamic effect connected with moisture changes also contributed to the Northern Amazon precipitation anomalies. The anomalous vertical motion in the Northern Amazon was mainly caused by the horizontal advection of anomalous moist enthalpy through climatological wind, which alters the moist static energy in the region. Thus, a vertical movement is produced to compensate the energy changes, leading to changes in precipitation. Nonlinear terms and the horizontal advection of climatological moist enthalpy by the anomalous wind constrained the vertical motion in the driest years over Southern Amazon. For the wettest years over Southern Amazon, the anomalous ascending movement had contributions from all moist static equation terms, except the vertical advection of anomalous moist static energy by climatological wind, which had an opposite effect. The latent heat was the main contributor to anomalous moist enthalpy influencing the vertical movement. Further investigations indicated that the tropical Atlantic and Pacific SST anomalies could influence the vertical anomalies. In conclusion, although the dynamic effect (changes in the vertical motion) was the main driver for precipitation anomalies, the thermodynamic contribution related to latent heat anomalies is significant, mainly for Northern Amazon.