Predicting Present and Future Drought
Abstract

Abstract Author: Edward K. Vizy and Kerry Cook

Abstract Title: Influence of the Amazon/Orinoco Plume on the Summertime Atlantic Climate

Abstract: The Amazon is the world’s largest river in terms of average discharge, and the Orinoco is the third largest. Together they account for more than 25% of the global freshwater discharge to the ocean. These warm, fresh plumes create a barrier layer that stabilizes the near-sea-surface water column and inhibits vertical mixing. Because of this stabilization, SSTAs associated with the river discharge persist at the surface and advect into the open ocean. These anomalies have magnitudes on the order of 1 K and are most prominent during the boreal summer and early boreal fall.

The purpose of this study is to understand the basic hydrodynamics of the plume’s influence on the atmosphere as an external forcing problem, and to examine the implications for regional climate features, including rainfall, the Caribbean low-level jet (CLLJ), and the Great Plains low-level jet (GPLLJ). Idealized regional climate model simulations using WRF are conducted to explore the influence of the plume SSTAs on the large-scale climate variability. The first-order structure of the response to the plume SST forcing is the Gill/Matsuno response, which is associated with a weakening of the CLLJ over the Caribbean Sea and its extension into the Eastern Pacific associated with a weakening of the high pressure over the Gulf of Mexico and Caribbean Sea, and a northwestern shift of the North Atlantic anticyclone. Model results suggest that the spatial extent of the response is dependent on the basic state background conditions. Regions where the plume SSTA forcing results in wetter conditions are the tropical eastern North Pacific, the east coast of Mexico from Texas to the Bay of Campeche, and the southeastern United States. The south central United States and north central Mexico tend to be drier when the Amazon/Orinoco plume forms.