Abstract
Ocean variability is a dominant source of remote rainfall predictability, but in many cases the physical mechanisms driving this predictability are not fully understood. This study examines how ocean mesoscales (i.e., the Gulf Stream SST front) affect decadal Southeast US (SEUS) rainfall, arguing that the local imprint of large‐scale teleconnections is sensitive to resolved mesoscale features. Based on global coupled model experiments with eddying and eddy‐parameterizing ocean, we find that a resolved Gulf Stream improves localized rainfall and remote circulation response in the SEUS. The eddying model generally improves the air‐sea interactions in the Gulf Stream and the North Atlantic Subtropical High that modulate SEUS rainfall over decadal timescales. The eddy‐parameterizing simulation fails to capture the sharp SST gradient associated with the Gulf Stream and overestimates the role of tropical Pacific SST anomalies in the SEUS rainfall.
Plain Language Summary
Current global climate models (GCMs) typically fail to fully resolve mesoscale ocean features (with length scales on the order of 10 km) such as western boundary currents, which potentially limit rainfall predictability over decadal timescales. Improvements in high‐performance climate modeling enable us to incorporate high‐resolution ocean models (0.1°) that capture these important mesoscale features with increased fidelity. Here we show that the inclusion of mesoscale ocean processes produces a more realistic Gulf Stream and improves both localized rainfall patterns and large‐scale teleconnections. The high‐resolution model shows a better representation of the air‐sea interactions between the sea surface temperature and low‐level atmosphere over the Gulf Stream, thus improving low‐frequency rainfall variations over the Southeast US. The results further imply that high‐resolution GCMs with increased ocean model resolution may be needed in future climate prediction systems.
Key Points
Decadal rainfall pattern and associated mechanism in the Southeast US are examined from an eddying global coupled model
Eddying CCSM4 improves the air‐sea interactions in the Gulf Stream and the North Atlantic Subtropical High, modulating Southeast US rainfall
Eddy‐parameterizing CCSM4 and CMIP5 models may overestimate the role of tropical sea surface temperature in decadal Southeast US rainfall
