Isolating the contribution of local and non-local shortwave flux biases towards climatological sea surface temperature and precipitation biases within a coupled climate model

Abstract

Coupled climate models suffer from persistent climatological biases in sea surface temperature (SST). The exact causes of these biases are often difficult to diagnose given the complex ocean-atmosphere interactions underpinning the seasonal cycle within these regions. Here, we investigate the possibility of reducing these biases within both low- and medium- resolution configurations of a fully-coupled climate model (CESM) by globally, and regionally, replacing the net shortwave (SW net ) flux at the surface with climatological values derived from Clouds and Earth's Radiant Energy Systems (CERES)-Energy Balanced And Filled (EBAF). This approach reduces the global mean SST bias. While the SST biases are reduced in several regions, such as the northern hemisphere subtropical gyres and the Pacific cold tongue, biases persist in some regions, notably the Southern Ocean. The persistence of these biases despite the shortwave forcing being correct points to shortcomings in other processes controlling the net surface heat flux, including the representation of surface mixed-layer processes in the ocean component. Additional regional replacement experiments highlight the contribution of both local and nonlocal biases in shortwave forcing towards SST biases.