| dc.description.abstract | Impact of model horizontal resolution on sea-surface temperature (SST) biases and ocean heat uptake (OHU) projections are studied by comparing high-resolution (HR) and low-resolution (LR) Community Earth System Model (CESM) multi-century simulations.
Results indicate that except over the eastern boundary upwelling systems SST is warmer in HR than LR. Globally averaged SST is 1oC warmer in HR than LR which is mainly attributed to stronger nonlocal vertical mixing and solar heat flux. The impact of nonlocal vertical mixing prevails over solar heat flux in eddy-active regions. In the tropics, nonlocal vertical mixing and solar heat flux contribute equally to the warmer SST in HR. The stronger nonlocal mixing in HR can be attributed to both the surface heat flux and shape function used in the nonlocal vertical mixing parameterization, and these two show a nonlinear relationship. The stronger solar heat flux in HR is mainly caused by less clouds in the tropics. The improved western boundary currents in HR also contribute to the reduction of SST biases in eddy-active regions.
The full-depth integrated OHU in HR and LR show small differences while vertical distributions of OHU are different. HR shows larger OHU in the upper 250 m than LR, but weaker OHU below 250 m. This difference is largely blamed to the difference in the eddy induced vertical heat transport (EVHT) between HR and LR. Moreover, the parameterized EVHT in LR is found to be more sensitive to the ocean stratification changes than the resolved EVHT in HR. The stronger OHU in the upper 250 m in HR is found to be distributed to the north of 35oS (NR). To the south of 35oS, OHU in HR is less than LR from the surface to seafloor which is attributed to the difference in the mean-flow induced meridional heat transport (MMHT) changes across 35oS in the Indian Ocean. Compared with the difference in gyre circulation changes between HR and LR, the difference in the meridional overturning circulation changes shows a dominant contribution to the difference in MMHT changes in the Indian Ocean. In the upper 250 m, the Arctic can explain 26.32% of OHU difference in NR between HR and LR although the volume only accounts for 4% of that of NR. The difference in Arctic OHU is caused by the difference of MHT changes across 65oN between HR and LR.
Overall, this study sheds new light on how resolved ocean eddy processes in HR and parameterized eddy processes in LR contribute differently to modeling SST and OHU. These new results can have important implications to improve simulations and projections of future climate change. | |
