Evaluating modifications to air–sea momentum flux parameterizations under light wind conditions in CAM6

Parameterizing momentum flux under light wind conditions poses a challenge in the development of air-sea flux parameterizations. In this study, we evaluated some modifications to air–sea momentum flux parameterizations under light wind conditions, including surface layer effects (smooth flow and capillary waves), gustiness effects, and non-local effects. By coupling these modifications into the Community Atmosphere Model version 6 (CAM6), we conducted six sensitivity experiments to assess their direct impact on air–sea momentum flux under light wind conditions and their indirect impact on the simulation performance in low-latitude sea areas. During the iteration process in model, the complex negative feedback between wind speed and momentum flux led to differences in momentum flux patterns among experiments in the three key sea areas and inconsistency between offline and online test results. Based on the comprehensive evaluation metric Distance between Indices of Simulation and Observation (DISO), we assessed the simulation performance of experiments in the entire low-latitude sea area, the three key sea areas, and under light wind conditions. The discrepancy in the 10-m wind speeds deviation between light wind conditions and medium to strong wind conditions led to a reversal in the ranking of the simulation performance of the six experiments under light wind conditions compared to the entire low-latitude sea area.