Tropical Pacific Air-Sea Interaction: Processes and Biases Relevant to ENSO and MJO

Oceanic and atmospheric variability in the eastern edge of Indo/western Pacific Warm Pool and associated oceanic subsurface features are essential for air-sea interactions involved in ENSO and MJO dynamics. In this study, we seek to determine the physical mechanisms governing air-sea interactions in the region, and thus the impacts of model biases under different timescales. We use the Ocean ReAnalysis System 5 (ORAS5) to identify mean-state biases in the NCAR Community Earth System Model version 2 (CESM2) with a particular focus on upper ocean properties and air-sea interaction processes, and show that the CESM2 has warm and fresh surface biases in the tropical Pacific Ocean, a barrier layer that is too thin in the western Pacific, and an isothermal layer depth that is too deep in the eastern Pacific, which impact air-sea interaction processes involved in ENSO onset. For shorter timescales, the MJO is responsible for weather variability in the tropics in the intraseasonal timescales. We analyze the subseasonal forecast from the European Centre for Medium-Range Weather Forecasts (ECMWF) with different initial ocean states to examine the influence of the subsurface ocean features on the development of biases through air-sea interaction processes. Based on these results, we emphasize how variability and model biases in barrier layer thickness and isothermal layer depth influence the air-sea interaction processes and therefore the evolution and prediction of ENSO and MJO in the tropical Pacific region.