A New Hybrid Coupled Model of Atmosphere, Ocean Physics, and Ocean Biogeochemistry to Represent Biogeophysical Feedback Effects in the Tropical Pacific

Multiple processes are involved in modulating the El Nino-Southern Oscillation (ENSO) in the tropical Pacific, and these processes are neither well-represented nor well-understood in climate models. A new hybrid coupled model (HCM) of atmosphere, ocean physics, and ocean biogeochemistry (AOPB) is developed to represent the feedback from ocean biogeochemistry onto ocean physics via modulating the penetration of shortwave radiation in the upper ocean. An ocean biogeochemistry model is coupled with a simplified ocean-atmosphere system consisting of an ocean general circulation model (OGCM) and a statistical atmospheric model for interannual anomalies of wind stress (tau). The HCM AOPB serves as a simple Earth system for the tropical Pacific to represent the coupling among the atmospheric and physical and biogeochemical ocean components. Model experiments are performed to illustrate this new model's ability to depict the mean ocean state and interannual variability associated with the ENSO. The relationships among anomaly fields are analyzed to illustrate the ocean biogeochemistry-induced heating feedback and its modulating effects on the ENSO, which is characterized by a negative feedback. The underlying processes and mechanisms are analyzed and can be attributed to dominant modulation of the penetrative solar radiation through the base of the mixed layer (ML). It is demonstrated that the ocean biogeochemistry-induced negative feedback is mainly driven by more solar radiation penetrating out of the ML during El Nino and less penetrating during La Nina. Further model applications to studies on these processes and biogeochemical-physical interactions are discussed.