Sensitivity of Subsurface Ocean Temperature Variability to Specification of Surface Observations in the Context of ENSO

Abstract

Abstract To estimate the state of the ocean in the context of monitoring and prediction, ocean analysis products combine observed information from various sources that include both in situ ocean measurements and estimates of atmospheric forcings derived either from numerical models or from objective analysis methods. In the context of El Niño–Southern Oscillation (ENSO) variability in the equatorial tropical Pacific, this study discusses two questions: 1) the role of surface forcings in resolving the observed variability of subsurface ocean temperatures, and 2) which component of surface forcings plays a more important role. The analysis approach is based on ocean model simulations where specification of surface forcings is controlled and the resulting ocean state is either compared among various simulations or is compared with an independent ocean analysis (where information from in situ ocean temperature measurements is included). The results highlight the importance of the contribution of observed sea surface temperature (via its influence on surface winds due to coupled air–sea interactions) and the observed surface wind forcing in determining the evolution of subsurface ocean temperatures. Implications for assessing the feasibility of extending ocean analysis and forecasts back in time when in situ observations were limited are also discussed.