Mechanisms Controlling Global Mean Sea Surface Temperature Determined From a State Estimate

Abstract

AbstractGlobal mean sea surface temperature ( ) is a variable of primary interest in studies of climate variability and change. The temporal evolution of can be influenced by surface heat fluxes ( ) and by diffusion ( ) and advection ( ) processes internal to the ocean, but quantifying the contribution of these different factors from data alone is prone to substantial uncertainties. Here we derive a closed budget for the period 1993–2015 based on a global ocean state estimate, which is an exact solution of a general circulation model constrained to most extant ocean observations through advanced optimization methods. The estimated average temperature of the top (10‐m thick) level in the model, taken to represent , shows relatively small variability at most time scales compared to , , or , reflecting the tendency for largely balancing effects from all the latter terms. The seasonal cycle in is mostly determined by small imbalances between and , with negligible contributions from . While seems to simply damp at the annual period, a different dynamical role for at semiannual period is suggested by it being larger than . At periods longer than annual, contributes importantly to variability, pointing to the direct influence of the variable ocean circulation on and mean surface climate.