Abstract
AbstractThe classic vertical advection‐diffusion (VAD) balance is a central concept in studying the ocean heat budget, in particular in simple climate models (SCMs). Here we present a new framework to calibrate the parameters of the VAD equation to the vertical ocean heat balance of two fully‐coupled climate models that is traceable to the models' circulation as well as to vertical mixing and diffusion processes. Based on temperature diagnostics, we derive an effective vertical velocity w∗ and turbulent diffusivity for each individual physical process. In steady state, we find that the residual vertical velocity and diffusivity change sign in middepth, highlighting the different regional contributions of isopycnal and diapycnal diffusion in balancing the models' residual advection and vertical mixing. We quantify the impacts of the time evolution of the effective quantities under a transient 1% CO2 simulation and make the link to the parameters of currently employed SCMs.
Highlights
The vertical ocean heat balance plays a fundamental part in the Earth’s energy balance, where the latter describes the partitioning of additional radiative forcing in the climate system into ocean heat uptake and a temperature response [e.g., Gregory and Forster, 2008; Knutti and Hegerl, 2008; Church et al, 2011; Huber and Knutti, 2011]
Using temperature tendencies of individual physical processes that set the ocean heat balance of two coupled climate models, we introduce a new framework to relate the vertical heat budget to the classic upwelling-diffusion balance of Munk [1966], which is the basis of many simple climate models
The framework presented here takes into account that the horizontally averaged ocean heat balance is dominated by the extratropics [e.g., Exarchou et al, 2014], a region which is treated in simple climate models (SCMs) mostly implicitly
Summary
The vertical ocean heat balance plays a fundamental part in the Earth’s energy balance, where the latter describes the partitioning of additional radiative forcing in the climate system into ocean heat uptake and a temperature response [e.g., Gregory and Forster, 2008; Knutti and Hegerl, 2008; Church et al, 2011; Huber and Knutti, 2011]. Munk and Wunsch [1998], where the latter study considered a depth-dependent kν Such a model regards the vertical heat balance as a competition between the cooling effect due to the upwelling of cold abyssal waters induced by high-latitude deep water formation on the one hand and the downward diffusion of heat on the other hand. Based on the temperature diagnostics of an eddy-parameterizing and an eddy-permitting climate model, we present a new framework for achieving a physical calibration of w and kν by linking the two parameters to the actual physical processes of the models, resulting in an effective vertical velocity w∗ and an effective turbulent diffusivity kν∗ for each advective, diffusive, and mixing process Such temperature diagnostics have been analyzed previously in the context of idealized transient and abrupt climate change scenarios [e.g., Gregory, 2000; Exarchou et al, 2014]. We further present the time evolution of the effective quantities under an idealized transient climate change simulation and demonstrate that these spatial and time variations are key to evaluating the transient ocean heat uptake
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