Abstract
Abstract. A general circulation model of intermediate complexity with an idealized Earth-like aquaplanet setup is used to study the impact of changes in the oceanic heat transport on the global atmospheric circulation. Focus is on the atmospheric mean meridional circulation and global thermodynamic properties. The atmosphere counterbalances to a large extent the imposed changes in the oceanic heat transport, but, nonetheless, significant modifications to the atmospheric general circulation are found. Increasing the strength of the oceanic heat transport up to 2.5 PW leads to an increase in the global mean near-surface temperature and to a decrease in its equator-to-pole gradient. For stronger transports, the gradient is reduced further, but the global mean remains approximately constant. This is linked to a cooling and a reversal of the temperature gradient in the tropics. Additionally, a stronger oceanic heat transport leads to a decline in the intensity and a poleward shift of the maxima of both the Hadley and Ferrel cells. Changes in zonal mean diabatic heating and friction impact the properties of the Hadley cell, while the behavior of the Ferrel cell is mostly controlled by friction. The efficiency of the climate machine, the intensity of the Lorenz energy cycle and the material entropy production of the system decline with increased oceanic heat transport. This suggests that the climate system becomes less efficient and turns into a state of reduced entropy production as the enhanced oceanic transport performs a stronger large-scale mixing between geophysical fluids with different temperatures, thus reducing the available energy in the climate system and bringing it closer to a state of thermal equilibrium.
Highlights
The climate is a forced and dissipative nonequilibrium system, which – neglecting secular trends – can be considered to be in steady state, i.e., its statistical properties do not depend on time
Up to about OHTmax = 2.5 PW increasing oceanic heat transport (OHT) leads to an increase in the global mean (TM) and a decrease in the equator-to-pole gradient ( T ) of the annual and zonal mean www.earth-syst-dynam.net/6/591/2015/
For OHTmax > 2.5 PW, TM is almost insensitive to an OHT change, while T is further reduced with increasing intensity of transport
Summary
The climate is a forced and dissipative nonequilibrium system, which – neglecting secular trends – can be considered to be in steady state, i.e., its statistical properties do not depend on time. Stone concluded that features of the meridional heat transport can be related to the solar constant, the radius of the Earth, the tilt of the Earth’s axis and the hemispheric mean albedo He argued that the insensitivity to the structure and to the dynamics of the system is due to the correlation of thermal emissions to space, the albedo and the efficiency of the transport mechanisms of the atmosphere and the ocean. Enderton and Marshall concluded that Stone’s result is a good guide for ice-free climates They noted that the effect of the related meridional gradients in albedo on the absorption of solar radiation needs to be taken into account if polar ice caps are present. Appendices A–C give comprehensive descriptions of the main diagnostics
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