Jeffery R. Scott

Tropical Cyclone–Induced Upper-Ocean Mixing and Climate: Application to Equable Climates

Abstract Tropical cyclones instigate an isolated blast of vigorous mixing in the upper tropical oceans, stirring warm surface water with cooler water in the thermocline. Previous work suggests that the frequency, intensity, and lifetime of these storms may be functions of the climate state, implying that transient tropical mixing could have been stronger during warmer equable climates with higher concentrations of carbon dioxide. Stronger mixing of the tropical oceans can force the oceans’ meridional heat flux to increase, cooling tropical latitudes while warming higher ones. This response differs significantly from previous modeling studies of equable climates that used static mixing; coupling mixing to climate changes the dynamic response. A parameterization of mixing from tropical cyclones is developed, and including it leads to a cooling of tropical oceans and a warming of subtropical waters compared with control cases with fixed mixing. The mixing penetration depth regulates the magnitude of the resp...

Convective Mixing and the Thermohaline Circulation

Abstract An idealized three-dimensional model of buoyancy-driven flow in a single hemisphere is used to investigate the relationship between the meridional overturning and the efficiency by which convective mixing eliminates static instability. In the “fast” limit (mixing timescale hours to weeks), the meridional overturning is not rate limited by the efficiency of convective mixing. If convective mixing is made less efficient, the model’s meridional overturning strength increases. Moreover, the dominant downwelling occurs not at the highest surface density;hence the deep ocean is relatively buoyant. The numerical results are explained by the different influences of convective mixing and downward advection on the deep-ocean heat budget; they underscore the fundamentally three-dimensional nature of the meridional overturning. In addition, the narrowness of deep downwelling is related to the geostrophic dynamics of deep temperature anomalies near the eastern wall. The model results presented here are in con...

Impact of geothermal heating on the global ocean circulation

The response of a global circulation model to a uniform geothermal heat flux of 50 mW m 2 through the sea floor is examined. If the geothermal heat input weretransportedupwardpurelybydiusion,thedeepocean wouldwarmby1.2C.However,geothermalheatinginduces a substantial change in the deep circulation which is larger than previously assumed and subsequently the warming of the deep ocean is only a quarter of that suggested by the diusive limit. The numerical ocean model responds most strongly in the Indo-Pacic with an increase in meridional overturningof1.8 Sv,enhancingtheexistingoverturningby approximately 25%.

The Location of Diapycnal Mixing and the Meridional Overturning Circulation

Abstract The large-scale consequences of diapycnal mixing location are explored using an idealized three-dimensional model of buoyancy-forced flow in a single hemisphere. Diapycnal mixing is most effective in supporting a strong meridional overturning circulation (MOC) if mixing occurs in regions of strong stratification, that is, in the low-latitude thermocline where diffusion causes strong vertical buoyancy fluxes. Where stratification is weak, such as at high latitudes, diapycnal mixing plays little role in determining MOC strength, consistent with weak diffusive buoyancy fluxes at these latitudes. Boundary mixing is more efficient than interior mixing at driving the MOC; with interior mixing the planetary vorticity constraint inhibits the communication of interior water mass properties and the eastern boundary. Mixing below the thermocline affects the abyssal stratification and upwelling profile but does not contribute significantly to the meridional flow through the thermocline or the oceans meridio...

The ocean’s role in the transient response of climate to abrupt greenhouse gas forcing

We study the role of the ocean in setting the patterns and timescale of the transient response of the climate to anthropogenic greenhouse gas forcing. A novel framework is set out which involves integration of an ocean-only model in which the anthropogenic temperature signal is forced from the surface by anomalous downwelling heat fluxes and damped at a rate controlled by a ‘climate feedback’ parameter. We observe a broad correspondence between the evolution of the anthropogenic temperature (

The ocean's role in polar climate change: asymmetric Arctic and Antarctic responses to greenhouse gas and ozone forcing*

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Valuing climate impacts in integrated assessment models: the MIT IGSM

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