scholarly journals Exploring the Climatic Response to Wide Variations in Ocean Heat Transport on an Aquaplanet

2018 ◽  
Vol 31 (16) ◽  
pp. 6299-6318 ◽  
Author(s):  
M. Cameron Rencurrel ◽  
Brian E. J. Rose
Keyword(s):  
Heat Transport ◽  
Climate Model ◽  
Hadley Circulation ◽  
Balance Model ◽  
Ocean Heat Transport ◽  
Climatic Impact ◽  
Ocean Heat Uptake ◽  
Boundary Layer Clouds ◽  
Radiative Processes ◽  
The Tropics

The climatic impact of ocean heat transport (OHT) is studied in a series of idealized aquaplanet climate model experiments. OHT is prescribed through a simple geometrical formula spanning a wide variety of amplitudes and meridional extents. Calculations with a comprehensive GCM are compared against a simple diffusive energy balance model (EBM). The GCM response differs from the EBM in several important ways that illustrate linkages between atmospheric dynamics and radiative processes. Increased OHT produces global mean warming at a rate of 2 K PW−1 OHT across 30° and a strong reduction in meridional temperature gradient. The tropics remain nearly isothermal despite locally large imposed ocean heat uptake. The warmer climate features reduced equatorial convection, moister subtropics, reduced cloudiness, and partial but incomplete compensation in atmospheric heat transport. Many of these effects are linked to a weakened Hadley circulation. Both the warming pattern and hydrological changes differ strongly from those driven by CO2. Similar results are found at 0° and 23.45° obliquity. It is argued that clouds, rather than clear-sky radiative processes, are principally responsible for the global warming and tropical thermostat effects. Cloud changes produce warming in all cases, but the degree of warming depends strongly on the meridional extent of OHT. The strongest warming occurs in response to mid- to high-latitude OHT convergence, which produces widespread loss of boundary layer clouds. Temperature responses to increased OHT are quantitatively reproduced in the EBM by imposing GCM-derived cloud radiative effects as additional forcing.

scholarly journals Ocean Heat Transport and Water Vapor Greenhouse in a Warm Equable Climate: A New Look at the Low Gradient Paradox

2012 ◽  
Vol 26 (6) ◽  
pp. 2117-2136 ◽  
Author(s):  
Brian E. J. Rose ◽  
David Ferreira
Keyword(s):  
Heat Transport ◽  
Large Scale ◽  
Energy Transport ◽  
Deep Convection ◽  
Analytical Formula ◽  
Storm Tracks ◽  
Convective Precipitation ◽  
Ocean Heat Transport ◽  
Climatic Impact ◽  
The Tropics

Abstract The authors study the role of ocean heat transport (OHT) in the maintenance of a warm, equable, ice-free climate. An ensemble of idealized aquaplanet GCM calculations is used to assess the equilibrium sensitivity of global mean surface temperature and its equator-to-pole gradient (ΔT) to variations in OHT, prescribed through a simple analytical formula representing export out of the tropics and poleward convergence. Low-latitude OHT warms the mid- to high latitudes without cooling the tropics; increases by 1°C and ΔT decreases by 2.6°C for every 0.5-PW increase in OHT across 30° latitude. This warming is relatively insensitive to the detailed meridional structure of OHT. It occurs in spite of near-perfect atmospheric compensation of large imposed variations in OHT: the total poleward heat transport is nearly fixed. The warming results from a convective adjustment of the extratropical troposphere. Increased OHT drives a shift from large-scale to convective precipitation in the midlatitude storm tracks. Warming arises primarily from enhanced greenhouse trapping associated with convective moistening of the upper troposphere. Warming extends to the poles by atmospheric processes even in the absence of high-latitude OHT. A new conceptual model for equable climates is proposed, in which OHT plays a key role by driving enhanced deep convection in the midlatitude storm tracks. In this view, the climatic impact of OHT depends on its effects on the greenhouse properties of the atmosphere, rather than its ability to increase the total poleward energy transport.

The Role of the Ocean in the Seasonal Cycle of the Hadley Circulation

2006 ◽  
Vol 63 (12) ◽  
pp. 3351-3365 ◽  
Author(s):  
Amy C. Clement
Keyword(s):  
Heat Transport ◽  
Seasonal Cycle ◽  
Climate Model ◽  
Hadley Circulation ◽  
Ocean Heat Transport ◽  
Complete Understanding ◽  
Atmospheric Processes ◽  
Summer Hemisphere ◽  
Hadley Cells

The influence of ocean heat transport on the seasonal cycle of the Hadley circulation is investigated using idealized experiments with a climate model. It is found that ocean heat transport plays a fundamental role in setting the structure and intensity of the seasonal Hadley cells. The ocean’s influence can be understood primarily via annual mean considerations. By cooling the equatorial regions and warming the subtropics in a year-round sense, the ocean heat transport allows for regions of SST maxima to occur off the equator in the summer hemisphere. This leads to large meridional excursions of convection over the ocean and a seasonal Hadley circulation that is strongly asymmetric about the equator. The broadening of the latitudinal extent of the SST maximum and the convecting regions by the ocean heat transport also weakens the annual mean Hadley circulation in a manner that is consistent with simpler models. The results are discussed in the context of prior studies of the controls on the strength and structure of the Hadley circulation. It is suggested that a complete understanding of the seasonal Hadley circulation must include both oceanic and atmospheric processes and their interactions.

Large ensemble assessment of how the global surface warming response to cumulative carbon differs for negative and positive carbon emissions  

2021 ◽  
Author(s):  
Negar Vakilifard ◽  
Katherine Turner ◽  
Ric Williams ◽  
Philip Holden ◽  
Neil Edwards ◽  
...  
Keyword(s):  
Carbon Emissions ◽  
Radiative Forcing ◽  
Climate Model ◽  
Climate Feedback ◽  
Climate Response ◽  
Ocean Heat Uptake ◽  
Transient Climate Response ◽  
Surface Warming ◽  
Radiative Processes ◽  
Negative Emission

<p>The controls of the effective transient climate response (TCRE), defined in terms of the dependence of surface warming since the pre-industrial to the cumulative carbon emission, is explained in terms of climate model experiments for a scenario including positive emissions and then negative emission over a period of 400 years. We employ a pre-calibrated ensemble of GENIE, grid-enabled integrated Earth system model, consisting of 86 members to determine the process of controlling TCRE in both CO<sub>2</sub> emissions and drawdown phases. Our results are based on the GENIE simulations with historical forcing from AD 850 including land use change, and the future forcing defined by CO<sub>2</sub> emissions and a non-CO<sub>2</sub> radiative forcing timeseries. We present the results for the point-source carbon capture and storage (CCS) scenario as a negative emission scenario, following the medium representative concentration pathway (RCP4.5), assuming that the rate of emission drawdown is 2 PgC/yr CO<sub>2</sub> for the duration of 100 years. The climate response differs between the periods of positive and negative carbon emissions with a greater ensemble spread during the negative carbon emissions. The controls of the spread in ensemble responses are explained in terms of a combination of thermal processes (involving ocean heat uptake and physical climate feedback), radiative processes (saturation in radiative forcing from CO<sub>2</sub> and non-CO<sub>2</sub> contributions) and carbon dependences (involving terrestrial and ocean carbon uptake).  </p>

scholarly journals Southern Ocean Heat Uptake, Redistribution, and Storage in a Warming Climate: The Role of Meridional Overturning Circulation

2018 ◽  
Vol 31 (12) ◽  
pp. 4727-4743 ◽  
Author(s):  
Wei Liu ◽  
Jian Lu ◽  
Shang-Ping Xie ◽  
Alexey Fedorov
Keyword(s):  
Southern Ocean ◽  
Heat Transport ◽  
Climate Models ◽  
Climate Model ◽  
Meridional Overturning Circulation ◽  
The Other ◽  
Anthropogenic Heat ◽  
Overturning Circulation ◽  
Ocean Heat Uptake ◽  
Meridional Overturning

Climate models show that most of the anthropogenic heat resulting from increased atmospheric CO2 enters the Southern Ocean near 60°S and is stored around 45°S. This heat is transported to the ocean interior by the meridional overturning circulation (MOC) with wind changes playing an important role in the process. To isolate and quantify the latter effect, we apply an overriding technique to a climate model and decompose the total ocean response to CO2 increase into two major components: one due to wind changes and the other due to direct CO2 effect. We find that the poleward-intensified zonal surface winds tend to shift and strengthen the ocean Deacon cell and hence the residual MOC, leading to anomalous divergence of ocean meridional heat transport around 60°S coupled to a surface heat flux increase. In contrast, at 45°S we see anomalous convergence of ocean heat transport and heat loss at the surface. As a result, the wind-induced ocean heat storage (OHS) peaks at 46°S at a rate of 0.07 ZJ yr−1 (° lat)−1 (1 ZJ = 1021 J), contributing 20% to the total OHS maximum. The direct CO2 effect, on the other hand, very slightly alters the residual MOC but primarily warms the ocean. It induces a small but nonnegligible change in eddy heat transport and causes OHS to peak at 42°S at a rate of 0.30 ZJ yr−1 (° lat)−1, accounting for 80% of the OHS maximum. We also find that the eddy-induced MOC weakens, primarily caused by a buoyancy flux change as a result of the direct CO2 effect, and does not compensate the intensified Deacon cell.

Examination of Isentropic Circulation Response to a Doubling of Carbon Dioxide Using Statistical Transformed Eulerian Mean*

2013 ◽  
Vol 70 (6) ◽  
pp. 1649-1667 ◽  
Author(s):  
Yutian Wu ◽  
Olivier Pauluis
Keyword(s):  
Heat Transport ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Isentropic Flow ◽  
Warming World ◽  
The Tropics ◽  
Transformed Eulerian Mean

Abstract Responses of the atmospheric circulation to a doubling of CO2 are examined in a global climate model, focusing on the circulation on both dry and moist isentropes. The isentropic circulations are reconstructed using the statistical transformed Eulerian mean (STEM), which approximates the isentropic flow from the Eulerian-mean and second-order moments. This approach also makes it possible to decompose the changes in the circulation into changes in zonal mean and eddy statistics. It is found that, as a consequence of CO2 doubling, the dry isentropic circulation weakens across all latitudes. The weaker circulation in the tropics is a result of the reduction in mean meridional circulation while the reduction in eddy sensible heat flux largely contributes to the slowdown of the circulation in the midlatitudes. The heat transport on dry isentropes, however, increases in the tropics because of the increase in dry effective stratification whereas it decreases in the extratropics following the reduction in eddy sensible heat transport. Distinct features are found on moist isentropes. In the tropics, the circulation weakens, but without much change in heat transport. The extratropical circulation shifts poleward with an intensification (weakening) on the poleward (equatorward) flank, primarily because of the change in eddy latent heat transport. The total heat transport in the midlatitudes also shows a poleward shift but is of smaller magnitude. The differences between the dry and moist circulations reveal that in a warming world the increase in midlatitude eddy moisture transport is associated with an increase in warm moist air exported from the subtropics into the midlatitude storm tracks.

scholarly journals Climate Determinism Revisited: Multiple Equilibria in a Complex Climate Model

2011 ◽  
Vol 24 (4) ◽  
pp. 992-1012 ◽  
Author(s):  
David Ferreira ◽  
John Marshall ◽  
Brian Rose
Keyword(s):  
Energy Balance ◽  
Sea Ice ◽  
Heat Transport ◽  
Ocean Circulation ◽  
General Circulation ◽  
Multiple Equilibria ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Ocean Heat Transport ◽  
Ice Cap

Abstract Multiple equilibria in a coupled ocean–atmosphere–sea ice general circulation model (GCM) of an aquaplanet with many degrees of freedom are studied. Three different stable states are found for exactly the same set of parameters and external forcings: a cold state in which a polar sea ice cap extends into the midlatitudes; a warm state, which is ice free; and a completely sea ice–covered “snowball” state. Although low-order energy balance models of the climate are known to exhibit intransitivity (i.e., more than one climate state for a given set of governing equations), the results reported here are the first to demonstrate that this is a property of a complex coupled climate model with a consistent set of equations representing the 3D dynamics of the ocean and atmosphere. The coupled model notably includes atmospheric synoptic systems, large-scale circulation of the ocean, a fully active hydrological cycle, sea ice, and a seasonal cycle. There are no flux adjustments, with the system being solely forced by incoming solar radiation at the top of the atmosphere. It is demonstrated that the multiple equilibria owe their existence to the presence of meridional structure in ocean heat transport: namely, a large heat transport out of the tropics and a relatively weak high-latitude transport. The associated large midlatitude convergence of ocean heat transport leads to a preferred latitude at which the sea ice edge can rest. The mechanism operates in two very different ocean circulation regimes, suggesting that the stabilization of the large ice cap could be a robust feature of the climate system. Finally, the role of ocean heat convergence in permitting multiple equilibria is further explored in simpler models: an atmospheric GCM coupled to a slab mixed layer ocean and an energy balance model.

Implied ocean heat transport in CMIP6 models

2021 ◽  
Author(s):  
Francesca Pearce ◽  
Alejandro Bodas-Salcedo ◽  
Christopher Thomas ◽  
Thomas Allen
Keyword(s):  
Heat Transport ◽  
Energy Budget ◽  
Climate Models ◽  
Surface Fluxes ◽  
Radiative Energy ◽  
Ocean Heat Transport ◽  
Energy Fluxes ◽  
Data Set ◽  
Ocean Heat Uptake ◽  
Energy Convergence

<p>The importance of heat transport in the ocean to maintain energy balance between different regions is well known, with heat typically being transported from the Equator to high latitudes. Ocean heat transport (OHT) can be separated into two different components; a divergent component which contributes directly to the Earths’ energy budget as it is the energy that converges in an ocean basin to balance the release of heat into the atmosphere, and a rotational component which does not affect the energy budget. Climate models show significant uncertainty in projections of ocean heat uptake, both in terms of the magnitude and geographical pattern. Since the oceans’ response under climate changes depends on the patterns of surface energy fluxes, it is important to assess the simulation of surface fluxes as a potential constraint of transient and long-term responses of the Earths’ climate. Assuming that the ocean absorbs all of the excess energy within the Earth system, it is possible to directly relate the net surface flux (NSF) over the ocean to divergent OHT, potentially providing a metric to quantify how well climate models are able to reproduce observed patterns of NSF and OHT. In this work, we present a detailed comparison of different methods used to calculate divergent OHT from the NSF over the ocean using data from various CMIP6 models. The methods investigated include a least-squares solution to a matrix equation in which energy convergence is related to NSF via the Earths’ energy imbalance, and solving a Poisson equation over the ocean surface (see Forget and Ferreira 2020). Comparison to observational estimates of OHT requires that the observational data set includes only sources of divergent heat transport, which is often not the case. Therefore, we intend to produce a data set of radiative energy fluxes that are consistent with both energy and water constraints (see Rodell et al. 2015, L’Ecuyer et al. 2015, Thomas et al. 2020) which can be subject to the same methods of determining OHT, and see how these estimates compare to the results from climate models.</p>

scholarly journals Relations between Northward Ocean and Atmosphere Energy Transports in a Coupled Climate Model

2008 ◽  
Vol 21 (3) ◽  
pp. 561-575 ◽  
Author(s):  
Michael Vellinga ◽  
Peili Wu
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Energy Transport ◽  
Climate Model ◽  
Atmospheric Transport ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Ocean Heat Transport ◽  
Poleward Heat Transport ◽  
Low Latitudes

Abstract The Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) is used to analyze the relation between northward energy transports in the ocean and atmosphere at centennial time scales. In a transient water-hosing experiment, where suppressing the Atlantic meridional overturning circulation (MOC) causes a reduction in northward ocean heat transport of up to 0.75 PW (i.e., 75%), the atmosphere compensates by increasing its northward transport of moist static energy. This compensation is very efficient at low latitudes and near complete at the equator throughout the experiment, but is incomplete farther north across the northern midlatitude storm tracks. The change in atmosphere energy transport enables the model to find a new global-mean radiative equilibrium after 240 yr. In a perturbed physics ensemble of HadCM3 it was found that time-averaged meridional energy transports in ocean and atmosphere can act opposingly. Where model formulation causes an unbalanced mean climate state, for example, an excessive top-of-the-atmosphere radiative surplus at low latitudes, the atmosphere increases its poleward energy transport to disperse this excess. MOC and ocean poleward heat transport tend to be reduced in such model versions, and this offsets the increased poleward atmospheric transport of the low-latitude energy surplus. Model versions that are close to net radiative equilibrium also have ocean heat transport and MOC close to observed values.

Interactions between ocean heat transport and Arctic sea ice

2020 ◽  
Author(s):  
David Docquier ◽  
Ramon Fuentes-Franco ◽  
Klaus Wyser ◽  
Torben Koenigk
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Arctic Sea Ice ◽  
Ocean Heat Transport ◽  
Arctic Sea ◽  
Fast Pace ◽  
Area And Volume

<p>Arctic sea ice has been retreating at fast pace in the last decades, with potential impacts on the weather and climate at mid and high latitudes, as well as the biosphere and society. Sea-ice loss is driven by anthropogenic global warming, atmospheric circulation changes, climate feedbacks, and ocean heat transport. To date, no clear consensus regarding the detailed impact of ocean heat transport on Arctic sea ice exists. Previous observational and modeling studies show that the poleward Atlantic Ocean heat transport and Arctic sea-ice area and volume are generally anti-correlated, suggesting a decrease in sea-ice area and volume with larger ocean heat transport. In turn, the changing sea ice may also affect ocean heat transport, but this effect has been much less studied. Our study explores the two-way interactions between ocean heat transport and Arctic sea ice. We use the EC-Earth global climate model, coupling the atmosphere and ocean, and perform different sensitivity experiments to gain insights into these interactions. The mechanisms by which ocean heat transport and Arctic sea ice interact are analyzed, and compared to observations. This study provides a way to better constrain model projections of Arctic sea ice, based on the relationships between ocean heat transport and Arctic sea ice.</p>

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