scholarly journals Response of the Hadley Circulation to Climate Change in an Aquaplanet GCM Coupled to a Simple Representation of Ocean Heat Transport

2011 ◽  
Vol 68 (4) ◽  
pp. 769-783 ◽  
Author(s):  
Xavier J. Levine ◽  
Tapio Schneider
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Dynamical Regime ◽  
Ocean Heat Transport ◽  
Simple Representation ◽  
Wide Range ◽  
Momentum Fluxes

Abstract It is unclear how the width and strength of the Hadley circulation are controlled and how they respond to climate changes. Simulations of global warming scenarios with comprehensive climate models suggest the Hadley circulation may widen and weaken as the climate warms. But these changes are not quantitatively consistent among models, and how they come about is not understood. Here, a wide range of climates is simulated with an idealized moist general circulation model (GCM) coupled to a simple representation of ocean heat transport, in order to place past and possible future changes in the Hadley circulation into a broader context and to investigate the mechanisms responsible for them. By comparison of simulations with and without ocean heat transport, it is shown that it is essential to take low-latitude ocean heat transport and its coupling to wind stress into account to obtain Hadley circulations in a dynamical regime resembling Earth’s, particularly in climates resembling present-day Earth’s and colder. As the optical thickness of an idealized longwave absorber in the simulations is increased and the climate warms, the Hadley circulation strengthens in colder climates and weakens in warmer climates; it has maximum strength in a climate close to present-day Earth’s. In climates resembling present-day Earth’s and colder, the Hadley circulation strength is largely controlled by the divergence of angular momentum fluxes associated with eddies of midlatitude origin; the latter scale with the mean available potential energy in midlatitudes. The importance of these eddy momentum fluxes for the Hadley circulation strength gradually diminishes as the climate warms. The Hadley circulation generally widens as the climate warms, but at a modest rate that depends sensitively on how it is determined.

scholarly journals The Importance of Ocean Dynamical Feedback for Understanding the Impact of Mid–High-Latitude Warming on Tropical Precipitation Change

2018 ◽  
Vol 31 (6) ◽  
pp. 2417-2434 ◽  
Author(s):  
Masakazu Yoshimori ◽  
Ayako Abe-Ouchi ◽  
Hiroaki Tatebe ◽  
Toru Nozawa ◽  
Akira Oka
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Precipitation Change ◽  
Meridional Overturning Circulation ◽  
Climate Projections ◽  
Ocean Heat Transport ◽  
Tropical Precipitation ◽  
The Impact

It has been shown that asymmetric warming between the Northern and Southern Hemisphere extratropics induces a meridional displacement of tropical precipitation. This shift is believed to be due to the extra energy transported from the differentially heated hemisphere through changes in the Hadley circulation. Generally, the column-integrated energy flux in the mean meridional overturning circulation follows the direction of the upper, relatively dry branch, and tropical precipitation tends to be intensified in the hemisphere with greater warming. This framework was originally applied to simulations that did not include ocean dynamical feedback, but was recently extended to take the ocean heat transport change into account. In the current study, an atmosphere–ocean general circulation model applied with a regional nudging technique is used to investigate the impact of extratropical warming on tropical precipitation change under realistic future climate projections. It is shown that warming at latitudes poleward of 40° causes the northward displacement of tropical precipitation from October to January. Warming at latitudes poleward of 60° alone has a much smaller effect. This change in the tropical precipitation is largely explained by the atmospheric moisture transport caused by changes in the atmospheric circulation. The larger change in ocean heat transport near the equator, relative to the atmosphere, is consistent with the extended energy framework. The current study provides a complementary dynamical framework that highlights the importance of midlatitude atmospheric eddies and equatorial ocean upwelling, where the atmospheric eddy feedback modifies the Hadley circulation resulting in the northward migration of precipitation and the ocean dynamical feedback damps the northward migration from the equator.

scholarly journals The Response of Hadley Circulation Extent to an Idealized Representation of Poleward Ocean Heat Transport in an Aquaplanet GCM

2018 ◽  
Vol 31 (23) ◽  
pp. 9753-9770 ◽  
Author(s):  
Casey C. Hilgenbrink ◽  
Dennis L. Hartmann
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Static Stability ◽  
Vertical Shear ◽  
Ocean Heat Transport ◽  
Theoretical Understanding ◽  
Global Mean Temperature ◽  
Poleward Shift

Deeper theoretical understanding of Hadley circulation (HC) width and the mechanisms leading to HC expansion is gained by exploring the response of a zonally symmetric slab ocean aquaplanet general circulation model (GCM) to imposed poleward ocean heat transport (OHT). Poleward OHT causes the subtropical edge of the HC to shift poleward by up to 3° compared to its position in simulations without OHT. This HC widening is interpreted as being driven by a decrease in baroclinicity near the poleward edge of the HC and is divided into three components: a decrease in baroclinicity due to 1) a systematic poleward shift of the intertropical convergence zone (ITCZ) during the seasonal cycle that drives a decrease in the angular momentum of the HC and, consequently, a weakening of the vertical shear of the zonal wind; 2) an increase in subtropical static stability and the vertical extent of the HC, both of which result from OHT’s effect on global-mean temperature; and 3) a relaxation of the meridional sea surface temperature (SST) gradient in the outer tropics and subtropics by OHT. Although the third mechanism contributes the most to the response of HC width to OHT, the contributions from the first two mechanisms each account for up to 20%–30% of the HC response. This work highlights the role of ITCZ position in producing HC expansion and in setting the climatological width of the HC, a role which has been underappreciated. This study indicates a fundamental role for baroclinicity in limiting the poleward extent of the HC.

scholarly journals Effects of Tropical Cyclones on Ocean Heat Transport in a High-Resolution Coupled General Circulation Model

2011 ◽  
Vol 24 (16) ◽  
pp. 4368-4384 ◽  
Author(s):  
Enrico Scoccimarro ◽  
Silvio Gualdi ◽  
Alessio Bellucci ◽  
Antonella Sanna ◽  
Pier Giuseppe Fogli ◽  
...  
Keyword(s):  
Twentieth Century ◽  
High Resolution ◽  
Heat Transport ◽  
Tropical Cyclones ◽  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Ocean Heat Transport ◽  
Coupled General Circulation Model

Abstract In this paper the interplay between tropical cyclones (TCs) and the Northern Hemispheric ocean heat transport (OHT) is investigated. In particular, results from a numerical simulation of the twentieth-century and twenty-first-century climates, following the Intergovernmental Panel on Climate Change (IPCC) twentieth-century run (20C3M) and A1B scenario protocols, respectively, have been analyzed. The numerical simulations have been performed using a state-of-the-art global atmosphere–ocean–sea ice coupled general circulation model (CGCM) with relatively high-resolution (T159) in the atmosphere. The CGCM skill in reproducing a realistic TC climatology has been assessed by comparing the model results from the simulation of the twentieth century with available observations. The model simulates tropical cyclone–like vortices with many features similar to the observed TCs. Specifically, the simulated TCs exhibit realistic structure, geographical distribution, and interannual variability, indicating that the model is able to capture the basic mechanisms linking the TC activity with the large-scale circulation. The cooling of the surface ocean observed in correspondence of the TCs is well simulated by the model. TC activity is shown to significantly increase the poleward OHT out of the tropics and decrease the poleward OHT from the deep tropics on short time scales. This effect, investigated by looking at the 100 most intense Northern Hemisphere TCs, is strongly correlated with the TC-induced momentum flux at the ocean surface, where the winds associated with the TCs significantly weaken (strengthen) the trade winds in the 5°–18°N (18°–30°N) latitude belt. However, the induced perturbation does not impact the yearly averaged OHT. The frequency and intensity of the TCs appear to be substantially stationary through the entire 1950–2069 simulated period, as does the effect of the TCs on the OHT.

scholarly journals Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins

2012 ◽  
Vol 8 (4) ◽  
pp. 2445-2475 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Ice Cover ◽  
Ocean General Circulation Model ◽  
Snowball Earth ◽  
Ice Dynamics ◽  
Sea Ice Dynamics

Abstract. The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we revisit the initiation of a Snowball Earth in the atmosphere-ocean general circulation model ECHAM5/MPI-OM for Marinoan (~630 Ma) continents and solar insolation decreased to 94%. In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Previous work has shown that the Snowball Earth bifurcation can be pushed equatorward if a low bare sea ice albedo is assumed because bare sea ice is exposed by net evaporation in the descent region of the Hadley circulation. Consistent with this, when we replace the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a much lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, both lowering the bare sea-ice albedo and disabling sea-ice dynamics increase the critical sea-ice cover in ECHAM5/MPI-OM, but sea-ice dynamics have a much larger influence on the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no Jormungand bifurcation between this Jormungand-like state and states with mid-latitude sea-ice margins. Our results indicate that differences in sea-ice dynamics schemes can be as important as sea ice albedo for causing the spread in climate model's estimates of the location of the Snowball Earth bifurcation.

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.

scholarly journals Spatial climate models for Canada’s forestry community

2013 ◽  
Vol 89 (05) ◽  
pp. 659-663 ◽  
Author(s):  
Daniel McKenney ◽  
John Pedlar ◽  
Michael Hutchinson ◽  
Pia Papadopol ◽  
Kevin Lawrence ◽  
...  
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Smoothing Splines ◽  
The United States ◽  
Senior Author ◽  
Forest Community ◽  
Climate Projections ◽  
Normal Period ◽  
Wide Range

We summarize ongoing efforts at the Canadian Forest Service to produce spatial climate models for Canada and the United States. Our models, which encompass a wide range of variables and spatiotemporal extents, typically employ thin plate smoothing splines to interpolate and extrapolate climate station values as a function of latitude, longitude and elevation. The resulting surfaces can be resolved as grids (i.e., maps) or as point estimates at locations of interest. Recent efforts, detailed here include: updated models for the most recent 30-year normal period (i.e., 1981–2010), moisture balance models, future climate projections using the latest round of general circulation model (GCM) outputs and emissions scenarios, lake ice freeze/thaw models, and growing season models. These models are available to the Canadian forest community and beyond via the internet ( http://cfs.nrcan.gc.ca/projects/3 ) or by contacting the senior author.

Why Tropical Sea Surface Temperature is Insensitive to Ocean Heat Transport Changes

2013 ◽  
Vol 26 (18) ◽  
pp. 6742-6749 ◽  
Author(s):  
Daniel D. B. Koll ◽  
Dorian S. Abbot
Keyword(s):  
Heat Transport ◽  
Climate Models ◽  
Global Climate ◽  
Hadley Circulation ◽  
Global Climate Models ◽  
Sea Surface ◽  
Ocean Heat Transport ◽  
Additional Degree ◽  
Tropical Sea ◽  
Do So

AbstractPrevious studies have shown that increases in poleward ocean heat transport (OHT) do not strongly affect tropical SST. The goal of this paper is to explain this observation. To do so, the authors force two atmospheric global climate models (GCMs) in aquaplanet configuration with a variety of prescribed OHTs. It is found that increased OHT weakens the Hadley circulation, which decreases equatorial cloud cover and shortwave reflection, as well as reduces surface winds and evaporation, which both limit changes in tropical SST. The authors also modify one of the GCMs by alternatively setting the radiative effect of clouds to zero and disabling wind-driven evaporation changes to show that the cloud feedback is more important than the wind–evaporation feedback for maintaining constant equatorial SST as OHT changes. This work highlights the fact that OHT can reduce the meridional SST gradient without affecting tropical SST and could therefore serve as an additional degree of freedom for explaining past warm climates.

scholarly journals Climate Sensitivity to Changes in Ocean Heat Transport

2011 ◽  
Vol 24 (19) ◽  
pp. 5015-5030 ◽  
Author(s):  
Marcelo Barreiro ◽  
Annalisa Cherchi ◽  
Simona Masina
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Ocean Heat Transport ◽  
Sea Ice Extent ◽  
The Past ◽  
Low Clouds ◽  
Marine Stratus ◽  
Low Cloud

Using an atmospheric general circulation model coupled to a slab ocean, the effects of ocean heat transport (OHT) on climate are studied by prescribing OHT from 0 to 2 times the present-day values. In agreement with previous studies, an increase in OHT from zero to present-day conditions warms the climate by decreasing the albedo due to reduced sea ice extent and marine stratus cloud cover and by increasing the greenhouse effect through a moistening of the atmosphere. However, when the OHT is further increased, the solution becomes highly dependent on a positive radiative feedback between tropical low clouds and sea surface temperature. The strength of the low cloud–SST feedback combined with the model design may produce solutions that are globally colder than in the control run, mainly due to an unrealistically strong equatorial cooling. Excluding those cases, results indicate that the climate warms only if the OHT increase does not exceed more than 10% of the present-day value in the case of a strong cloud–SST feedback and more than 25% when this feedback is weak. Larger OHT increases lead to a cold state where low clouds cover most of the deep tropics, increasing the tropical albedo and drying the atmosphere. This suggests that the present-day climate is close to a state where the OHT maximizes its warming effects on climate and raises doubts about the possibility that greater OHT in the past may have induced significantly warmer climates than that of today.

scholarly journals Effects of Rotation Rate and Seasonal Forcing on the ITCZ Extent in Planetary Atmospheres

2017 ◽  
Vol 74 (3) ◽  
pp. 665-678 ◽  
Author(s):  
Sean Faulk ◽  
Jonathan Mitchell ◽  
Simona Bordoni
Keyword(s):  
Rotation Rate ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Earth’S Rotation ◽  
Quasi Equilibrium ◽  
Earth's Rotation ◽  
Weather Patterns ◽  
Rotation Rates ◽  
Wide Range

Abstract The authors study a wide range of atmospheric circulations with an idealized moist general circulation model to evaluate the mechanisms controlling intertropical convergence zone (ITCZ) migrations. They employ a zonally symmetric aquaplanet slab ocean of fixed depth and force top-of-atmosphere insolation to remain fixed at the pole for an “eternal solstice” simulation and also vary seasonally for a range of rotation rates, keeping all other parameters Earth-like. For rotation rates ΩE/8 and slower, a transient maximum in zonal-mean precipitation appears at the summer pole; however, the ITCZ associated with the ascending branch of the Hadley circulation lies at ~60°. The authors assess how widely used predictors of the ITCZ position perform in this wide parameter space. Standard predictors based on different estimates of the Hadley cell’s poleward extent are correlated with but overestimate off-equatorial ITCZ locations. Interestingly, in the eternal-solstice case for Earth’s rotation rate, the ITCZ remains at subtropical latitudes even though the lower-level moist static energy maximizes at the summer pole. While seemingly at odds with convective quasi-equilibrium arguments, this can happen because at Earth’s rotation rates, the thermal stratification set in convective regions can only be communicated within the tropics, where temperature gradients are constrained to be weak. The authors therefore develop an understanding of the ITCZ’s position based on top-of-atmosphere energetics and the boundary layer momentum budget and argue that friction and pressure gradient forces determine the region of maximum convergence, offering a modified dynamical perspective on the monsoon-like seasonal weather patterns of terrestrial planets.

Error Reduction and Convergence in Climate Prediction

2008 ◽  
Vol 21 (24) ◽  
pp. 6698-6709 ◽  
Author(s):  
Charles S. Jackson ◽  
Mrinal K. Sen ◽  
Gabriel Huerta ◽  
Yi Deng ◽  
Kenneth P. Bowman
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Model Development ◽  
Circulation Model ◽  
Extreme Rainfall ◽  
Optimization Process ◽  
Observational Uncertainty ◽  
Wide Range ◽  
Optimized Model

Abstract Although climate models have steadily improved their ability to reproduce the observed climate, over the years there has been little change to the wide range of sensitivities exhibited by different models to a doubling of atmospheric CO2 concentrations. Stochastic optimization is used to mimic how six independent climate model development efforts might use the same atmospheric general circulation model, set of observational constraints, and model skill criteria to choose different settings for parameters thought to be important sources of uncertainty related to clouds and convection. Each optimized model improved its skill with respect to observations selected as targets of model development. Of particular note were the improvements seen in reproducing observed extreme rainfall rates over the tropical Pacific, which was not specifically targeted during the optimization process. As compared to the default model sensitivity of 2.4°C, the ensemble of optimized model configurations had a larger and narrower range of sensitivities around 3°C but with different regional responses related to the uncertain choice in optimized parameter settings. These results suggest current generation models, if similarly optimized, may become more convergent in their measure of global sensitivity to greenhouse gas forcing. However, this exploration of the possible sources of modeling and observational uncertainty is not exhaustive. The optimization process illustrates an objective means for selecting an ensemble of plausible climate model configurations that quantify a portion of the uncertainty in the climate model development process.

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