The Response of Large-Scale Circulation to Obliquity-Induced Changes in Meridional Heating Gradients

2014 ◽  
Vol 27 (14) ◽  
pp. 5504-5516 ◽  
Author(s):  
Damianos F. Mantsis ◽  
Benjamin R. Lintner ◽  
Anthony J. Broccoli ◽  
Michael P. Erb ◽  
Amy C. Clement ◽  
...  
Keyword(s):  
Heat Transport ◽  
Large Scale ◽  
Climate Model ◽  
Hadley Circulation ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Hadley Cell ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Summer Hemisphere ◽  
Insolation Change

Abstract The inter- and intrahemispheric climate responses to a change in obliquity are investigated using the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1. (GFDL CM2.1). Reduced obliquity causes a weakening of the seasonal insolation contrast between the summer and winter hemispheres and a strengthening of the meridional insolation gradient within the summer hemisphere. The interhemispheric insolation change is associated with weakening of the cross-equatorial Hadley circulation and reduced heat transport from the summer hemisphere to the winter hemisphere, in both the ocean and atmosphere. In contrast, the intrahemispheric insolation change is associated with increased midlatitude summer eddy activity as seen by the increased atmospheric heat transport at those latitudes. Analysis of the zonal mean atmospheric meridional overturning circulation on isentropic surfaces confirms the increase of the midlatitude eddy circulation, which is driven by changes of sensible and latent heat fluxes, as well as changes in the stratification or distribution of entropy. It is suggested that the strengthening of this circulation is associated with an equatorward shift of the ascending branch of the winter Hadley cell.

scholarly journals MEP solution for a minimal climate model: success and limitation of a variational problem

2011 ◽  
Vol 2 (1) ◽  
pp. 393-434
Author(s):  
S. Pascale ◽  
J. M. Gregory ◽  
M. H. P. Ambaum ◽  
R. Tailleux ◽  
V. Lucarini
Keyword(s):  
Entropy Production ◽  
Heat Transport ◽  
Large Scale ◽  
Climate Model ◽  
Longwave Radiation ◽  
Critical Discussion ◽  
Heat Fluxes ◽  
Box Model ◽  
Temperature Fields ◽  
Vertical Heat

Abstract. Maximum Entropy Production conjecture (MEP) is applied to a minimal four-box model of climate which accounts for both horizontal and vertical material heat fluxes. It is shown that, under condition of fixed insolation, a MEP solution is found with reasonably realistic temperature and heat fluxes, thus generalising results from independent two-box horizontal or vertical models. It is also shown that the meridional and the vertical entropy production terms are independently involved in the maximisation and thus MEP can be applied to each subsystem with fixed boundary conditions. We then extend the four-box model by increasing its number of degrees of freedom, and test its realism by comparing it with a GCM output. An order-of-magnitude evaluation of contributions to the material entropy production (≈50 mW m−2 K−1) due to horizontal and vertical processes within the climate system is carried out by using ad hoc temperature fields. It turns out that approximately 40 mW m−2 K−1 is the entropy production due to vertical heat transport and 5–7 mW m−2 K−1 to horizontal heat transport. A MEP solution is found which is fairly realistic as far as the horizontal large scale organisation of the surface climate is concerned whereas the vertical structure looks to be unrealistic and presents seriously unstable features. Finally a more general problem is investigated in which the longwave transmissivity is varied simultaneously with the temperature. This leads to a MEP solution characterised by a much warmer climate, with very vigorous vertical heat fluxes, in which the atmosphere is opaque to longwave radiation. A critical discussion about how to interpret MEP and how to apply it in a physically correct way concludes the paper.

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.

scholarly journals The Hadley Circulation in Reanalyses: Climatology, Variability, and Change

2013 ◽  
Vol 26 (10) ◽  
pp. 3357-3376 ◽  
Author(s):  
H. Nguyen ◽  
A. Evans ◽  
C. Lucas ◽  
I. Smith ◽  
B. Timbal
Keyword(s):  
Large Scale ◽  
Southern Oscillation ◽  
Average Rate ◽  
Hadley Circulation ◽  
Hadley Cell ◽  
Momentum Balance ◽  
Annular Modes ◽  
Modes Of Variability ◽  
Summer Hemisphere ◽  
High Phase

Abstract Analysis of the annual cycle of intensity, extent, and width of the Hadley circulation across a 31-yr period (1979–2009) from all existent reanalyses reveals a good agreement among the datasets. All datasets show that intensity is at a maximum in the winter hemisphere and at a minimum in the summer hemisphere. Maximum and minimum values of meridional extent are reached in the respective autumn and spring hemispheres. While considering the horizontal momentum balance, where a weakening of the Hadley cell (HC) is expected in association with a widening, it is shown here that there is no direct relationship between intensity and extent on a monthly time scale. All reanalyses show an expansion in both hemispheres, most pronounced and statistically significant during summer and autumn at an average rate of expansion of 0.55° decade−1 in each hemisphere. In contrast, intensity trends are inconsistent among the datasets, although there is a tendency toward intensification, particularly in winter and spring. Correlations between the HC and tropical and extratropical large-scale modes of variability suggest interactions where the extent of the HC is influenced by El Niño–Southern Oscillation (ENSO) and the annular modes. The cells tend to shrink (expand) during the warm (cold) phase of ENSO and during the low (high) phase of the annular modes. Intensity appears to be influenced only by ENSO and only during spring for the southern cell and during winter for the northern cell.

scholarly journals Oceanic Overturning and Heat Transport: The Role of Background Diffusivity

2019 ◽  
Vol 32 (3) ◽  
pp. 701-716 ◽  
Author(s):  
Magnus Hieronymus ◽  
Jonas Nycander ◽  
Johan Nilsson ◽  
Kristofer Döös ◽  
Robert Hallberg
Keyword(s):  
Heat Transport ◽  
Large Scale ◽  
Energy Transport ◽  
Climate Model ◽  
Potential Temperature ◽  
Meridional Heat Transport ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
Meridional Overturning

The role of oceanic background diapycnal diffusion for the equilibrium climate state is investigated in the global coupled climate model CM2G. Special emphasis is put on the oceanic meridional overturning and heat transport. Six runs with the model, differing only by their value of the background diffusivity, are run to steady state and the statistically steady integrations are compared. The diffusivity changes have large-scale impacts on many aspects of the climate system. Two examples are the volume-mean potential temperature, which increases by 3.6°C between the least and most diffusive runs, and the Antarctic sea ice extent, which decreases rapidly as the diffusivity increases. The overturning scaling with diffusivity is found to agree rather well with classical theoretical results for the upper but not for the lower cell. An alternative empirical scaling with the mixing energy is found to give good results for both cells. The oceanic meridional heat transport increases strongly with the diffusivity, an increase that can only partly be explained by increases in the meridional overturning. The increasing poleward oceanic heat transport is accompanied by a decrease in its atmospheric counterpart, which keeps the increase in the planetary energy transport small compared to that in the ocean.

scholarly journals Projected Changes in South Asian Monsoon Low Pressure Systems

2020 ◽  
Vol 33 (17) ◽  
pp. 7275-7287 ◽  
Author(s):  
Wenhao Dong ◽  
Yi Ming ◽  
V. Ramaswamy
Keyword(s):  
South Asian ◽  
Large Scale ◽  
Climate Model ◽  
Asian Summer Monsoon ◽  
Central India ◽  
Low Pressure ◽  
Geophysical Fluid Dynamics Laboratory ◽  
South Asian Summer Monsoon ◽  
Projected Changes ◽  
Low Pressure Systems

AbstractMonsoon low pressure systems (MLPSs) are among the most important synoptic-scale disturbances of the South Asian summer monsoon. Potential changes in their characteristics in a warmer climate would have broad societal impacts. Yet, the findings from a few existing studies are inconclusive. We use the Geophysical Fluid Dynamics Laboratory (GFDL) coupled climate model CM4.0 to examine the projected changes in the simulated MLPS activity under a future emission scenario. It is shown that CM4.0 can skillfully simulate the number, genesis location, intensity, and lifetime of MLPSs. Global warming gives rise to a significant decrease in MLPS activity. An analysis of several large-scale environmental variables, both dynamic and thermodynamic, suggests that the decrease in MLPS activity can be attributed mainly to a reduction in low-level relative vorticity over the core genesis region. The decreased vorticity is consistent with weaker large-scale ascent, which leads to less vorticity production through the stretching term in the vorticity equation. Assuming a fixed radius of influence, the projected reduction in MLPSs would significantly lower the associated precipitation over north-central India, despite an overall increase in mean precipitation.

scholarly journals Solsticial Hadley Cell ascending edge theory from supercriticality

2021 ◽  
Author(s):  
Spencer A. Hill ◽  
Simona Bordoni ◽  
Jonathan L. Mitchell
Keyword(s):  
Large Scale ◽  
Analytical Approximation ◽  
Hadley Cell ◽  
Rossby Number ◽  
Absolute Vorticity ◽  
Rotation Rates ◽  
Planetary Rotation ◽  
Wide Range ◽  
Summer Hemisphere ◽  
Earth’S Climate

AbstractHow far the Hadley circulation’s ascending branch extends into the summer hemisphere is a fundamental but incompletely understood characteristic of Earth’s climate. Here, we present a predictive, analytical theory for this ascending edge latitude based on the extent of supercritical forcing. Supercriticality sets the minimum extent of a large-scale circulation based on the angular momentum and absolute vorticity distributions of the hypothetical state were the circulation absent. We explicitly simulate this latitude-by-latitude radiative-convective equilibrium (RCE) state. Its depth-averaged temperature profile is suitably captured by a simple analytical approximation that increases linearly with sinφ, where φ is latitude, from the winter to the summer pole. This, in turn, yields a one-third power-law scaling of the supercritical forcing extent with the thermal Rossby number. In moist and dry idealized GCM simulations under solsticial forcing performed with a wide range of planetary rotation rates, the ascending edge latitudes largely behave according to this scaling.

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.

scholarly journals The GFDL CM3 Coupled Climate Model: Characteristics of the Ocean and Sea Ice Simulations

2011 ◽  
Vol 24 (13) ◽  
pp. 3520-3544 ◽  
Author(s):  
Stephen M. Griffies ◽  
Michael Winton ◽  
Leo J. Donner ◽  
Larry W. Horowitz ◽  
Stephanie M. Downes ◽  
...  
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Climate Model ◽  
Atmospheric Model ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Climate Simulation ◽  
Climate Indices ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Coupled Climate Model

Abstract This paper documents time mean simulation characteristics from the ocean and sea ice components in a new coupled climate model developed at the NOAA Geophysical Fluid Dynamics Laboratory (GFDL). The GFDL Climate Model version 3 (CM3) is formulated with effectively the same ocean and sea ice components as the earlier CM2.1 yet with extensive developments made to the atmosphere and land model components. Both CM2.1 and CM3 show stable mean climate indices, such as large-scale circulation and sea surface temperatures (SSTs). There are notable improvements in the CM3 climate simulation relative to CM2.1, including a modified SST bias pattern and reduced biases in the Arctic sea ice cover. The authors anticipate SST differences between CM2.1 and CM3 in lower latitudes through analysis of the atmospheric fluxes at the ocean surface in corresponding Atmospheric Model Intercomparison Project (AMIP) simulations. In contrast, SST changes in the high latitudes are dominated by ocean and sea ice effects absent in AMIP simulations. The ocean interior simulation in CM3 is generally warmer than in CM2.1, which adversely impacts the interior biases.

Recent atmospheric circulation trends: two major flaws in reanalyses and in climate models

2020 ◽  
Author(s):  
Rei Chemke ◽  
Lorenzo Polvani
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Heat Fluxes ◽  
Hadley Cell ◽  
Polar Regions ◽  
Large Scale Circulation ◽  
Model Simulations ◽  
Eddy Heat Flux

<p>The weakening of the Hadley cell and of the midlatitude eddy heat fluxes are two of the most robust responses of the atmospheric circulation to increasing concentrations of greenhouse gases.  These changes have important global climatic impacts, as the large-scale circulation acts to transfer heat and moisture from the tropics to polar regions.  Here, we examine Hadley cell and eddy heat flux trends in recent decades: contrasting model simulations with reanalyses, we uncover two important flaws -- one in the reanalyses and other in the model simulations -- that have, to date, gone largely unnoticed.<br><br>First, we find that while climate models simulate a weakening of the Hadley cell over the past four decades, most atmospheric reanalyses indicate a considerable strengthening.  Interestingly, that discrepancy does not stem from biases in climate models, but appears to be related to artifacts in the representation of latent heating in the reanalyses.  This suggests that when dealing with the divergent part of the large-scale circulation, reanalyses may be fundamentally unreliable for the calculation of trends, even for trends spanning several decades.<br><br>Second, we examine recent trends in eddy heat fluxes at midlatitudes, which are directly linked the equator-to-pole temperature gradient.  In the Northern Hemisphere models and reanalyses are in good agreement. In the Southern Hemisphere, however, models show a weakening while reanalyses indicate a robust strengthening.  In this case, the flaw is found to be with the climate models, which are unable to simulate the observed multidecadal cooling of the Southern Ocean at high-latitudes, and the accompanying increase in sea-ice.  While the biases in modeled Antarctic sea ice trends have been widely reported, our results demonstrates that such biases have important implications well beyond the high Southern latitudes, as they impact the equator-to-pole temperature and, as a consequence, the midlatitude atmospheric circulation.</p>

Nonlinear Climate Responses to Changes in Antarctic Intermediate Water

2013 ◽  
Vol 26 (22) ◽  
pp. 9175-9193 ◽  
Author(s):  
Jennifer A. Graham ◽  
David P. Stevens ◽  
Karen J. Heywood
Keyword(s):  
Climate Model ◽  
Potential Temperature ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Intermediate Water ◽  
Antarctic Intermediate Water ◽  
Surface Ocean ◽  
The North ◽  
Meridional Overturning ◽  
Circumpolar Current

Abstract The global impact of changes in Antarctic Intermediate Water (AAIW) properties is demonstrated using idealized perturbation experiments in a coupled climate model. Properties of AAIW were altered between 10° and 20°S in the Atlantic, Pacific, and Indian Oceans separately. Potential temperature was changed by ±1°C, along with density-compensating changes in salinity. For each of the experiments, sea surface temperature responds to changes in AAIW when anomalies surface at higher latitudes (>30°). Anomalous sea-to-air heat fluxes leave density anomalies in the ocean, resulting in nonlinear responses to opposite-sign perturbations. In the Southern Ocean, these affect the meridional density gradient, leading to changes in Antarctic Circumpolar Current transport. The response to cooler, fresher AAIW is both greater in magnitude and significant over a larger area than that for warmer, saltier AAIW. The North Atlantic is particularly sensitive to cool, fresh perturbations, with density anomalies causing reductions in the meridional overturning circulation of up to 1 Sv (1 Sv ≡ 106 m3 s−1). Resultant changes in meridional ocean heat transport, along with surfacing anomalies, cause basinwide changes in the surface ocean and overlying atmosphere on multidecadal time scales.

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