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

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.

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

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3553.1 ◽

2011 ◽

Vol 68 (4) ◽

pp. 769-783 ◽

Cited By ~ 65

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.

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

Journal of Climate ◽

10.1175/jcli-d-17-0402.1 ◽

2018 ◽

Vol 31 (6) ◽

pp. 2417-2434 ◽

Cited By ~ 6

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.

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Baroclinic Eddies and the Extent of the Hadley Circulation: An Idealized GCM Study

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0152.1 ◽

2015 ◽

Vol 72 (7) ◽

pp. 2744-2761 ◽

Cited By ~ 39

Author(s):

Xavier J. Levine ◽

Tapio Schneider

Keyword(s):

General Circulation ◽

Circulation Model ◽

Hadley Circulation ◽

Static Stability ◽

Temperature Gradients ◽

Convective Heating ◽

Wide Range ◽

Poleward Shift ◽

Temperature Contrast ◽

Effective Stability

The Hadley circulation has widened over the past 30 years. This widening has been qualitatively reproduced in general circulation model (GCM) simulations of a warming climate. Comprehensive GCM studies suggest this widening may be caused by a poleward shift in baroclinic eddy activity. Yet the limited amplitude of the climate change signals analyzed so far precludes a quantitative comparison with theories. This study uses two idealized GCMs, one with and one without an active hydrologic cycle, to investigate changes in the extent of the Hadley circulation over a wide range of climates. The climates span global-mean temperatures from 243 to 385 K and equator-to-pole temperature contrasts from 12 to 100 K. Baroclinic eddies control the extent of the Hadley circulation across most of these climates. A supercriticality criterion that quantifies the depth of baroclinic eddies relative to that of the troposphere turns out to be a good indicator of where baroclinic eddies become deep enough to terminate the Hadley circulation. The supercriticality depends on meridional temperature gradients and an effective stability that accounts for the effect of convective heating on baroclinic eddies. As the equator-to-pole temperature contrast weakens or the convective static stability increases, convective heating increasingly influences the thermal stratification of the troposphere and the supercriticality. Consistent with the supercriticality criterion, the Hadley circulation contracts as meridional temperature gradients increase, and it widens as the effective static stability increases. The former occurs during El Niño and may account for the observed Hadley circulation contraction then; the latter occurs during global warming.

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

Journal of Climate ◽

10.1175/2011jcli4104.1 ◽

2011 ◽

Vol 24 (16) ◽

pp. 4368-4384 ◽

Cited By ~ 208

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.

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Changes in the Extratropical Storm Tracks in Response to Changes in SST in an AGCM

Journal of Climate ◽

10.1175/jcli-d-11-00174.1 ◽

2012 ◽

Vol 25 (6) ◽

pp. 1854-1870 ◽

Cited By ~ 37

Author(s):

Lise Seland Graff ◽

J. H. LaCasce

Keyword(s):

Boundary Conditions ◽

General Circulation ◽

Lower Boundary ◽

Storm Track ◽

Circulation Model ◽

Hadley Circulation ◽

Meridional Overturning Circulation ◽

Storm Tracks ◽

Poleward Shift ◽

The Mean

Abstract A poleward shift in the extratropical storm tracks has been identified in observational and climate simulations. The authors examine the role of altered sea surface temperatures (SSTs) on the storm-track position and intensity in an atmospheric general circulation model (AGCM) using realistic lower boundary conditions. A set of experiments was conducted in which the SSTs where changed by 2 K in specified latitude bands. The primary profile was inspired by the observed trend in ocean temperatures, with the largest warming occurring at low latitudes. The response to several other heating patterns was also investigated, to examine the effect of imposed gradients and low- versus high-latitude heating. The focus is on the Northern Hemisphere (NH) winter, averaged over a 20-yr period. Results show that the storm tracks respond to changes in both the mean SST and SST gradients, consistent with previous studies employing aquaplanet (water only) boundary conditions. Increasing the mean SST strengthens the Hadley circulation and the subtropical jets, causing the storm tracks to intensify and shift poleward. Increasing the SST gradient at midlatitudes similarly causes an intensification and a poleward shift of the storm tracks. Increasing the gradient in the tropics, on the other hand, causes the Hadley cells to contract and the storm tracks to shift equatorward. Consistent shifts are seen in the mean zonal velocity, the atmospheric baroclinicity, the eddy heat and momentum fluxes, and the atmospheric meridional overturning circulation. The results support the idea that oceanic heating could be a contributing factor to the observed shift in the storm tracks.

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The Multidecadal Variability of the Asymmetric Mode of the Boreal Autumn Hadley Circulation and Its Link to the Atlantic Multidecadal Oscillation

Journal of Climate ◽

10.1175/jcli-d-15-0025.1 ◽

2016 ◽

Vol 29 (15) ◽

pp. 5625-5641 ◽

Cited By ~ 23

Author(s):

Yipeng Guo ◽

Jianping Li ◽

Juan Feng ◽

Fei Xie ◽

Cheng Sun ◽

...

Keyword(s):

General Circulation ◽

Circulation Model ◽

Hadley Circulation ◽

Atlantic Multidecadal Oscillation ◽

Meridional Wind ◽

Vertical Shear ◽

Asymmetric Mode ◽

Multidecadal Variability ◽

Four Seasons ◽

Precipitation Difference

Abstract Previous studies show that the first principal mode of the variability of the seasonal mean Hadley circulation (HC) is an equatorial asymmetric mode (AM) with long-term trend. This study demonstrates that the variability of the boreal autumn [September–November (SON)] HC is also dominated by an AM, but with multidecadal variability. The SON AM has ascending and descending branches located at approximately 20°N and 20°S, respectively, and explains about 40% of the total variance. Further analysis reveals that the AM is closely linked to the Atlantic multidecadal oscillation (AMO), which is associated with a large cross-equatorial sea surface temperature (SST) gradient and sea level pressure (SLP) gradient. The cross-equatorial thermal contrast further induces an equatorial asymmetric HC anomaly. Numerical simulations conducted on an atmospheric general circulation model also suggest that AMO-associated SST anomalies can also induce a cross-equatorial SLP gradient and anomalous vertical shear of the meridional wind at the equator, both of which indicate asymmetric HC anomaly. Therefore, the AM of the variability of the boreal autumn HC has close links to the AMO. Further analysis demonstrates that the AMO in SON has a closer relationship with AM than those in the other seasons. A possible reason is that the AMO-associated zonal mean SST anomaly in the tropics has differences among the four seasons, which leads to different atmospheric circulation responses. The AM in SON has inversed impacts on the tropical precipitation, suggesting that the precipitation difference between the northern and southern tropics has multidecadal variability.

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

Journal of Climate ◽

10.1175/2007jcli1754.1 ◽

2008 ◽

Vol 21 (3) ◽

pp. 561-575 ◽

Cited By ~ 37

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.

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Storm Track Shifts under Climate Change: What Can Be Learned from Large-Scale Dry Dynamics

Journal of Climate ◽

10.1175/jcli-d-13-00404.1 ◽

2013 ◽

Vol 26 (24) ◽

pp. 9923-9930 ◽

Cited By ~ 35

Author(s):

Cheikh Mbengue ◽

Tapio Schneider

Keyword(s):

Climate Change ◽

General Circulation ◽

Large Scale ◽

Storm Track ◽

Circulation Model ◽

Hadley Circulation ◽

Phase Changes ◽

Storm Tracks ◽

Convective Stability ◽

Poleward Shift

Abstract Earth’s storm tracks are instrumental for transporting heat, momentum, and moisture and thus strongly influence the surface climate. Climate models, supported by a growing body of observational data, have demonstrated that storm tracks shift poleward as the climate warms. But the dynamical mechanisms responsible for this shift remain unclear. To isolate what portion of the storm track shift may be accounted for by large-scale dry dynamics alone, disregarding the latent heat released in phase changes of water, this study investigates the storm track shift under various kinds of climate change in an idealized dry general circulation model (GCM) with an adjustable but constant convective stability. It is found that increasing the mean surface temperature or the convective stability leads to poleward shifts of storm tracks, even if the convective stability is increased only in a narrow band around the equator. Under warming and convective stability changes roughly corresponding to a doubling of CO2 concentrations from a present-day Earthlike climate, storm tracks shift about 0.8° poleward, somewhat less than but in qualitative agreement with studies using moist GCMs. About 63% (0.5°) of the poleward shift is shown to be caused by tropical convective stability variations. This demonstrates that tropical processes alone (the increased dry static stability of a warmer moist adiabat) can account for part of the poleward shift of storm tracks under global warming. This poleward shift generally occurs in tandem with a poleward expansion of the Hadley circulation; however, the Hadley circulation expansion does not always parallel the storm track shift.

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Climate Sensitivity to Changes in Ocean Heat Transport

Journal of Climate ◽

10.1175/jcli-d-10-05029.1 ◽

2011 ◽

Vol 24 (19) ◽

pp. 5015-5030 ◽

Cited By ~ 7

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.

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Hadley Circulation Response to Orbital Precession. Part II: Subtropical Continent

Journal of Climate ◽

10.1175/jcli-d-12-00149.1 ◽

2013 ◽

Vol 26 (3) ◽

pp. 754-771 ◽

Cited By ~ 26

Author(s):

Timothy M. Merlis ◽

Tapio Schneider ◽

Simona Bordoni ◽

Ian Eisenman

Keyword(s):

Land Surface ◽

General Circulation ◽

Atmospheric General Circulation Model ◽

Circulation Model ◽

Hadley Circulation ◽

Surface Heat ◽

Atmospheric General Circulation ◽

Momentum Fluxes ◽

Poleward Shift ◽

Orbital Precession

Abstract The response of the monsoonal and annual-mean Hadley circulation to orbital precession is examined in an idealized atmospheric general circulation model with a simplified representation of land surface processes in subtropical latitudes. When perihelion occurs in the summer of a hemisphere with a subtropical continent, changes in the top-of-atmosphere energy balance, together with a poleward shift of the monsoonal circulation boundary, lead to a strengthening of the monsoonal circulation. Spatial variations in surface heat capacity determine whether radiative perturbations are balanced by energy storage or by atmospheric energy fluxes. Although orbital precession does not affect annual-mean insolation, the annual-mean Hadley circulation does respond to orbital precession because its sensitivity to radiative changes varies over the course of the year: the monsoonal circulation in summer is near the angular momentum-conserving limit and responds directly to radiative changes; whereas in winter, the circulation is affected by the momentum fluxes of extratropical eddies and is less sensitive to radiative changes.

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