scholarly journals Impact of the Warming Pattern on Global Energetics

2012 ◽  
Vol 25 (15) ◽  
pp. 5223-5240 ◽  
Author(s):  
Daniel Hernández-Deckers ◽  
Jin-Song von Storch
Keyword(s):  
Temperature Gradient ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Static Stability ◽  
Meridional Temperature Gradient ◽  
Surface Warming ◽  
Warming Pattern ◽  
Atmospheric Energetics ◽  
The Mean

Abstract The warming pattern due to higher greenhouse gas concentrations is expected to affect the global atmospheric energetics mainly via changes in the (i) meridional temperature gradient and (ii) mean static stability. Changes in surface meridional temperature gradients have been previously regarded as the determining feature for the energetics response, but recent studies suggest that changes in mean static stability may be more relevant than previously thought. This study aims to determine the relative importance of these two effects by comparing the energetics responses due to different warming patterns using a fully coupled atmosphere–ocean general circulation model. By means of an additional diabatic forcing, experiments with different warming patterns are obtained: one with a 2xCO2-like pattern that validates the method, one with only the tropical upper-tropospheric warming, and one with only the high-latitude surface warming. The study’s findings suggest that the dominant aspect of the warming pattern that alters the global atmospheric energetics is not its associated meridional temperature gradient changes, but the mean static stability changes. The tropical upper warming weakens the energetics by increasing the mean static stability, whereas the surface warming strengthens it by reducing the mean static stability. The combined 2xCO2-like response is dominated by the tropical upper-tropospheric warming effect, hence the weaker energetic activity. Eddy kinetic energy changes consistently, but the two opposite responses nearly cancel each other in the 2xCO2 case. Therefore, estimates of future changes in storminess may be particularly sensitive to the relative magnitude of the main features of the simulated warming pattern.

scholarly journals A Geometric Interpretation of Southern Ocean Eddy Form Stress

2019 ◽  
Vol 49 (10) ◽  
pp. 2553-2570 ◽  
Author(s):  
Mads B. Poulsen ◽  
Markus Jochum ◽  
James R. Maddison ◽  
David P. Marshall ◽  
Roman Nuterman
Keyword(s):  
Southern Ocean ◽  
General Circulation ◽  
Vertical Structure ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Geometric Interpretation ◽  
Mean Flow ◽  
Geometric Framework ◽  
The Mean ◽  
Circumpolar Current

AbstractAn interpretation of eddy form stress via the geometry described by the Eliassen–Palm flux tensor is explored. Complimentary to previous works on eddy Reynolds stress geometry, this study shows that eddy form stress is fully described by a vertical ellipse, whose size, shape, and orientation with respect to the mean flow shear determine the strength and direction of vertical momentum transfers. Following a recent proposal, this geometric framework is here used to form a Gent–McWilliams eddy transfer coefficient that depends on eddy energy and a nondimensional geometric parameter α, bounded in magnitude by unity. The parameter α expresses the efficiency by which eddies exchange energy with baroclinic mean flow via along-gradient eddy buoyancy flux—a flux equivalent to eddy form stress along mean buoyancy contours. An eddy-resolving ocean general circulation model is used to estimate the spatial structure of α in the Southern Ocean and assess its potential to form a basis for parameterization. The eddy efficiency α averages to a low but positive value of 0.043 within the Antarctic Circumpolar Current, consistent with an inefficient eddy field extracting energy from the mean flow. It is found that the low eddy efficiency is mainly the result of that eddy buoyancy fluxes are weakly anisotropic on average. The eddy efficiency is subject to pronounced vertical structure and is maximum at ~3-km depth, where eddy buoyancy fluxes tend to be directed most downgradient. Since α partly sets the eddy form stress in the Southern Ocean, a parameterization for α must reproduce its vertical structure to provide a faithful representation of vertical stress divergence and eddy forcing.

Improved Climate Simulation by MIROC5: Mean States, Variability, and Climate Sensitivity

2010 ◽  
Vol 23 (23) ◽  
pp. 6312-6335 ◽  
Author(s):  
Masahiro Watanabe ◽  
Tatsuo Suzuki ◽  
Ryouta O’ishi ◽  
Yoshiki Komuro ◽  
Shingo Watanabe ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
General Circulation ◽  
Southern Oscillation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Climate Simulation ◽  
Mean Fields ◽  
Equatorial Ocean ◽  
The Mean ◽  
The Difference

Abstract A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3.2) with two different resolutions (medres, hires), coarser and finer than the resolution of MIROC5. A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3.2, but otherwise the climatological features are considerably better. In particular, improvements are found in precipitation, zonal mean atmospheric fields, equatorial ocean subsurface fields, and the simulation of El Niño–Southern Oscillation. The difference between MIROC5 and the previous model is larger than that between the two MIROC3.2 versions, indicating a greater effect of updating parameterization schemes on the model climate than increasing the model resolution. The mean cloud property obtained from the sophisticated prognostic schemes in MIROC5 shows good agreement with satellite measurements. MIROC5 reveals an equilibrium climate sensitivity of 2.6 K, which is lower than that in MIROC3.2 by 1 K. This is probably due to the negative feedback of low clouds to the increasing concentration of CO2, which is opposite to that in MIROC3.2.

The Response of an Idealized Atmosphere to Localized Tropical Heating: Superrotation and the Breakdown of Linear Theory

2018 ◽  
Vol 75 (1) ◽  
pp. 3-20 ◽  
Author(s):  
Nicholas J. Lutsko
Keyword(s):  
Temperature Gradient ◽  
General Circulation ◽  
Circulation Model ◽  
Mean Flow ◽  
Heating Rates ◽  
Momentum Fluxes ◽  
The Mean ◽  
The Stability ◽  
The Waves ◽  
Large Heating

An equatorial heat source mimicking the strong diabatic heating above the west Pacific is added to an idealized, dry general circulation model. For small (<0.5 K day−1) heating rates the responses closely match the expectations from linear Matsuno–Gill theory, though the amplitudes of the responses increase sublinearly. This “linear” regime breaks down for larger heating rates and it is found that this is because the stability of the tropical atmosphere increases. At the same time, the equatorial winds increasingly superrotate. This superrotation is driven by stationary eddy momentum fluxes by the waves excited by the heating and is damped by the vertical advection of low-momentum air by the mean flow and, at large heating rates, by the divergence of momentum by transient eddies. These dynamics are explored in additional experiments in which the equator-to-pole temperature gradient is varied. Very strong superrotation is produced when a large heating rate is applied to a setup with a relatively weak equator-to-pole temperature gradient, though there is no evidence that this is a case of “runaway” superrotation.

Dynamical effect on the Venusian thermal structure simulated by a general circulation model

2021 ◽  
Author(s):  
Hiroki Ando ◽  
Kotaro Takaya ◽  
Masahiro Takagi ◽  
Norihiko Sugimoto ◽  
Takeshi Imamura ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Polar Region ◽  
Thermal Structure ◽  
Circulation Model ◽  
Static Stability ◽  
Type Wave ◽  
Low Latitudes ◽  
Mean Meridional Circulation ◽  
The Mean

&lt;div class=&quot;page&quot; title=&quot;Page 2&quot;&gt; &lt;div class=&quot;layoutArea&quot;&gt; &lt;div class=&quot;column&quot;&gt; &lt;p&gt;Distributions of temperature and static stability in the Venus atmosphere consistent with&amp;#160;recent radio occultation measurements are reproduced using a general circulation model.&amp;#160;A low-stability layer is maintained at low- and mid-latitudes at 50&amp;#8211;60 km altitude and&amp;#160;is sandwiched by high- and moderate-stability layers extending above 60 and below 50 &amp;#160;km, respectively. In the polar region, the low-stability layer is located at 46&amp;#8211;63 km altitude and the relatively low-stability layer is also found at 40&amp;#8211;46 km altitude. To investigate how these thermal structures form, we examine the dynamical effects of the atmospheric motions on the static stability below 65 km altitude. The results show that&amp;#160;the heat transport due to the mean meridional circulation is important at low-latitudes.&amp;#160;At mid- and high-latitudes, meanwhile, the baroclinic Rossby-type wave plays an important role in maintaining the thermal structure. In addition, appreciable equatorward heat&amp;#160;transport is found to maintain the deep and low-stability layer in the polar region, which&amp;#160;might be induced by the interaction between the baroclinic Rossby-type wave in the low-stability layer and the trapped Rossby-type wave below it.&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;

Estimating structural and parametric uncertainties in the simulated early Eocene surface warming

2020 ◽  
Author(s):  
Sebastian Steinig ◽  
Fran J. Bragg ◽  
Peter J. Irvine ◽  
Daniel J. Lunt ◽  
Paul J. Valdes
Keyword(s):  
Temperature Gradient ◽  
Boundary Conditions ◽  
Greenhouse Gas ◽  
General Circulation ◽  
Parametric Uncertainty ◽  
General Circulation Models ◽  
Parametric Uncertainties ◽  
Early Eocene ◽  
Meridional Temperature Gradient ◽  
Surface Warming

&lt;p&gt;Simulating the proxy-derived surface warming and reduced meridional temperature gradient of the early Eocene greenhouse climate still represents a challenge for most atmosphere-ocean general circulation models. A profound understanding of uncertainties associated with the respective model results is thereby essential to reliably identify any similarities or misfits to the proxy record. Besides incomplete knowledge of past greenhouse gas concentrations and other boundary conditions, structural and parametric uncertainties are the main factors that determine our confidence in paleoclimate simulation results.&lt;/p&gt;&lt;p&gt;The recent publication of coordinated model experiments that apply identical paleogeographic boundary conditions for key time periods of the early Eocene (DeepMIP) allows a systematic analysis of inter-model differences and therefore of structural uncertainties in the simulated surface warming. Here we additionally explore the parametric uncertainty of the early Eocene climatic optimum (EECO) surface warming within one DeepMIP model. For this we performed perturbed parameter ensemble (PPE) simulations with HadCM3B at different atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations following the DeepMIP protocol. Twenty-one parameter sets based on changes in six atmospheric parameters, a sea-ice parameter and the ocean background diffusivity were branched off from the respective DeepMIP control simulations and integrated for a further 1500 model years. The selected parameter sets are based on previous results demonstrating their ability to simulate a pre-industrial global-mean surface temperature within &amp;#177;2 &amp;#176;C of the standard configuration.&lt;/p&gt;&lt;p&gt;Preliminary results indicate a large spread of the simulated low-latitude surface warming in the PPE and therefore significant changes of the large-scale meridional temperature gradient for the EECO. Some ensemble members develop numerical instabilities at CO&lt;sub&gt;2&lt;/sub&gt; concentrations of 840 ppmv and above, most likely in consequence of high temperatures in the tropical troposphere. We further compare the magnitude of the parametric uncertainty of the HadCM3B perturbation experiments with the structural differences found in the DeepMIP multi-model ensemble and explore the sensitivity of the results to the strength of the applied greenhouse gas forcing. Model skill of the PPE members is tested against the most recent DeepMIP compilations of marine and terrestrial proxy temperatures.&lt;/p&gt;

The Tropospheric Response to Tropical and Subtropical Zonally Asymmetric Torques: Analytical and Idealized Numerical Model Results

2012 ◽  
Vol 69 (1) ◽  
pp. 214-235 ◽  
Author(s):  
Tiffany A. Shaw ◽  
William R. Boos
Keyword(s):  
Temperature Gradient ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Critical Line ◽  
Circulation Model ◽  
General Circulation Models ◽  
Kelvin Wave ◽  
Meridional Temperature Gradient ◽  
Poleward Shift

Abstract The tropospheric response to prescribed tropical and subtropical zonally asymmetric torques, which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection, is investigated. The linear analytical Gill model response to westward upper-tropospheric torques is compared to the response to a midtropospheric heating, which is a familiar point of reference. The response to an equatorial torque projects onto a Kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels. In contrast, the torque and heating both produce Rossby gyres of the same sign to the west of the forcing and the zonal-mean streamfunction responses are identical. When the forcings are shifted into the Northern Hemisphere, the streamfunction responses have opposite signs: there is upwelling in the Southern (Northern) Hemisphere in response to the torque (heating). The nonlinear response to westward torques was explored in idealized general circulation model experiments. In the absence of a large-scale meridional temperature gradient, the response to an equatorial torque was confined to the tropics and was qualitatively similar to the linear solutions. When the torque was moved into the subtropics, the vorticity budget response was similar to a downward control–type balance in the zonal mean. In the presence of a meridional temperature gradient, the response to an equatorial torque involved a poleward shift of the midlatitude tropospheric jet and Ferrel cell. The response in midlatitudes was associated with a poleward shift of the regions of horizontal eddy momentum flux convergence, which coincided with a shift in the upper-tropospheric critical line for baroclinic waves. The shift in the critical line was caused (in part) by the zonal wind response to the prescribed torque, suggesting a possible cause of the response in midlatitudes. Overall, this hierarchy of analytical and numerical results highlights robust aspects of the response to tropical and subtropical zonally asymmetric torques and represents the first step toward understanding the response in fully comprehensive general circulation models.

scholarly journals Generation and Growth Mechanism of the Natal Pulse

2010 ◽  
Vol 40 (7) ◽  
pp. 1597-1612 ◽  
Author(s):  
Motohiko Tsugawa ◽  
Hiroyasu Hasumi
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Mean Flow ◽  
Previous Suggestion ◽  
Agulhas Current ◽  
Horizontal Size ◽  
The Mean ◽  
Anticyclonic Eddies ◽  
Present Simulation

Abstract The Natal pulses, solitary cyclonic meanders in the Agulhas Current, are reproduced in an ocean general circulation model. The model covers the region around the Agulhas Current with a grid fine enough to reproduce major eddies. The features of the reproduced Natal pulses are consistent with observational evidences in the following respects: they are generated at the Natal Bight when anticyclonic eddies come, move downstream along the Agulhas Current at speeds about 20 km day−1, and grow in its horizontal size as they move. The present simulation shows that the generation and growth of the Natal pulse occurs because of the interaction between the mean flow of the Agulhas Current and an anticyclonic eddy. A supplemental simulation, where the topography of the Natal Bight is modified, indicates that the topography of the Natal Bight does not cause the generation of the Natal pulses, contrary to a previous suggestion.

Response of the tropical Pacific Ocean to wind changes related to global warming from simulations with an ocean general circulation model

2016 ◽  
Vol 1 (1) ◽  
Author(s):  
Yiyong Luo
Keyword(s):  
Heat Flux ◽  
Wind Speed ◽  
Wind Stress ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Surface Warming ◽  
Equatorial Thermocline ◽  
Ocean General Circulation ◽  
The Tropical Pacific

A suite of numerical experiments is implemented with an ocean general circulation model (OGCM) to ex-amine the roles of wind stress and wind speed for oceanic changes in the tropical Pacific under global warming. In particular, we turned off the changes of wind stress and/or wind speed in the model to identify the effects of wind-driven ocean circulation and air-sea latent heat flux (i.e., its portion through the wind speed influence on the efficiency of latent heat flux). Results show that 1) the wind stress change appears to be a key forcing mechanism for weakening the tropical surface currents as well as for the oceanic changes in the equatorial thermocline, while it only contributes secondarily to the sea surface temperature (SST) pattern formation in the tropics; 2) the wind speed change is the leading cause for the minimum warming over the southeast subtropics and for a stronger surface warming in the northern hemisphere than in the southern hemisphere; and 3) the enhanced surface warming along the equator is mainly due to the effect of warming in the absence of wind stress and wind speed changes, and this effect also plays a significant role for changing the equatorial thermocline.

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