scholarly journals Zonal-Mean Atmospheric Dynamics of Slowly Rotating Terrestrial Planets

2019 ◽  
Vol 76 (5) ◽  
pp. 1397-1418
Author(s):  
G. J. Colyer ◽  
G. K. Vallis
Keyword(s):  
Numerical Simulations ◽  
Zonal Wind ◽  
Rotation Rate ◽  
Potential Temperature ◽  
Terrestrial Planet ◽  
Zonal Flow ◽  
Hadley Cell ◽  
Overturning Circulation ◽  
Eddy Motion ◽  
Planetary Rotation

Abstract The zonal-mean atmospheric flow of an idealized terrestrial planet is investigated using both numerical simulations and zonally symmetric theories, focusing largely on the limit of low planetary rotation rate. Two versions of a zonally symmetric theory are considered, the standard Held–Hou model, which features a discontinuous zonal wind at the edge of the Hadley cell, and a variant with continuous zonal wind but discontinuous temperature. The two models have different scalings for the boundary latitude and zonal wind. Numerical simulations are found to have smoother temperature profiles than either model, with no temperature or velocity discontinuities even in zonally symmetric simulations. Continuity is achieved in part by the presence of an overturning circulation poleward of the point of maximum zonal wind, which allows the zonal velocity profile to be smoother than the original theory without the temperature discontinuities of the variant theory. Zonally symmetric simulations generally fall between the two sets of theoretical scalings, and have a faster polar zonal flow than either set. Three-dimensional simulations, which allow for the eddy motion that is missing from both models, fall closer to the scalings of the variant model. At very low rotation rates the maximum zonal wind falls with falling planetary rotation rate, and is zero at zero rotation. The low-rotation limit of the overturning circulation, however, is strong enough to drive the temperature profile close to a state of nearly constant potential temperature.

scholarly journals Axisymmetric Constraints on Cross-Equatorial Hadley Cell Extent

2019 ◽  
Vol 76 (6) ◽  
pp. 1547-1564 ◽  
Author(s):  
Spencer A. Hill ◽  
Simona Bordoni ◽  
Jonathan L. Mitchell
Keyword(s):  
Angular Momentum ◽  
Zonal Wind ◽  
General Circulation ◽  
Potential Temperature ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Hadley Cell ◽  
Equal Area ◽  
Area Model ◽  
Hadley Cells

Abstract We consider the relevance of known constraints from each of Hide’s theorem, the angular momentum–conserving (AMC) model, and the equal-area model on the extent of cross-equatorial Hadley cells. These theories respectively posit that a Hadley circulation must span all latitudes where the radiative–convective equilibrium (RCE) absolute angular momentum satisfies or or where the RCE absolute vorticity satisfies ; all latitudes where the RCE zonal wind exceeds the AMC zonal wind; and over a range such that depth-averaged potential temperature is continuous and that energy is conserved. The AMC model requires knowledge of the ascent latitude , which needs not equal the RCE forcing maximum latitude . Whatever the value of , we demonstrate that an AMC cell must extend at least as far into the winter hemisphere as the summer hemisphere. The equal-area model predicts , always placing it poleward of . As is moved poleward (at a given thermal Rossby number), the equal-area-predicted Hadley circulation becomes implausibly large, while both and become increasingly displaced poleward of the minimal cell extent based on Hide’s theorem (i.e., of supercritical forcing). In an idealized dry general circulation model, cross-equatorial Hadley cells are generated, some spanning nearly pole to pole. All homogenize angular momentum imperfectly, are roughly symmetric in extent about the equator, and appear in extent controlled by the span of supercritical forcing.

scholarly journals Limits on the Extent of the Solsticial Hadley Cell: The Role of Planetary Rotation

2019 ◽  
Vol 76 (7) ◽  
pp. 1989-2004 ◽  
Author(s):  
Martin S. Singh
Keyword(s):  
Rotation Rate ◽  
Seasonal Cycle ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Cell ◽  
Quasi Equilibrium ◽  
Rotation Rates ◽  
Planetary Rotation ◽  
Summer Hemisphere

Abstract The role of planetary rotation in limiting the extent of the cross-equatorial solsticial Hadley cell (SHC) is investigated using idealized simulations with an aquaplanet general circulation model run under perpetual-solstice conditions. Consistent with previous studies that include a seasonal cycle, the SHC extent increases with decreasing rotation rate, and it occupies the entire globe for sufficiently low planetary rotation rates. A simple theory for the summer-hemisphere extent of the SHC is constructed in which it is assumed that the SHC occupies regions for which a hypothetical radiative–convective equilibrium state is physically unattainable. The theory predicts that the SHC extends farther into the summer hemisphere as the rotation rate is decreased, qualitatively reproducing the behavior of the simulations, but it generally underestimates the simulated SHC extent. A diagnostic theory for the summer-hemisphere SHC extent is then developed based on the assumptions of slantwise convective neutrality and conservation of angular momentum within the Hadley cell. The theory relates the structure of the SHC in the summer hemisphere to the distribution of boundary layer entropy in the dynamically equilibrated simulations. The resultant diagnostic for the SHC extent generalizes the convective quasi-equilibrium-based constraint of Privé and Plumb, in which the position of rain belts is related to maxima in the low-level entropy distribution.

scholarly journals Constraints from Invariant Subtropical Vertical Velocities on the Scalings of Hadley Cell Strength and Downdraft Width with Rotation Rate

2021 ◽  
Vol 78 (5) ◽  
pp. 1445-1463
Author(s):  
Jonathan L. Mitchell ◽  
Spencer A. Hill
Keyword(s):  
Heat Flux ◽  
Vertical Velocity ◽  
Rotation Rate ◽  
Diabatic Heating ◽  
Static Stability ◽  
Hadley Cell ◽  
Rossby Number ◽  
Eddy Heat Flux ◽  
Planetary Rotation ◽  
Wide Range

AbstractWeak-temperature-gradient influences from the tropics and quasigeostrophic influences from the extratropics plausibly constrain the subtropical-mean static stability in terrestrial atmospheres. Because mean descent acting on this static stability is a leading-order term in the thermodynamic balance, a state-invariant static stability would impose constraints on the Hadley cells, which this paper explores in simulations of varying planetary rotation rate. If downdraft-averaged effective heating (the sum of diabatic heating and eddy heat flux convergence) too is invariant, so must be vertical velocity—an “omega governor.” In that case, the Hadley circulation overturning strength and downdraft width must scale identically—the cell can strengthen only by widening or weaken only by narrowing. Semiempirical scalings demonstrate that subtropical eddy heat flux convergence weakens with rotation rate (scales positively) while diabatic heating strengthens (scales negatively), compensating one another if they are of similar magnitude. Simulations in two idealized, dry GCMs with a wide range of planetary rotation rates exhibit nearly unchanging downdraft-averaged static stability, effective heating, and vertical velocity, as well as nearly identical scalings of the Hadley cell downdraft width and strength. In one, eddy stresses set this scaling directly (the Rossby number remains small); in the other, eddy stress and bulk Rossby number changes compensate to yield the same, ~Ω−1/3 scaling. The consistency of this power law for cell width and strength variations may indicate a common driver, and we speculate that Ekman pumping could be the mechanism responsible for this behavior. Diabatic heating in an idealized aquaplanet GCM is an order of magnitude larger than in dry GCMs and reanalyses, and while the subtropical static stability is insensitive to rotation rate, the effective heating and vertical velocity are not.

Radiative and Dynamic Controls on Atmospheric Heat Transport over Different Planetary Rotation Rates

2021 ◽  
Vol 34 (9) ◽  
pp. 3543-3554
Author(s):  
Tyler Cox ◽  
Kyle C. Armour ◽  
Gerard H. Roe ◽  
Aaron Donohoe ◽  
Dargan M. W. Frierson
Keyword(s):  
Heat Transport ◽  
Rotation Rate ◽  
Hadley Cell ◽  
Slow Rotation ◽  
Rotation Rates ◽  
Planetary Rotation ◽  
Atmospheric Heat Transport ◽  
Mean Meridional Circulation ◽  
Radiative Temperature ◽  
Atmospheric Heat

AbstractAtmospheric heat transport is an important piece of our climate system, yet we lack a complete theory for its magnitude or changes. Atmospheric dynamics and radiation play different roles in controlling the total atmospheric heat transport (AHT) and its partitioning into components associated with eddies and mean meridional circulations. This work focuses on two specific controls: a radiative one, namely atmospheric radiative temperature tendencies, and a dynamic one, the planetary rotation rate. We use an idealized gray radiation model to employ a novel framework to lock the radiative temperature tendency and total AHT to climatological values, even while the rotation rate is varied. This setup allows for a systematic study of the effects of radiative tendency and rotation rate on AHT. We find that rotation rate controls the latitudinal extent of the Hadley cell and the heat transport efficiency of eddies. Both the rotation rate and radiative tendency influence the strength of the Hadley cell and the strength of equator–pole energy differences that are important for AHT by eddies. These two controls do not always operate independently and can reinforce or dampen each other. In addition, we examine how individual AHT components, which vary with latitude, sum to a total AHT that varies smoothly with latitude. At slow rotation rates the mean meridional circulation is most important in ensuring total AHT varies smoothly with latitude, while eddies are most important at rotation rates similar to, and faster than, those of Earth.

scholarly journals Moist Recirculation and Water Vapor Transport on Dry Isentropes*

2012 ◽  
Vol 69 (3) ◽  
pp. 875-890 ◽  
Author(s):  
Frédéric Laliberté ◽  
Tiffany Shaw ◽  
Olivier Pauluis
Keyword(s):  
Water Vapor ◽  
Potential Temperature ◽  
Hadley Cell ◽  
Vapor Transport ◽  
Storm Tracks ◽  
Water Vapor Transport ◽  
Equivalent Potential Temperature ◽  
Overturning Circulation ◽  
Equivalent Potential ◽  
Mass Fluxes

Abstract An analysis of the overturning circulation in dry isentropic coordinates using reanalysis data is presented. The meridional mass fluxes on surfaces of constant dry potential temperature but distinct equivalent potential temperature are separated into southward and northward contributions. The separation identifies thermodynamically distinct mass fluxes moving in opposite directions. The eddy meridional water vapor transport is shown to be associated with large poleward and equatorward mass fluxes occurring at the same value of dry potential temperature but different equivalent potential temperature. These mass fluxes, referred to here as the moist recirculation, are associated with an export of water vapor from the subtropics connecting the Hadley cell to the midlatitude storm tracks. The poleward branch of the moist recirculation occurs at mean equivalent potential temperatures comparable to upper tropospheric dry potential temperature values, indicating that typical poleward-moving air parcels can ascend to the tropopause. The analysis suggests that these air parcels ascend on the equatorward side of storm tracks by following moist isentropes reminiscent of upright deep convection, while on the poleward side their moist isentropes are indicative of large-scale slantwise convection. In the equatorward branch, the analysis describes typical air parcels that follow their dry isentropes until they get injected into the boundary layer where they are subsequently moistened. The moist recirculation along with the mean equivalent potential temperature of its poleward and equatorward components are used to recover an approximate overturning circulation on moist isentropes from which it is shown that the moist recirculation accounts for the difference between the meridional circulation averaged on dry and on moist isentropes.

scholarly journals Earth-size planet formation in the habitable zone of circumbinary stars

2020 ◽  
Vol 494 (1) ◽  
pp. 1045-1057 ◽  
Author(s):  
G O Barbosa ◽  
O C Winter ◽  
A Amarante ◽  
A Izidoro ◽  
R C Domingos ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Planet Formation ◽  
Terrestrial Planet ◽  
Close Binary ◽  
Habitable Zone ◽  
Density Profiles ◽  
Habitable Planets ◽  
Habitable Zones ◽  
Test Particles ◽  
The Stability

ABSTRACT This work investigates the possibility of close binary (CB) star systems having Earth-size planets within their habitable zones (HZs). First, we selected all known CB systems with confirmed planets (totaling 22 systems) to calculate the boundaries of their respective HZs. However, only eight systems had all the data necessary for the computation of HZ. Then, we numerically explored the stability within HZs for each one of the eight systems using test particles. From the results, we selected five systems that have stable regions inside HZs, namely Kepler-34,35,38,413, and 453. For these five cases of systems with stable regions in HZ, we perform a series of numerical simulations for planet formation considering discs composed of planetary embryos and planetesimals, with two distinct density profiles, in addition to the stars and host planets of each system. We found that in the case of the Kepler-34 and 453 systems, no Earth-size planet is formed within HZs. Although planets with Earth-like masses were formed in Kepler-453, they were outside HZ. In contrast, for the Kepler-35 and 38 systems, the results showed that potentially habitable planets are formed in all simulations. In the case of the Kepler-413system, in just one simulation, a terrestrial planet was formed within HZ.

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.

K–ϵ model for rotating homogeneous decaying turbulence

2016 ◽  
Vol 94 (11) ◽  
pp. 1200-1204 ◽  
Author(s):  
Hamed Marzougui
Keyword(s):  
Kinetic Energy ◽  
Numerical Simulations ◽  
Decay Rate ◽  
Rate Equation ◽  
Rotation Rate ◽  
Dissipation Rate ◽  
Direct Numerical Simulations ◽  
Uniform Rotation ◽  
Axis Of Rotation ◽  
Decaying Turbulence

In the present work, we propose a modification to the standard K–ϵ model for simulating homogeneous decaying turbulence subjected to uniform rotation. In this modification, the dissipation rate equation is formulated in terms of the rotation rate Ω, the integral length scales along the axis of rotation [Formula: see text], and its isotropic value [Formula: see text]. The comparison of our results with the corresponding direct numerical simulations proves that the new model reproduces in an excellent way the decay rate of the turbulent kinetic energy.

scholarly journals The Role of the Divergent Circulation for Large-Scale Eddy Momentum Transport in the Tropics. Part I: Observations

2019 ◽  
Vol 76 (4) ◽  
pp. 1125-1144 ◽  
Author(s):  
Pablo Zurita-Gotor
Keyword(s):  
Momentum Flux ◽  
Large Scale ◽  
Zonal Flow ◽  
Stationary Wave ◽  
Hadley Cell ◽  
Momentum Transport ◽  
Mean Flow ◽  
Meridional Transport ◽  
The Tropics

Abstract This work investigates the role played by the divergent circulation for meridional eddy momentum transport in the tropical atmosphere. It is shown that the eddy momentum flux in the deep tropics arises primarily from correlations between the divergent eddy meridional velocity and the rotational eddy zonal velocity. Consistent with previous studies, this transport is dominated by the stationary wave component, associated with correlations between the zonal structure of the Hadley cell (zonal anomalies in the meridional overturning) and the climatological-mean Rossby gyres. This eddy momentum flux decomposition implies a different mechanism of eddy momentum convergence from the extratropics, associated with upper-level mass convergence (divergence) over sectors with anomalous westerlies (easterlies). By itself, this meridional transport would only increase (decrease) isentropic thickness over regions with anomalous westerly (easterly) zonal flow. The actual momentum mixing is due to vertical (cross isentropic) advection, pointing to the key role of diabatic processes for eddy–mean flow interaction in the tropics.

Delineating the Eddy–Zonal Flow Interaction in the Atmospheric Circulation Response to Climate Forcing: Uniform SST Warming in an Idealized Aquaplanet Model

2013 ◽  
Vol 70 (7) ◽  
pp. 2214-2233 ◽  
Author(s):  
Gang Chen ◽  
Jian Lu ◽  
Lantao Sun
Keyword(s):  
Wave Propagation ◽  
Momentum Flux ◽  
Surface Friction ◽  
Zonal Flow ◽  
Finite Amplitude ◽  
Wave Activity ◽  
Hadley Cell ◽  
Climate Forcing ◽  
Sst Warming ◽  
Poleward Shift

Abstract The mechanisms of the atmospheric response to climate forcing are analyzed using an example of uniform SST warming in an idealized aquaplanet model. A 200-member ensemble of experiments is conducted with an instantaneous uniform SST warming. The zonal mean circulation changes display a rapid poleward shift in the midlatitude eddy-driven westerlies and the edge of the Hadley cell circulation and a slow equatorward contraction of the circulation in the deep tropics. The shift of the poleward edge of the Hadley cell is predominantly controlled by the eddy momentum flux. It also shifts the eddy-driven westerlies against the surface friction, at a rate much faster than the expectation from the natural variability of the eddy-driven jet (i.e., the e-folding time scale of the annular mode), with much less feedback between the eddies and zonal flow. The transient eddy–zonal flow interactions are delineated using a newly developed finite-amplitude wave activity diagnostic of Nakamura. Applying it to the transient ensemble response to uniform SST warming reveals that the eddy-driven westerlies are shifted poleward by permitting more upward wave propagation in the middle and upper troposphere rather than reducing the lower-tropospheric baroclinicity. The increased upward wave propagation is attributed to a reduction in eddy dissipation of wave activity as a result of a weaker meridional potential vorticity (PV) gradient. The reduction allows more waves to propagate away from the latitudes of baroclinic generation, which, in turn, leads to more poleward momentum flux and a poleward shift of eddy-driven winds and Hadley cell edge.

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