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Adam P. Showman - One of the best experts on this subject based on the ideXlab platform.

  • atmospheric circulation of tidally locked gas giants with increasing Rotation and implications for white dwarf brown dwarf systems
    The Astrophysical Journal, 2020
    Co-Authors: Xianyu Tan, Adam P. Showman
    Abstract:

    Tidally locked gas giants are typically in several-day orbits, implying a modest role for Rotation in the atmospheric circulation. Nevertheless, there exist a class of gas-giant, highly irradiated objects---brown dwarfs orbiting white dwarfs in extremely tight orbits---whose orbital and hence Rotation periods are as short as 1-2 hours. Phase curves and other observations have already been obtained for this class of objects, raising fundamental questions about the role of increasing Planetary Rotation rate in controlling the circulation. So far, most modeling studies have investigated Rotation periods exceeding a day, as appropriate for typical hot Jupiters. Here we investigate atmospheric circulation of tidally locked atmospheres with decreasing Rotation periods down to 2.5 hours. With decreasing Rotation period, the width of the equatorial eastward jet decreases, consistent with the narrowing of the equatorial waveguide due to a decrease of the equatorial deformation radius. The eastward-shifted equatorial hot spot offset decreases accordingly, and the off-equatorial westward-shifted hot areas become increasingly distinctive. At high latitudes, winds become weaker and more Rotationally dominated. The day-night temperature contrast becomes larger due to the stronger influence of Rotation. Our simulated atmospheres exhibit variability, presumably caused by instabilities and wave interactions. Unlike typical hot Jupiter models, thermal phase curves of rapidly rotating models show a near alignment of peak flux to secondary eclipse. This result helps to explain why, unlike hot Jupiters, many brown dwarfs orbiting white dwarfs exhibit IR flux peaks aligned with secondary eclipse. Our results have important implications for understanding fast-rotating, tidally locked atmospheres.

  • SuperRotation in Planetary Atmospheres
    Space Science Reviews, 2020
    Co-Authors: Takeshi Imamura, Adam P. Showman, Yohai Kaspi, Jonathan Mitchell, Sebastien Lebonnois, Oleg Korablev
    Abstract:

    SuperRotation is a dynamical regime where the atmosphere circulates around the planet in the direction of Planetary Rotation with excess angular momentum in the equatorial region. SuperRotation is known to exist in the atmospheres of Venus, Titan, Jupiter, and Saturn in the solar system. Some of the exoplanets also exhibit superRotation. Our understanding of superRotation in a framework of circulation regimes of the atmospheres of terrestrial planets is in progress thanks to the development of numerical models; a global instability involving Planetary-scale waves seems to play a key role, and the dynamical state depends on the Rossby number, a measure of the relative importance of the inertial and Coriolis forces, and the thermal inertia of the atmosphere. Recent general circulation models of Venus’s and Titan’s atmospheres demonstrated the importance of horizontal waves in the angular momentum transport in these atmospheres and also an additional contribution of thermal tides in Venus’s atmosphere. The atmospheres of Jupiter and Saturn also exhibit strong superRotation. Recent gravity data suggests that these superRotational flows extend deep into the planet, yet currently no single mechanism has been identified as driving this superRotation. Moreover, atmospheric circulation models of tidally locked, strongly irradiated exoplanets have long predicted the existence of equatorial superRotation in their atmospheres, which has been attributed to the result of the strong day-night thermal forcing. As predicted, recent Doppler observations and infrared phase curves of hot Jupiters appear to confirm the presence of superRotation on these objects.

  • atmospheric dynamics of terrestrial exoplanets over a wide range of orbital and atmospheric parameters
    The Astrophysical Journal, 2015
    Co-Authors: Yohai Kaspi, Adam P. Showman
    Abstract:

    The recent discoveries of terrestrial exoplanets and super-Earths extending over a broad range of orbital and physical parameters suggest that these planets will span a wide range of climatic regimes. Characterization of the atmospheres of warm super-Earths has already begun and will be extended to smaller and more distant planets over the coming decade. The habitability of these worlds may be strongly affected by their three-dimensional atmospheric circulation regimes, since the global climate feedbacks that control the inner and outer edges of the habitable zone—including transitions to Snowball-like states and runaway-greenhouse feedbacks—depend on the equator-to-pole temperature differences, patterns of relative humidity, and other aspects of the dynamics. Here, using an idealized moist atmospheric general circulation model including a hydrological cycle, we study the dynamical principles governing the atmospheric dynamics on such planets. We show how the Planetary Rotation rate, stellar flux, atmospheric mass, surface gravity, optical thickness, and Planetary radius affect the atmospheric circulation and temperature distribution on such planets. Our simulations demonstrate that equator-to-pole temperature differences, meridional heat transport rates, structure and strength of the winds, and the hydrological cycle vary strongly with these parameters, implying that the sensitivity of the planet to global climate feedbacks will depend significantly on the atmospheric circulation. We elucidate the possible climatic regimes and diagnose the mechanisms controlling the formation of atmospheric jet streams, Hadley and Ferrel cells, and latitudinal temperature differences. Finally, we discuss the implications for understanding how the atmospheric circulation influences the global climate.

  • atmospheric circulation of brown dwarfs jets vortices and time variability
    The Astrophysical Journal, 2014
    Co-Authors: Xi Zhang, Adam P. Showman
    Abstract:

    A variety of observational evidence demonstrates that brown dwarfs exhibit active atmospheric circulations. In this study we use a shallow-water model to investigate the global atmospheric dynamics in the stratified layer overlying the convective zone on these rapidly rotating objects. We show that the existence and properties of the atmospheric circulation crucially depend on key parameters including the energy injection rate and radiative timescale. Under conditions of strong internal heat flux and weak radiative dissipation, a banded flow pattern comprised of east-west jet streams spontaneously emerges from the interaction of atmospheric turbulence with the Planetary Rotation. In contrast, when the internal heat flux is weak and/or radiative dissipation is strong, turbulence injected into the atmosphere damps before it can self-organize into jets, leading to a flow dominated by transient eddies and isotropic turbulence instead. The simulation results are not very sensitive to the form of the forcing. Based on the location of the transition between jet-dominated and eddy-dominated regimes, we suggest that many brown dwarfs may exhibit atmospheric circulations dominated by eddies and turbulence (rather than jets) due to the strong radiative damping on these worlds, but a jet structure is also possible under some realistic conditions. Our simulated light curves capture important features from observed infrared light curves of brown dwarfs, including amplitude variations of a few percent and shapes that fluctuate between single-peak and multi-peak structures. More broadly, our work shows that the shallow-water system provides a useful tool to illuminate fundamental aspects of the dynamics on these worlds.

  • atmospheric circulation of exoplanets
    arXiv: Earth and Planetary Astrophysics, 2009
    Co-Authors: Adam P. Showman, Kristen Menou
    Abstract:

    We survey the basic principles of atmospheric dynamics relevant to explaining existing and future observations of exoplanets, both gas giant and terrestrial. Given the paucity of data on exoplanet atmospheres, our approach is to emphasize fundamental principles and insights gained from Solar-System studies that are likely to be generalizable to exoplanets. We begin by presenting the hierarchy of basic equations used in atmospheric dynamics, including the Navier-Stokes, primitive, shallow-water, and two-dimensional nondivergent models. We then survey key concepts in atmospheric dynamics, including the importance of Planetary Rotation, the concept of balance, and scaling arguments to show how turbulent interactions generally produce large-scale east-west banding on rotating planets. We next turn to issues specific to giant planets, including their expected interior and atmospheric thermal structures, the implications for their wind patterns, and mechanisms to pump their east-west jets. Hot Jupiter atmospheric dynamics are given particular attention, as these close-in planets have been the subject of most of the concrete developments in the study of exoPlanetary atmospheres. We then turn to the basic elements of circulation on terrestrial planets as inferred from Solar-System studies, including Hadley cells, jet streams, processes that govern the large-scale horizontal temperature contrasts, and climate, and we discuss how these insights may apply to terrestrial exoplanets. Although exoplanets surely possess a greater diversity of circulation regimes than seen on the planets in our Solar System, our guiding philosophy is that the multi-decade study of Solar-System planets reviewed here provides a foundation upon which our understanding of more exotic exoPlanetary meteorology must build.

Xianyu Tan - One of the best experts on this subject based on the ideXlab platform.

  • atmospheric circulation of tidally locked gas giants with increasing Rotation and implications for white dwarf brown dwarf systems
    The Astrophysical Journal, 2020
    Co-Authors: Xianyu Tan, Adam P. Showman
    Abstract:

    Tidally locked gas giants are typically in several-day orbits, implying a modest role for Rotation in the atmospheric circulation. Nevertheless, there exist a class of gas-giant, highly irradiated objects---brown dwarfs orbiting white dwarfs in extremely tight orbits---whose orbital and hence Rotation periods are as short as 1-2 hours. Phase curves and other observations have already been obtained for this class of objects, raising fundamental questions about the role of increasing Planetary Rotation rate in controlling the circulation. So far, most modeling studies have investigated Rotation periods exceeding a day, as appropriate for typical hot Jupiters. Here we investigate atmospheric circulation of tidally locked atmospheres with decreasing Rotation periods down to 2.5 hours. With decreasing Rotation period, the width of the equatorial eastward jet decreases, consistent with the narrowing of the equatorial waveguide due to a decrease of the equatorial deformation radius. The eastward-shifted equatorial hot spot offset decreases accordingly, and the off-equatorial westward-shifted hot areas become increasingly distinctive. At high latitudes, winds become weaker and more Rotationally dominated. The day-night temperature contrast becomes larger due to the stronger influence of Rotation. Our simulated atmospheres exhibit variability, presumably caused by instabilities and wave interactions. Unlike typical hot Jupiter models, thermal phase curves of rapidly rotating models show a near alignment of peak flux to secondary eclipse. This result helps to explain why, unlike hot Jupiters, many brown dwarfs orbiting white dwarfs exhibit IR flux peaks aligned with secondary eclipse. Our results have important implications for understanding fast-rotating, tidally locked atmospheres.

M K Dougherty - One of the best experts on this subject based on the ideXlab platform.

  • Saturn's auroral field-aligned currents: observations from the Northern Hemisphere dawn sector during cassini's proximal orbits
    'American Geophysical Union (AGU)', 2020
    Co-Authors: Gj Hunt, M K Dougherty, E J Bunce, Cao H, Cowley Swh, Provan G, Dj Southwood
    Abstract:

    We examine the azimuthal magnetic field signatures associated with Saturn's northern hemisphere auroral field‐aligned currents observed in the dawn sector during Cassini's Proximal orbits (April 2017 and September 2017). We compare these currents with observations of the auroral currents from near noon taken during the F‐ring orbits prior to the Proximal orbits. First, we show that the position of the main auroral upward current is displaced poleward between the two local times (LT). This is consistent with the statistical position of the ultraviolet auroral oval for the same time interval. Second, we show the overall average ionospheric meridional current profile differs significantly on the equatorward boundary of the upward current with a swept‐forward configuration with respect to Planetary Rotation present at dawn. We separate the Planetary period oscillation (PPO) currents from the PPO‐independent currents and show their positional relationship is maintained as the latitude of the current shifts in LT implying an intrinsic link between the two systems. Focusing on the individual upward current sheets pass‐by‐pass we find that the main upward current at dawn is stronger compared to near‐noon. This results in the current density been ~1.4 times higher in the dawn sector. We determine a proxy for the precipitating electron power and show that the dawn PPO‐independent upward current electron power ~1.9 times higher than at noon. These new observations of the dawn auroral region from the Proximal orbits may show evidence of an additional upward current at dawn likely associated with strong flows in the outer magnetosphere

  • the periodic flapping and breathing of saturn s magnetodisk during equinox
    Journal of Geophysical Research, 2018
    Co-Authors: Arianna Sorba, N Achilleos, P Guio, C S Arridge, N Sergis, M K Dougherty
    Abstract:

    Periodic variations have been observed in many field and particle properties in Saturn's magnetosphere, modulated at a period close to the Planetary Rotation rate. Magnetic field observations by Cassini's magnetometer instrument suggest that in the outer magnetosphere (beyond ∼12 Saturn radii) Saturn's current sheet is periodically displaced with respect to the Rotational equator, to a first approximation acting as a rotating, tilted disk. This manifests as a “flapping” mode when observed by the spacecraft. Recent studies suggest the magnetosphere also has a “breathing” mode, expanding and contracting with a period close to the Planetary Rotation rate. We model these two modes in tandem by combining a global, geometrical model of a tilted and rippled current sheet with a local, force-balance model of Saturn's magnetodisk, accounting for the magnetospheric size and hot plasma content. We simulate the breathing behavior by introducing an azimuthal dependence of the system size. We fit Cassini magnetometer data acquired on equatorial orbits from 23 October to 17 December 2009 (Revs 120–122), close to Saturn equinox, in order that seasonal effects on the current sheet are minimized. We find that our model characterizes well the amplitude and phase of the oscillations in the data, for those passes that show clear periodic signatures in the field. In particular, the Bθ (meridional) component can only be characterized when the breathing mode is included. This study introduces calculations for an oscillating boundary, which provide a basis for understanding the complex relationship between current sheet dynamics and the periodic field perturbations. ©2018. The Authors.

  • Planetary period oscillations in saturn s magnetosphere evidence in magnetic field phase data for Rotational modulation of saturn kilometric radiation emissions
    Journal of Geophysical Research, 2011
    Co-Authors: D J Andrews, M K Dougherty, S W H Cowley, B Cecconi, L Lamy, G Provan, P Zarka
    Abstract:

    [1] Initial Voyager observations of Saturn kilometric radiation (SKR) indicated that the modulations in emitted power near the ∼11 h Planetary Rotation period are “strobe like,” varying with a phase independent of observer position, while subsequent Cassini studies of related oscillations in the magnetospheric magnetic field and plasma parameters have shown that these rotate around the planet with a period close to the SKR period. However, analysis of magnetic oscillation data over the interval 2004–2010 reveals the presence of variable secular drifts between the phases of the dominant southern period magnetic oscillations and SKR modulations, which become very marked after Cassini apoapsis moved for the first time into the postdusk sector in mid-2009. Here we use a simple theoretical model to show that such phase drifts arise if the SKR modulation phase also rotates around the auroral oval, combined with a highly restricted view of the SKR sources by the spacecraft due to the conical beaming of the emissions. Strobe-like behavior then occurs in the predawn-to-noon sector where the spacecraft has a near-continuous view of the most intense midmorning SKR sources, in agreement with the Voyager findings, while elsewhere the SKR modulation phase depends strongly on spacecraft local time, being in approximate antiphase with the midmorning sources in the postdusk sector. Supporting evidence for this scenario is provided through an independent determination of the variable Rotation period of the southern magnetic field perturbations throughout the 6 year interval.

  • saturn s internal Planetary magnetic field
    Geophysical Research Letters, 2010
    Co-Authors: M E Burton, M K Dougherty, C T Russell
    Abstract:

    [1] A model of Saturn's internal Planetary magnetic field based on data from the Cassini prime mission has been derived. In the absence of a determination of the Rotation rate, the model is constrained to be axisymmetric. Non-axisymmetric models for a range of plausible Planetary Rotation periods have also been derived and we evaluate upper limits on the asymmetry of the internal magnetic field based on those models. We investigate whether a maximum in the non-axisymmetric magnetic field can be identified at a particular Rotation rate thus providing insight into the Rotation rate of the planet's interior. No such peak can unambiguously be identified. An axisymmetric octupole model is adequate to fit the data and addition of higher order terms does not improve the goodness of fit. The largest value of the dipole tilt obtained from non-axisymmetric models (<0.1°) confirm the high degree of symmetry of Saturn's magnetic field.

  • on the character and distribution of lower frequency radio emissions at saturn and their relationship to substorm like events
    Journal of Geophysical Research, 2009
    Co-Authors: C M Jackman, S W H Cowley, B Cecconi, P Zarka, L Lamy, M P Freeman, W S Kurth, M K Dougherty
    Abstract:

    [1] With the arrival of the Cassini spacecraft at Saturn in July 2004, there have been quasi-continuous observations of Saturn kilometric radiation (SKR) emissions. Exploration of the nightside magnetosphere has revealed evidence of plasmoid-like magnetic structures and other phenomena indicative of the Kronian equivalent of terrestrial substorms. In general, there is a good correlation between the timing of reconnection events and enhancements in the auroral SKR emission. Eight of nine reconnection events studied occur at SKR phases where the SKR power would be expected to be rising with time. Thus, while the recurrence rate of substorm-like events at Saturn is likely much longer than the Planetary Rotation timescale, the events are favored to occur at a particular phase of the Rotation. We show three examples in each of which the SKR spectrum extends to lower frequencies than usual. This can be interpreted as an expansion of the auroral particle acceleration region to higher altitudes along magnetic field lines as a direct consequence of an increase in the magnetosphere-ionosphere current density driven by substorm-like events. We then conduct a survey of such low-frequency extensions during the equatorial orbits of 2005–2006 and place some constraints on visibility of these radio emissions.

S W H Cowley - One of the best experts on this subject based on the ideXlab platform.

  • the latitudinal structure of the nightside outer magnetosphere of saturn as revealed by velocity moments of thermal ions
    Annales Geophysicae, 2015
    Co-Authors: Zoltan Nemeth, S W H Cowley, G Provan, K Szego, L Foldy, M G Kivelson, Xianzhe Jia, K M Ramer, M F Thomsen
    Abstract:

    Abstract. In this study we investigate the latitudinal behavior of the azimuthal plasma velocities in the outer magnetosphere of Saturn using the numerical ion moments derived from the measurements of the Cassini Plasma Spectrometer. One of the new results presented is that although these moments display some scatter, a significant positive correlation is found to exist between the azimuthal velocity and the plasma density, such that on average, the higher the density the higher the Rotation speed. We also found that both the azimuthal velocity and the density anticorrelate with the magnitude of the radial component of the magnetic field and drop rapidly with increasing distance from the magnetic equator. The azimuthal velocities show periodic behavior with a period near the Planetary Rotation period, which can also be explained by the strong dependence on magnetic latitude, taking into account the flapping of the magnetodisk. It is thus found that the dense plasma near the magnetic equator rotates around the planet at high speed, while the dilute plasma at higher latitudes in the northern and southern hemispheres rotates significantly slower. The latitudinal gradient observed in the azimuthal speed is suggested to be a direct consequence of the sub-coRotation of the plasma in the outer magnetosphere, with highest speeds occurring on field lines at lowest latitudes mapping to the rapidly rotating inner regions of the plasma sheet, and the speed falling as one approaches the lobe, where the field lines are connected to strongly sub-corotating plasma.

  • Planetary period oscillations in saturn s magnetosphere evidence in magnetic field phase data for Rotational modulation of saturn kilometric radiation emissions
    Journal of Geophysical Research, 2011
    Co-Authors: D J Andrews, M K Dougherty, S W H Cowley, B Cecconi, L Lamy, G Provan, P Zarka
    Abstract:

    [1] Initial Voyager observations of Saturn kilometric radiation (SKR) indicated that the modulations in emitted power near the ∼11 h Planetary Rotation period are “strobe like,” varying with a phase independent of observer position, while subsequent Cassini studies of related oscillations in the magnetospheric magnetic field and plasma parameters have shown that these rotate around the planet with a period close to the SKR period. However, analysis of magnetic oscillation data over the interval 2004–2010 reveals the presence of variable secular drifts between the phases of the dominant southern period magnetic oscillations and SKR modulations, which become very marked after Cassini apoapsis moved for the first time into the postdusk sector in mid-2009. Here we use a simple theoretical model to show that such phase drifts arise if the SKR modulation phase also rotates around the auroral oval, combined with a highly restricted view of the SKR sources by the spacecraft due to the conical beaming of the emissions. Strobe-like behavior then occurs in the predawn-to-noon sector where the spacecraft has a near-continuous view of the most intense midmorning SKR sources, in agreement with the Voyager findings, while elsewhere the SKR modulation phase depends strongly on spacecraft local time, being in approximate antiphase with the midmorning sources in the postdusk sector. Supporting evidence for this scenario is provided through an independent determination of the variable Rotation period of the southern magnetic field perturbations throughout the 6 year interval.

  • on the character and distribution of lower frequency radio emissions at saturn and their relationship to substorm like events
    Journal of Geophysical Research, 2009
    Co-Authors: C M Jackman, S W H Cowley, B Cecconi, P Zarka, L Lamy, M P Freeman, W S Kurth, M K Dougherty
    Abstract:

    [1] With the arrival of the Cassini spacecraft at Saturn in July 2004, there have been quasi-continuous observations of Saturn kilometric radiation (SKR) emissions. Exploration of the nightside magnetosphere has revealed evidence of plasmoid-like magnetic structures and other phenomena indicative of the Kronian equivalent of terrestrial substorms. In general, there is a good correlation between the timing of reconnection events and enhancements in the auroral SKR emission. Eight of nine reconnection events studied occur at SKR phases where the SKR power would be expected to be rising with time. Thus, while the recurrence rate of substorm-like events at Saturn is likely much longer than the Planetary Rotation timescale, the events are favored to occur at a particular phase of the Rotation. We show three examples in each of which the SKR spectrum extends to lower frequencies than usual. This can be interpreted as an expansion of the auroral particle acceleration region to higher altitudes along magnetic field lines as a direct consequence of an increase in the magnetosphere-ionosphere current density driven by substorm-like events. We then conduct a survey of such low-frequency extensions during the equatorial orbits of 2005–2006 and place some constraints on visibility of these radio emissions.

  • phase relation of oscillations near the Planetary period of saturn s auroral oval and the equatorial magnetospheric magnetic field
    Web Science, 2009
    Co-Authors: G Provan, S W H Cowley, J D Nichols
    Abstract:

    [1] Previous analyses of Hubble Space Telescope (HST) images of Saturn's southern auroras obtained during two campaigns, in January 2007 and February 2008, have revealed that the auroral oval oscillates at a period close to the Planetary Rotation period, with its center describing an elongated ellipse of semimajor axis ∼2° colatitude aligned along the prenoon to premidnight direction. Previous analyses of Cassini magnetic field data from Saturn's near-equatorial quasi-dipolar magnetosphere have also established the presence of a rotating pattern of magnetic field perturbations near the Planetary period, a phase model which has been derived from data over the interval from mid-2004 to the end of 2007, whose extrapolation is verified here for use during the February 2008 HST campaign. In this paper we compare the phases of these oscillatory phenomena and show that the southern oval displacement was directed approximately opposite to the rotating equatorial perturbation field during both HST campaign intervals. We also examine the relation of the southern oval oscillations to the periodic power modulations in Saturn kilometric radiation (SKR) and show that the southern oval was displaced sunward at SKR maxima. It is suggested that the oval displacements are related to magnetospheric field line distortions associated with the rotating magnetic field perturbations, this picture also being consistent with recently reported periodic tilting of the equatorial plasma sheet. We note, however, that this picture provides no immediate explanation for the significantly elliptical nature of the observed oval motion.

  • cassini observations of Planetary period magnetic field oscillations in saturn s magnetosphere doppler shifts and phase motion
    Geophysical Research Letters, 2006
    Co-Authors: S W H Cowley, M K Dougherty, E J Bunce, D M Wright, A C Carter, G Giampieri, J D Nichols, T R Robinson
    Abstract:

    [1] Cassini magnetic field observations show that few-nT oscillations near the Planetary Rotation period, first observed in Pioneer-11 and Voyager-1 and -2 fly-by data, are essentially ubiquitous in Saturn's magnetosphere, though their character differs between the quasi-dipolar ring current region and the dawn tail. Examination of data from the ring-current region shows, however, that the observed oscillation period is not fixed at the Planetary period, but has smaller values on the inbound pass of the spacecraft, increasing to larger values at and beyond periapsis. These variations are shown to be consistent with the Doppler shifts due to spacecraft motion expected in a model in which the wave phase fronts rotate with the planet, and radiate outward at a speed comparable with the equatorial Alfven speed.

Tapio Schneider - One of the best experts on this subject based on the ideXlab platform.

  • atmospheric dynamics of earth like tidally locked aquaplanets
    Journal of Advances in Modeling Earth Systems, 2010
    Co-Authors: Timothy M Merlis, Tapio Schneider
    Abstract:

    We present simulations of atmospheres of Earth-like aquaplanets that are tidally locked to their star, that is, planets whose orbital period is equal to the Rotation period about their spin axis, so that one side always faces the star and the other side is always dark. Such simulations are of interest in the study of tidally locked terrestrial exoplanets and as illustrations of how Planetary Rotation and the insolation distribution shape climate. As extreme cases illustrating the effects of slow and rapid Rotation, we consider planets with Rotation periods equal to one current Earth year and one current Earth day. The dynamics responsible for the surface climate (e.g., winds, temperature, precipitation) and the general circulation of the atmosphere are discussed in light of existing theories of atmospheric circulations. For example, as expected from the increasing importance of Coriolis accelerations relative to inertial accelerations as the Rotation rate increases, the winds are approximately isotropic and divergent at leading order in the slowly rotating atmosphere but are predominantly zonal and Rotational in the rapidly rotating atmosphere. Free-atmospheric horizontal temperature variations in the slowly rotating atmosphere are generally weaker than in the rapidly rotating atmosphere. Interestingly, the surface temperature on the night side of the planets does not fall below ∼240 K in either the rapidly or slowly rotating atmosphere; that is, heat transport from the day side to the night side of the planets efficiently reduces temperature contrasts in either case. Rotational waves and eddies shape the distribution of winds, temperature, and precipitation in the rapidly rotating atmosphere; in the slowly rotating atmosphere, these distributions are controlled by simpler divergent circulations. Both the slowly and rapidly rotating atmospheres exhibit equatorial superRotation. Systematic variation of the Planetary Rotation rate shows that the equatorial superRotation varies non-monotonically with Rotation rate, whereas the surface temperature contrast between the day side and the night side does not vary strongly with changes in Rotation rate.

  • atmospheric dynamics of earth like tidally locked aquaplanets
    arXiv: Earth and Planetary Astrophysics, 2010
    Co-Authors: Timothy M Merlis, Tapio Schneider
    Abstract:

    We present simulations of atmospheres of Earth-like aquaplanets that are tidally locked to their star, that is, planets whose orbital period is equal to the Rotation period about their spin axis, so that one side always faces the star and the other side is always dark. As extreme cases illustrating the effects of slow and rapid Rotation, we consider planets with Rotation periods equal to one current Earth year and one current Earth day. The dynamics responsible for the surface climate (e.g., winds, temperature, precipitation) and the general circulation of the atmosphere are discussed in light of existing theories of atmospheric circulations. For example, as expected from the increasing importance of Coriolis accelerations relative to inertial accelerations as the Rotation rate increases, the winds are approximately isotropic and divergent at leading order in the slowly rotating atmosphere but are predominantly zonal and Rotational in the rapidly rotating atmosphere. Free-atmospheric horizontal temperature variations in the slowly rotating atmosphere are generally weaker than in the rapidly rotating atmosphere. Interestingly, the surface temperature on the night side of the planets does not fall below ~240 K in either the rapidly or slowly rotating atmosphere; that is, heat transport from the day side to the night side of the planets efficiently reduces temperature contrasts in either case. Rotational waves shape the distribution of winds, temperature, and precipitation in the rapidly rotating atmosphere; in the slowly rotating atmosphere, these distributions are controlled by simpler divergent circulations. The results are of interest in the study of tidally locked terrestrial exoplanets and as illustrations of how Planetary Rotation and the insolation distribution shape climate.