Polar heating in Saturn's thermosphere

Smith, C.; Aylward, A. D.; Miller, Steve; Müller‐Wodarg, I. C. F.

doi:10.5194/angeo-23-2465-2005

Cited by 25 publications

(29 citation statements)

References 25 publications

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“…This is consistent with recent results for Saturn (Smith et al, 2005b;Müller-Wodarg et al, 2006;Smith et al, 2007). Even when we added enough high latitude heating to raise the polar temperature to 1500 K -slightly in excess of the observations -the equatorial temperature was still low, in the region of 400 K. Figure 16 shows a comparison between temperature profiles predicted by our model and the Galileo probe temperature profile (Seiff et al, 1998).…”

Section: Thermospheresupporting

confidence: 79%

“…Similar high temperatures are present in Saturn's thermosphere, and recent studies have attempted to explain these measurements by the redistribution of high latitude heating. Smith et al (2005b) found that an arbitrary high latitude source of thermal energy did generate sufficient redistributive winds to reproduce the observed temperatures, but the more sophisticated calculations of Smith et al (2007) showed that when high-latitude energy inputs of Joule heating and ion drag were included, poleward meridional winds were generated that cooled, rather than heated, low latitudes.…”

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confidence: 99%

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Coupled rotational dynamics of Jupiter's thermosphere and magnetosphere

2009

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Abstract.We describe an axisymmetric model of the coupled rotational dynamics of the thermosphere and magnetosphere of Jupiter that incorporates self-consistent physical descriptions of angular momentum transfer in both systems. The thermospheric component of the model is a numerical general circulation model. The middle magnetosphere is described by a simple physical model of angular momentum transfer that incorporates self-consistently the effects of variations in the ionospheric conductivity. The outer magnetosphere is described by a model that assumes the existence of a Dungey cycle type interaction with the solar wind, producing at the planet a largely stagnant plasma flow poleward of the main auroral oval. We neglect any decoupling between the plasma flows in the magnetosphere and ionosphere due to the formation of parallel electric fields in the magnetosphere. The model shows that the principle mechanism by which angular momentum is supplied to the polar thermosphere is meridional advection and that mean-field Joule heating and ion drag at high latitudes are not responsible for the high thermospheric temperatures at low latitudes on Jupiter. The rotational dynamics of the magnetosphere at radial distances beyond ∼30 R J in the equatorial plane are qualitatively unaffected by including the detailed dynamics of the thermosphere, but within this radial distance the rotation of the magnetosphere is very sensitive to the rotation velocity of the thermosphere and the value of the Pedersen conductivity. In particular, the thermosphere connected to the inner magnetosphere is found to super-corotate, such that true Pedersen conductivities smaller than previously predicted are required to enforce the observed rotation of the magnetosphere within ∼30 R J . We find that increasing the Joule heating at high latitudes by adding a component due to rapidly fluctuating electric fields is unable to explain the Correspondence to: C. G. A. Smith (cgasmith@gmail.com) high equatorial temperatures. Adding a component of Joule heating due to fluctuations at low latitudes is able to explain the high equatorial temperatures, but the thermospheric wind systems generated by this heating cause super-corotation of the inner magnetosphere in contradiction to the observations. We conclude that the coupled model is a particularly useful tool for study of the thermosphere as it allows us to constrain the plausibility of predicted thermospheric structures using existing observations of the magnetosphere.

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Section: Thermospheresupporting

confidence: 79%

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confidence: 99%

Coupled rotational dynamics of Jupiter's thermosphere and magnetosphere

2009

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“…In turn, this would correspond to a cooling rate of 7.8 × 10 12 W for the whole column above the homopause, or 3.2 × 10 12 W for the column above the main H + 3 emission layer. This is a highly significant rate, and corresponds to the kind of heating rates produced in Saturn's polar upper atmosphere by Joule heating and ion drag [24].…”

Section: Cassini Measurements Of the Aurora Of Saturnmentioning

confidence: 93%

Temperature changes and energy inputs in giant planet atmospheres: what we are learning from H ₃ ⁺

Stallard

Melin

Miller

et al. 2012

Phil. Trans. R. Soc. A.

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Since its discovery at Jupiter in 1988, emission from H + 3 has been used as a valuable diagnostic tool in our understanding of the upper atmospheres of the giant planets. One of the lasting questions we have about the giant planets is why the measured upper atmosphere temperatures are always consistently hotter than the temperatures expected from solar heating alone. Here, we describe how H at Saturn and the first profile of H + 3 emission at Uranus not significantly distorted by the effects of the Earth's atmosphere. We also review past observations of variations in temperature measured at Uranus and Jupiter over a wide variety of time scales. To this, we add new observations of temperature changes at Saturn, using observations by Cassini. We conclude that the causes of the significant level of thermal variability observed over all three planets is not only an important question in itself, but that explaining these variations could be the key to answering the more general question of why giant planet upper atmospheres are so hot.

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“…The above considerations enable more detailed vertical profiles of the thermosphere to be developed. These are shown below for Jupiter ( Figure 3; Grodent et al, 2001) and for Saturn (Figure 4;Smith et al, 2004). They show that, except at the very bottom of the thermosphere, where hydrocarbon molecules still have some abundance, the atmosphere is composed mainly of molecular and atomic hydrogen, with helium as a minor species.…”

Section: Basic Thermospheric Parametersmentioning

confidence: 94%

Giant Planet Ionospheres and Thermospheres: The Importance of Ion-Neutral Coupling

2005

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Planetary upper atmospheres -coexisting thermospheres and ionospheres -form an important boundary between the planet itself and interplanetary space. The solar wind and radiation from the Sun may react with the upper atmosphere directly, as in the case of Venus. If the planet has a magnetic field, however, such interactions are mediated by the magnetosphere, as in the case of the Earth. All of the Solar System's giant planets have magnetic fields of various strengths, and interactions with their space environments are thus mediated by their respective magnetospheres. This article concentrates on the consequences of magnetosphere-atmosphere interactions for the physical conditions of the thermosphere and ionosphere. In particular, we wish to highlight important new considerations concerning the energy balance in the upper atmosphere of Jupiter and Saturn, and the role that coupling between the ionosphere and thermosphere may play in establishing and regulating energy flows and temperatures there. This article also compares the auroral activity of Earth, Jupiter, Saturn and Uranus. The Earth's behaviour is controlled, externally, by the solar wind. But Jupiter's is determined by the co-rotation or otherwise of the equatorial plasmasheet, which is internal to the planet's magnetosphere. Despite being rapid rotators, like Jupiter, Saturn and Uranus appear to have auroral emissions that are mainly under solar (wind) control. For Jupiter and Saturn, it is shown that Joule heating and "frictional" effects, due to ion-neutral coupling can produce large amounts of energy that may account for their high exospheric temperatures.

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Polar heating in Saturn's thermosphere

Cited by 25 publications

References 25 publications

Coupled rotational dynamics of Jupiter's thermosphere and magnetosphere

Coupled rotational dynamics of Jupiter's thermosphere and magnetosphere

Temperature changes and energy inputs in giant planet atmospheres: what we are learning from H ₃ ⁺

Giant Planet Ionospheres and Thermospheres: The Importance of Ion-Neutral Coupling

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Polar heating in Saturn's thermosphere

Cited by 25 publications

References 25 publications

Coupled rotational dynamics of Jupiter's thermosphere and magnetosphere

Coupled rotational dynamics of Jupiter's thermosphere and magnetosphere

Temperature changes and energy inputs in giant planet atmospheres: what we are learning from H 3 +

Giant Planet Ionospheres and Thermospheres: The Importance of Ion-Neutral Coupling

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Product

Resources

About

Temperature changes and energy inputs in giant planet atmospheres: what we are learning from H ₃ ⁺