Mercury and Mars: The role of ionospheric conductivity in the acceleration of magnetospheric particles

Hill, T. W.; Dessler, A. J.; Wolf, R. A.

doi:10.1029/gl003i008p00429

Cited by 158 publications

(178 citation statements)

References 24 publications

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“…Such polar cap potential saturation is due to the nonlinear nature of the magnetosphere-ionosphere (M-I) coupling [Weimer et al, 1990]. Hill et al [1976] showed a current-voltage relationship, V = V M À I/AE 0, where V, V M , I, and AE 0 are the polar cap potential drop, the solar wind dynamo voltage, Birkeland current, and the critical conductivity (about 20 mho for typical solar wind parameters near the earth). It is independent of the Birkeland current.…”

Section: Discussionmentioning

confidence: 99%

Interplanetary magnetic field control of polar patch velocity

2003

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[1] Polar patch drift speed and direction have been investigated using oxygen 630 nm images recorded by an all-sky imager at Eureka (89°CGM), Canada over an extended period, January and December 1998. Statistical studies showed that (1) the interplanetary magnetic field (IMF, from the WIND satellite) B z component linearly controls the patch speed when B z is between À7.5 nT and 0 nT. The speed tends to saturate when B z is less than À7.5nT due to nonlinear coupling between the solar wind and the magnetosphere. The average patch speed of 600 m/s is in agreement with results from earlier studies; (2) The IMF B y or the IMF clock angle has a clear control of the patch drift direction as determined by the drift azimuth angle. When jB y j is less than 7.5nT, the drift azimuth angle is linearly and positively correlated with B y . For a large jB y j (>7.5 nT), the positive correlation is replaced by a negative correlated linear relation and the azimuth angle tends to turn towards 180 degrees; that is, the patches drift in an antisunward direction. These IMF B y effects can be qualitatively explained by the northern winter polar ionospheric convection models developed by Weimer [1995] and Hairston and Heelis [1990]. Results from our quantitative study on the IMF control of polar patch speed and drift direction provide constraints for the development of future polar ionospheric convection models.

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Section: Discussionmentioning

confidence: 99%

Interplanetary magnetic field control of polar patch velocity

2003

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“…[43] It is known that the electric potentials in the polar cap exhibit a saturation effect when the z-component of the IMF becomes increasingly negative [Hill et al, 1976;Siscoe et al, 2002]. This saturation curve has been investigated extensively through observations and theory, as reviewed by Shepherd [2007], and it may explain why the nonlinear correction is required.…”

Section: Derivation Of Dt C From Auroral Heatingmentioning

confidence: 99%

Predicting global average thermospheric temperature changes resulting from auroral heating

et al. 2011

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[1] The total Poynting flux flowing into both polar hemispheres as a function of time, computed with an empirical model, is compared with measurements of neutral densities in the thermosphere at two altitudes obtained from accelerometers on the CHAMP and GRACE satellites. The Jacchia-Bowman 2008 empirical thermospheric density model (JB2008) is used to facilitate the comparison. This model calculates a background level for the "global nighttime minimum exospheric temperature," T c , from solar indices. Corrections to this background level due to auroral heating, DT c , are presently computed from the Dst index. A proxy measurement of this temperature difference, DT c , is obtained by matching the CHAMP and GRACE density measurements with the JB2008 model. Through the use of a differential equation, the DT c correction can be predicted from IMF values. The resulting calculations correlate very well with the orbit-averaged measurements of DT c , and correlate better than the values derived from Dst. Results indicate that the thermosphere cools faster following time periods with greater ionospheric heating. The enhanced cooling is likely due to nitric oxide (NO) that is produced at a higher rate in proportion to the ionospheric heating, and this effect is simulated in the differential equations. As the DT c temperature correction from this model can be used as a direct substitute for the Dst-derived correction that is now used in JB200, it could be possible to predict DT c with greater accuracy and lead time.

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“…Hill et al (1976) suggested a' conductance value of 0.1 d o , which is not unreasonable based upon the lmar measiireniei& E this value were indeed appropriate, however, the high rate of joule heating in the regolith would severely limit the duration of the current flow as the available magnetospheric energy would be quickly dissipated. The analysis of the Mariner 10 magnetic field perturbations by Slavin et al (1997), however, suggest a longer duration FAC flow, and imply a higher conductivity closure path.…”

Section: How Will the Messnenger Observations Be Used To Discover Thementioning

confidence: 99%

“…These perturbations were first examined by Slavin et al (1997) who concluded that the spacecraft crossed three field-aligned current (FAC) sheets similar to those often observed at the Earth (Iijima and Potemra, 1978). The path by which these currents close is not known, but their existence may indicate that the conductivity of the regolith is greater than is usually assumed on the basis of analogy with the lunar surface (e.g., Hill et al, 1976). Indeed, arguments can be made for a wide range of regolith conductivities (Glassmeier, 1997;Janhunen and Kallio, 2004).…”

Section: Several Groups Have Estimated the Magnetic Moment Of Mercurymentioning

confidence: 99%

MESSENGER: Exploring Mercury’s Magnetosphere

et al. 2007

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Abstract. The MESSENGER mission to Mercury offers our first opportunity to explore this planet's miniature magnetosphere since the brief flybys of Mariner 10. Mercury's magnetosphere is unique in many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands off the solar wind only -1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic particles and, hence, no radiation belts. The characteristic time scales for wave propagation and convective transport are short and kinetic and fluid modes may be coupled. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury's interior may act to modify the solar wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects may be an important source of information on the state of Mercury's interior. In addition, Mercury's magnetosphere is the only one with its defining magnetic flux tubes rooted in a planetary regolith as opposed to an atmosphere with a conductive ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived, -1-2 min, substorm-like energetic particle events observed by Mariner 10 during its first traversal of Mercury's magnetic tail. Because of Mercury's proximity to the sun, 0.3 -0.5 AU, this magnetosphere experiences the most extreme driving forces in the solar system. All of these factors are expected to produce complicated interactions involving the exchange and re-cycling of neutrals and ions between the solar wind, magnetosphere, and regolith. The electrodynamics of Mercury's magnetosphere are expected to be equally complex, with strong forcing by the solar wind, magnetic reconnection at the magnetopause and in the tail, and the pick-up of planetary ions all driving field-aligned electric currents.However, these field-aligned currents do not close in an ionosphere, but in some other manner. In addition to the insights-into magnetospheric physics offered by study of the solar wind -Mercury system, quantitative specification of the "external" magnetic field generated by magnetospheric currents is necessary for accurate determination of the strength and multi-polar decomposition of Mercury's intrinsic magnetic field.MESSENGER'S highly capable instrumentation and broad orbital coverage will greatly advance our understanding of both the origin of Mercury's magnetic field and the acceleration of charged particles in small magnetospheres. In. this article, we review what is known about Mercury's magnetosphere and describe the MESSENGER science team's strategy for obtaining answers to the outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic, magnetosphere.2

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Mercury and Mars: The role of ionospheric conductivity in the acceleration of magnetospheric particles

Cited by 158 publications

References 24 publications

Interplanetary magnetic field control of polar patch velocity

Interplanetary magnetic field control of polar patch velocity

Predicting global average thermospheric temperature changes resulting from auroral heating

MESSENGER: Exploring Mercury’s Magnetosphere

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