Polar cap convection patterns inferred from EISCAT observations

Peymirat, C.; Fontaine, Dominique

doi:10.1007/s00585-997-0403-9

Cited by 15 publications

(7 citation statements)

References 26 publications

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“…Thus this table allows us to compare the cross‐polar potentials obtained from different data sources and utilized different techniques. We would include in Table 1 a number of other models for comparison [e.g., Heelis et al , 1982; Foster , 1983; Heppner and Maynard , 1987; Holt et al , 1987; Hairston and Heelis , 1990; Peymirat and Fontaine , 1997], but these models either are not organized by the IMF clock angle or are not clearly organized by the IMF magnitude.…”

Section: Discussionmentioning

confidence: 99%

High‐latitude ionospheric convection models derived from Defense Meteorological Satellite Program ion drift observations and parameterized by the interplanetary magnetic field strength and direction

2002

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[1] A series of new high-latitude ionospheric convection models have been constructed using Defense Meteorological Satellite Program (DMSP) thermal ion drift measurements. The models are obtained by sorting cross polar cap electrostatic potentials into magnetic latitude/magnetic local time bins. A regression analysis of the potentials in each bin is then implemented for establishing the relationships to the interplanetary magnetic field (IMF) for three seasons: summer, winter, and equinox. A linear modeling formula for the ionospheric electrodynamics (LIMIE) yields a convection response to the average solar wind (i.e., the ''quasi-viscous'' interaction) and to changes in the IMF B y , B z 0, and B z > 0 components. The modeled convection is a superposition of the first two parameters with either the IMF B z 0 or the B z > 0 component. A global model is created by fitting the regression analysis results to a spherical harmonic function. The resulting DMSP-based ionospheric convection model (DICM) is fully parameterized by the IMF strength and direction. With this model, ionospheric convection patterns can be generated for any IMF configuration during quiet to moderate geomagnetic conditions. We compare the DICM model with other available high-latitude convection patterns organized by the IMF. The new elements in DICM are its quasi-viscous and separate IMF-dependent terms for both the northern and southern polar regions, which are not explicitly found in other ionospheric convection studies. The DICM's seasonal dependence and interhemispheric symmetry/asymmetry features show that the summer cross-polar potentials are 10-15% smaller than the winter potentials. The latter is in agreement with the seasonal dependence of field-aligned currents and with the voltage-current relationship required for the proper magnetosphereionosphere coupling.

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Section: Discussionmentioning

confidence: 99%

High‐latitude ionospheric convection models derived from Defense Meteorological Satellite Program ion drift observations and parameterized by the interplanetary magnetic field strength and direction

2002

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“…Note, however, that for quiet magnetic activity, the polar cap boundary is usually located at magnetic latitudes higher than the 71.97 we take at the beginning of the simulations. For instance, for quiet steady state conditions, Hairston and Heelis [1990], Peymirat and Fontaine [1997], and Foster et al [1986] showed that the polar cap is located between 73°a nd 77°invariant latitude for potential drops between 30 and 38 kV. However, because our magnetosphere is a simple dipole, it cannot reasonably approximate realistic magnetic field mapping for lines at such high ionospheric magnetic latitudes.…”

Section: Polar Cap Potentialmentioning

confidence: 95%

Long‐lasting disturbances in the equatorial ionospheric electric field simulated with a coupled magnetosphere‐ionosphere‐thermosphere model

2003

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The Magnetosphere‐Thermosphere‐Ionosphere‐Electrodynamics General Circulation model of Peymirat et al. [1998] is used to investigate ionospheric‐wind‐dynamo influences on low‐latitude ionospheric electric fields during and after a magnetic storm. Simulations are performed with time‐varying polar cap electric potentials and an expanding and contracting polar cap boundary. Three influences on equatorial electric fields can be of comparable importance: (1) global winds driven by solar heating; (2) direct penetration of polar cap electric fields to the equator that are partially shielded by the effects of Region‐2 field‐aligned currents; and (3) disturbance winds driven by high‐latitude heating and ion‐drag acceleration. The first two influences tend to have similar magnetic local time (MLT) variations in a steady state, while the disturbance‐wind influence tends to have the opposite MLT variations. The nighttime disturbance winds at upper midlatitudes that affect the global ionospheric wind dynamo are predominantly westward after the simulated magnetic storm. The nighttime winds drive an equatorward dynamo current that tends to charge the low‐latitude ionosphere positively around midnight, which can lead to reductions or reversals of the normal equatorial night‐side east‐west electric fields. The simulations partly support the theories of the so‐called “disturbance dynamo” [Blanc and Richmond, 1980] and “fossil wind” [Spiro et al., 1988], both of which predict long‐lasting disturbances in the equatorial eastward electric field associated with magnetic storms. However, the simulations do not support the element of fossil wind theory that links the disturbance‐wind influence on equatorial electric fields to polar cap contraction following the storm. The simulations show a stronger wind‐produced enhancement of steady state shielding than predicted by the model of Forbes and Harel [1989], due to the fact that the disturbance winds extend well equatorward of the Region‐2 currents.

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“…The SWM voltage‐generator cases in section 3 use the potential model of Heelis et al [1982], with a sinusoidal shape of the potential along the PCB that Boyle et al [1997] showed to be adequate for southward steady states of the interplanetary magnetic field (IMF) and with a polar cap potential drop of either 30 kV or 70 kV. Although the polar cap radius of 18.0° is consistent with a polar cap potential drop of 70 kV, it overestimates the size of the polar cap for a potential drop of 30 kV, where a radius of ∼15° is expected [ Peymirat and Fontaine , 1997]. However, keeping the PCB fixed allows us to distinguish the effects associated with variations of the polar potential drop from those related to a displaced PCB.…”

Section: Model and Simulation Conditionsmentioning

confidence: 99%

Neutral wind influence on the electrodynamic coupling between the ionosphere and the magnetosphere

2002

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[1] The influence of the ionospheric wind dynamo on the steady state electrodynamic interaction between the ionosphere and the inner magnetosphere is evaluated with the Magnetosphere-Thermosphere-Ionosphere Electrodynamics General Circulation Model (MTIE-GCM) of Peymirat et al. [1998]. Two types of interaction between the solar wind -magnetosphere (SWM) dynamo and the ionospheric dynamo are considered: either the SWM dynamo is a voltage generator imposing a fixed electric potential in the polar cap or it is a hybrid current/voltage generator such that the electric potential in the polar cap results from the combined action of the SWM and ionospheric dynamos. The following results are found. (1) The dynamo effect of winds that are accelerated by the high-latitude ion convection increases the meridional electric field in the auroral zone but reduces the potential variation around the Auroral Zone Equatorial boundary (AZEQ) and the plasma pressure in the nightside magnetosphere close to the Earth, corresponding to an enhancement of the shielding effect produced by Region 2 field-aligned currents. The magnitudes of the wind-induced effects are on the order of 10% for the shielding potential and 20% for the plasma pressure reduction. (2) The wind-induced reduction of magnetospheric plasma pressure near the Earth is $4 times larger for a doubling of the plasma source density in the tail. (3) The relative influence of winds on shielding is similar for polar cap potential drops of 30 kV and 70 kV. (4) When the wind is allowed to influence the polar cap potential, it increases the potential drop along the polar cap boundary by $10% but does not modify the net influence on the shielding potential along AZEQ. (5) The influence of the neutral winds set up by the high-latitude convection is rest ricted to the aurora l zone.I NDEX TERMS: 2736

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Polar cap convection patterns inferred from EISCAT observations

Cited by 15 publications

References 26 publications

High‐latitude ionospheric convection models derived from Defense Meteorological Satellite Program ion drift observations and parameterized by the interplanetary magnetic field strength and direction

High‐latitude ionospheric convection models derived from Defense Meteorological Satellite Program ion drift observations and parameterized by the interplanetary magnetic field strength and direction

Long‐lasting disturbances in the equatorial ionospheric electric field simulated with a coupled magnetosphere‐ionosphere‐thermosphere model

Neutral wind influence on the electrodynamic coupling between the ionosphere and the magnetosphere

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