Electric conductivities, electric fields and auroral particle energy injection rate in the auroral ionosphere and their empirical relations to the horizontal magnetic disturbances

Ahn, B.‐H.; Robinson, R. M.; Kamide, Y.; Akasofu, S.‐I.

doi:10.1016/0032-0633(83)90005-3

Cited by 92 publications

(47 citation statements)

References 26 publications

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“…Galand et al (2001) derive conductances from ion precipitation. The formulations given by Ahn et al (1983) and Ahn et al (1998) relate the Hall and Pedersen conductances to ground-based magnetometer measurements.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric control of the magnetosphere: conductance

2004

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Abstract.It is well known that the ionosphere plays a role in determining the global state of the magnetosphere. The ionosphere allows magnetospheric currents to close, thereby allowing magnetospheric convection to occur. The amount of current which can be carried through the ionosphere is mainly determined by the ionospheric conductivity. This paper starts to quantify the nonlinear relationship between the ionospheric conductivity and the global state of the magnetosphere. It is found that the steady-state magnetosphere acts neither as a current nor as a voltage generator; a uniform Hall conductance can influence the potential pattern at low latitudes, but not at high latitude; the EUV generated conductance forces the currents to close in the sunlight, while the potential is large on the nightside; the solar generated Hall conductances cause a large asymmetry between the dawn and dusk potential, which effects the pressure distribution in the magnetosphere; a uniform polar cap potential removes some of this asymmetry; the potential difference between solar minimum and maximum is ∼11%; and the auroral precipitation can be related to the local field-aligned current through an exponential function.

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Section: Introductionmentioning

confidence: 99%

Ionospheric control of the magnetosphere: conductance

2004

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“…Richmond et al, 1990). The conductivity distributions are estimated by modifying statistical models using correlations between ground magnetic signals and conductivity (Ahn et al, 1983), low Earth orbit particle precipitation data and UV auroral emission images when available. While the energy flux can be estimated from auroral UV images (Lummerzheim et al, 1997), the conductivities depend on the energy spectrum which must be estimated by comparing two bands in the UV (Germany et al, 1994).…”

Section: Discussionmentioning

confidence: 99%

High-latitude poynting flux from combined Iridium and SuperDARN data

et al. 2004

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Abstract. Field-aligned currents convey stress between the magnetosphere and ionosphere, and the associated low altitude magnetic and electric fields reflect the flow of electromagnetic energy to the polar ionosphere. We introduce a new technique to measure the global distribution of high latitude Poynting flux, S || , by combining electric field estimates from the Super Dual Auroral Radar Network (Super-DARN) with magnetic perturbations derived using magnetometer data from the Iridium satellite constellation. Spherical harmonic methods are used to merge the data sets and calculate S || for any magnetic local time (MLT) from the pole to 60 • magnetic latitude (MLAT). The effective spatial resolutions are 2 • MLAT, 2 h MLT, and the time resolution is about one hour due to the telemetry rate of the Iridium magnetometer data. The technique allows for the assessment of high-latitude net S || and its spatial distribution on one hour time scales with two key advantages: (1) it yields the net S || including the contribution of neutral winds; and (2) the results are obtained without recourse to estimates of ionosphere conductivity. We present two examples, 23 November 1999, 14:00-15:00 UT, and 11 March 2000, 16:00-17:00 UT, to test the accuracy of the technique and to illustrate the distributions of S || that it gives. Comparisons with in-situ S || estimates from DMSP satellites show agreement to a few mW/m 2 and in the locations of S || enhancements to within the technique's resolution. The total electromagnetic energy flux was 50 GW for these events. At auroral latitudes, S || tends to maximize in the morning and afternoon in regions less than 5 • in MLAT by two hours in MLT having S || =10 to 20 mW/m 2 and total power up to 10 GW. The power poleward of the Region 1 currents is about one-third of the total power, indicating significant energy flux over the polar cap.

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“…A similar study was performed by Fuller-Rowell and Evans (1987), who inferred height-integrated Hall and Pedersen conductivity values from electron and ion measurements detected between 0.3 and 20 keV, using particle precipitation data from the National Oceanic and Atmospheric Administration (NOAA) 6 and 7 satellites. A different approach was made by Ahn et al (1983); Hall and Pedersen conductances deduced from Chatanika radar data were compared with measurements of the horizontal component of the disturbed magnetic field (dH ) measured at College, Alaska. Ahn et al established empirical relationships between conductances and dH and these were used to compile global conductance models, on the basis of the global distribution of dH .…”

Section: Introductionmentioning

confidence: 99%

Instantaneous ionospheric global conductance maps during an isolated substorm

et al. 2002

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Abstract. Data from the Polar Ionospheric X-ray Imager (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to provide instantaneous global conductance maps. In this study, we focus on an isolated substorm event occurring on 31 July 1997. From the PIXIE and the UVI measurements, the energy spectrum of the precipitating electrons can be derived. By using a model of the upper atmosphere, the resulting conductivity values are generated. We present global maps of how the 5 min timeaveraged height-integrated Hall and Pedersen conductivities vary every 15 min during this isolated substorm. The method presented here enables us to study the time development of the conductivities, with a spatial resolution of ∼700 km. During the substorm, a single region of enhanced Hall conductance is observed. The Hall conductance maximum remains situated between latitudes 64 and 70 corrected geomagnetic (CGM) degrees and moves eastward. The strongest conductances are observed in the pre-midnight sector at the start of the substorm expansion. Toward the end of the substorm expansion and into the recovery phase, we find the Hall conductance maximum in the dawn region. We also observe that the Hall to Pedersen conductance ratio for the regions of maximum Hall conductance is increasing throughout the event, indicating a hardening of the electron spectrum. By combining PIXIE and UVI measurements with an assumed energy distribution, we can cover the whole electron energy range responsible for the conductances. Electrons with energies contributing most to the Pedersen conductance are well covered by UVI while PIXIE captures the high energetic component of the precipitating electrons affecting the Hall conductance. Most statistical conductance models have derived conductivities from electron precipitation data below approximately 30 keV. Since the intensity of the shortest UVI-wavelengths (LBHS) decreases significantly at higherCorrespondence to: A. Aksnes (arve.aksnes@fi.uib.no) electron energies, the UVI electron energy range is more or less comparable with the energy ranges of the statistical models. By calculating the conductivities from combined PIXIE and UVI measurements to compare with the conductivities from using UVI data only, we observe significant differences in the Hall conductance. The greatest differences are observed in the early evening and the late morning sector. We therefore suggest that the existing statistical models underestimate the Hall conductance.

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Electric conductivities, electric fields and auroral particle energy injection rate in the auroral ionosphere and their empirical relations to the horizontal magnetic disturbances

Cited by 92 publications

References 26 publications

Ionospheric control of the magnetosphere: conductance

Ionospheric control of the magnetosphere: conductance

High-latitude poynting flux from combined Iridium and SuperDARN data

Instantaneous ionospheric global conductance maps during an isolated substorm

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