Polar cap potentials and the auroral electrojet indices

Weimer, D. R.; Maynard, N. C.; Burke, William J.; Liebrecht, C.

doi:10.1016/0032-0633(90)90028-o

Cited by 49 publications

(32 citation statements)

References 33 publications

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“…For the southward B Z cases, the average of IMF | B Z | is about 10% higher during equinox, which might be expected according to the theory of Russell and McPherron [1973]. The histogram of the AE index does suggest higher geomagnetic activity during these conditions, and a positive correlation between the AE index and the cross‐polar cap potential had been established by Reiff et al [1981] and Weimer et al [1990] from satellite measurements; by Weimer et al [1990] using the VEFI measurements; by Ahn et al [1984, 1992] for equinox and solstice events, using the Kamide, Richmond, and Matsushita (KRM) algorithm [ Kamide et al , 1981]; and by Richmond et al [1990], Cooper et al [1995], and Lu et al [1998] for three different solstice events, using the AMIE procedure.…”

Section: Discussionmentioning

confidence: 57%

High‐latitude ionospheric electric field variability and electric potential derived from DE‐2 plasma drift measurements: Dependence on IMF and dipole tilt

2003

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[1] In this study the characteristics of electric field variability are investigated by using the sample standard deviations estimated from plasma drift measurements obtained during the Dynamics Explorer 2 (DE-2) mission. The spatial distribution of the standard deviation over the area poleward of 45°magnetic latitude and its climatological behavior with respect to the magnitude and orientation of the interplanetary magnetic field (IMF) and the dipole tilt angle (season) are examined. In comparison with past studies based on ground-based measurements and with results from a data assimilation model, this study quantifies the electric field variability with more complete spatial coverage and with more extensive climatological information and therefore is of importance to the problem of the global Joule heating estimation in thermospheric general circulation modeling. In general, the magnitude of the standard deviation exceeds the strength of the mean electric field in most of the polar area, especially under northward IMF conditions. In contrast to the climatological electric field, whose magnitude tends to be most intense in the polar cap, the standard deviation generally intensifies in the vicinity of the convection reversal and the cusp. Under most IMF clock angles the area of the largest electric field variability lies near the cusp; under the southward B Z condition the area extends toward the potential maximum on the dawn side and toward the region of strong sunward convection in the afternoon, while under the positive B Y condition the area extends poleward of the potential maximum on the dawn side. The analysis reveals that electric field variability varies with magnetic latitude, magnetic local time, IMF, and season in a manner distinct from that of the climatological electric field. This indicates that empirical models and data assimilation models designed to reproduce the average electric potential or the average electric fields correctly are not necessarily well-suited to represent the squared electric fields or the electric field variability correctly.

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Section: Discussionmentioning

confidence: 57%

High‐latitude ionospheric electric field variability and electric potential derived from DE‐2 plasma drift measurements: Dependence on IMF and dipole tilt

2003

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“…On the other hand in winter the UT eect was pronounced. The summer variation in the AE index might be aected by a large increase in the conductivity in the auroral region when most of the auroral zone is in the day time sector as pointed out by Berthelier (1976) and Weimer et al (1990). This would obscure the UT variations due to a change in the SunEarth magnetic con®guration.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Longitudinal (UT) effect in the onset of auroral disturbances over two solar cycles as deduced from the AE-index

Hajkowicz

1998

Ann Geophysicae

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Abstract. Statistical study on the universal time variations in the mean hourly auroral electrojet index (AEindex) has been undertaken for a 21 y period over two solar cycles (1957±1968 and 1978±1986). The analysis, applied to isolated auroral substorm onsets (inferred from rapid variations in the AE-index) and to the bulk of the AE data, indicates that the maximum in auroral activity is largely con®ned to 09±18 UT, with a distinct minimum at 03±06 UT. The diurnal eect was clearly present throughout all seasons in the ®rst cycle but was mainly limited to northern winter in the second cycle. Severe storms (AE > 1000 nT) tended to occur between 9±18 UT irrespective of the seasons whereas all larger magnetic disturbances (AE > 500 nT) tended to occur in this time interval mostly in winter. On the whole the diurnal trend was strong in winter, intermediate at equinox and weak in summer. The implication of this study is that Eastern Siberia, Japan and Australia are mostly at night, during the period of maximum auroral activity whereas Europe and Eastern America are then mostly at daytime. The minimum of auroral activity coincides with near-midnight conditions in Eastern America. It appears that the diurnal UT distribution in the AE-index re¯ects a diurnal change between interplanetary magnetic ®eld orientation and the Earth's magnetic dipole inclination.

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“…Therefore, the temporal variation of the total hemispheric Joule heating most probably follows the temporal variation of the global electric field, and consequently the polar cap potential. The polar cap potential difference has been found to be linearly proportional to the AE index (Ahn et al, 1984;Weimer et al, 1990), and therefore the temporal variation of the polar cap potential should follow that of the AE index (Fig. 2).…”

Section: Discussionmentioning

confidence: 99%

Assessment of ionospheric Joule heating by GUMICS-4 MHD simulation, AMIE, and satellite-based statistics: towards a synthesis

et al. 2005

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Abstract.We investigate the Northern Hemisphere Joule heating from several observational and computational sources with the purpose of calibrating a previously identified functional dependence between solar wind parameters and ionospheric total energy consumption computed from a global magnetohydrodynamic (MHD) simulation (Grand Unified Magnetosphere Ionosphere Coupling Simulation, GUMICS-4). In this paper, the calibration focuses on determining the amount and temporal characteristics of Northern Hemisphere Joule heating. Joule heating during a substorm is estimated from global observations, including electric fields provided by Super Dual Auroral Network (Super-DARN) and Pedersen conductances given by the ultraviolet (UV) and X-ray imagers on board the Polar satellite. Furthermore, Joule heating is assessed from several activity index proxies, large statistical surveys, assimilative data methods (AMIE), and the global MHD simulation GUMICS-4. We show that the temporal and spatial variation of the Joule heating computed from the GUMICS-4 simulation is consistent with observational and statistical methods. However, the different observational methods do not give a consistent estimate for the magnitude of the global Joule heating. We suggest that multiplying the GUMICS-4 total Joule heating by a factor of 10 approximates the observed Joule heating reasonably well. The lesser amount of Joule heating in GUMICS-4 is essentially caused by weaker Region 2 currents and polar cap potentials. We also show by theoretical arguments that multiplying independent measurements of averaged electric fields and Pedersen conductances yields an overestimation of Joule heating.Correspondence to: M. Palmroth (Minna.Palmroth@fmi.fi)

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Polar cap potentials and the auroral electrojet indices

Cited by 49 publications

References 33 publications

High‐latitude ionospheric electric field variability and electric potential derived from DE‐2 plasma drift measurements: Dependence on IMF and dipole tilt

High‐latitude ionospheric electric field variability and electric potential derived from DE‐2 plasma drift measurements: Dependence on IMF and dipole tilt

Longitudinal (UT) effect in the onset of auroral disturbances over two solar cycles as deduced from the AE-index

Assessment of ionospheric Joule heating by GUMICS-4 MHD simulation, AMIE, and satellite-based statistics: towards a synthesis

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