Universal-time control of the low-energy electron fluxes in the polar regions

Maehlum, B.N.

doi:10.1029/ja073i011p03459

Cited by 57 publications

(12 citation statements)

References 21 publications

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“…Another suggested explanation is based on soft electron precipitation [Duncan, 1962[Duncan, , 1969Pike, 1970], which could vary with universal time. Such a fluctuation in the high-latitude limit of precipitation has been reported by Maehlum [1968] for the north polar region with a maximum at 1800-2000 UT. The suggested explanation for this latter phenomenon is the daily change in orientation of the magnetic poles with respect to the earth-sun line.…”

supporting

confidence: 69%

Longitudinal variations of thermospheric composition indicating magnetic control of polar heat input

Hedin¹,

Reber²

1972

J. Geophys. Res.

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Measurements of neutral N2, O, and He densities from Ogo 6 over the south polar region during magnetically quiet periods in late August and early September 1969 indicate that N2 densities, when they are extrapolated to a common altitude, maximize at about 0800 UT near 70° invariant latitude. The density of He has a minimum at this time, and the density of O has a slight maximum. It is proposed that these phenomena are the result of cyclic variations in soft electron precipitation, which heats the thermosphere either directly or through enhanced Joule heating. This heat energy would increase the gas temperature, the increase in the gas temperature leading to the N2 increase, and would vary the composition by generation of a wind system.

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supporting

confidence: 69%

Longitudinal variations of thermospheric composition indicating magnetic control of polar heat input

Hedin¹,

Reber²

1972

J. Geophys. Res.

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“…They suggested that the UT eect is more fundamental and re¯ects an interaction between interplanetary magnetic ®eld orientation and the Earth's magnetic dipole inclination. A similar suggestion, regarding UT eects in auroral particle precipitation, was given by Maehlum (1968) who pointed out there are large UT variations during the day in the angle between the Earth's magnetic axis and the Sun-Earth line. The change in the orientation of the Earth's ®eld relative to the direction of the solar wind can cause`wagging' in the Earth's magnetotail and thus aect the longitudinal distribution of the particle precipitation.…”

Section: Conclusion and Discussionmentioning

confidence: 80%

“…An early study of the longitudinal dependence in auroral particle precipitation was conducted by Loughnan (1961) who suggested that there is a marked longitudinal leakage of auroral particles from the trapped-radiation regions. An experimental particle observation project from a satellite has revealed a large universal-time variation in low-energy electron¯uxes (Maehlum, 1968). He associated these variations with the diurnal changes in the tilt of the Earth's geomagnetic axis relative to the solar wind direction.…”

Section: Introductionmentioning

confidence: 99%

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

Hajkowicz

1998

Ann. Geophys.

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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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“…This region has been described as a 'soft' zone (Burch, 1968) or 'burst' zone (Hoffman, 1969). One of the important effects of the incidence of these low energy electrons on the earth's upper atmosphere is the production of ionization at F region levels and above (Maehlum, 1968;Burch, 1969; and Rees, 1969). The high latitude termination of the flux near the magnetic pole appeased to be responsible for the low 0 level of F region ionization and also of 6300 A intensity (Maehlum, 1969;Eather, 1969).…”

mentioning

confidence: 99%

Observations of the suprathermal electron flux and the electron temperature at high latitudes

Maier¹,

Rao²

1970

J. Geophys. Res.

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Observations of suprathermal electrons in the energy range of 5–200 ev were obtained with retarding potential analyzers on Explorer 31 in the altitude range of 1700–3000 km over the northern high latitudes during the winter of 1965–1966. There are three distinct zones that mainly consist of a steady flux of photoelectrons in the midlatitudes, a high and variable flux containing precipitated particles in the auroral latitudes, and a low flux over the polar region. Evidence is presented to show that the magnetic field lines are closed at least up to L = 7.7 for these particles. The boundaries of precipitation vary with local time and are somewhat different from those of the auroral oval. The ambient electron temperature appears to be dependent on the level of flux in the auroral and polar region.

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Universal-time control of the low-energy electron fluxes in the polar regions

Cited by 57 publications

References 21 publications

Longitudinal variations of thermospheric composition indicating magnetic control of polar heat input

Longitudinal variations of thermospheric composition indicating magnetic control of polar heat input

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

Observations of the suprathermal electron flux and the electron temperature at high latitudes

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