Quiet-time pattern of auroral arcs for different directions of the interplanetary magnetic field in the Y-Z plane.

Using criticaI frequencies, f0F2 from the Uppsala, Lannion and Dourbes ionosonde stations, the possible effects of the orientation of the IMF on mid-latitude ionosphere are further investigated. For this purpose, the regular diurnal, seasonal and solar cycle variations in the f0F2 data were removed by subtracting the mean of f0F2 for the same UT on all the magnetically quiet days (Ap< 6) within 15 days around the IMF Bz turnings. This yields the deviation from the average quiet-time value ?f0F2. The data are sorted according to the polarity of the IMF Bz and the effects of the southward turnings are discussed. Hapgood et al. (1991), Tulunay et al. (1991), Tulunay and Rahman (1992) investigated the possible effects of the IMF on mid-latitude ionosphere by employing the Slough and Argentine Islands f0F2 data. In order to facilitate a comparison the same method of analysis is being adopted again. However, in the present work the southward polarity changes in IMF Bz with no consideration of the IMF sector structure were considered only.

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Filamentary field-aligned currents at the polar cap region during northward interplanetary magnetic field derived with the Swarm constellation

Annales Geophysicae ◽

10.5194/angeo-34-901-2016 ◽

2016 ◽

Vol 34 (10) ◽

pp. 901-915 ◽

Cited By ~ 12

Author(s):

Hermann Lühr ◽

Tao Huang ◽

Simon Wing ◽

Guram Kervalishvili ◽

Jan Rauberg ◽

...

Keyword(s):

Magnetic Field ◽

Interplanetary Magnetic Field ◽

Initial Study ◽

Auroral Oval ◽

Closed Field ◽

Defense Meteorological Satellite Program ◽

Field Lines ◽

Auroral Arcs ◽

First Time ◽

Meteorological Satellite

Abstract. ESA's Swarm constellation mission makes it possible for the first time to determine field-aligned currents (FACs) in the ionosphere uniquely. In particular at high latitudes, the dual-satellite approach can reliably detect some FAC structures which are missed by the traditional single-satellite technique. These FAC events occur preferentially poleward of the auroral oval and during times of northward interplanetary magnetic field (IMF) orientation. Most events appear on the nightside. They are not related to the typical FAC structures poleward of the cusp, commonly termed NBZ. Simultaneously observed precipitating particle spectrograms and auroral images from Defense Meteorological Satellite Program (DMSP) satellites are consistent with the detected FACs and indicate that they occur on closed field lines mostly adjacent to the auroral oval. We suggest that the FACs are associated with Sun-aligned filamentary auroral arcs. Here we introduce in an initial study features of the high-latitude FAC structures which have been observed during the early phase of the Swarm mission. A more systematic survey over longer times is required to fully characterize the so far undetected field aligned currents.

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The response of the quiet-time auroral configuration to short- and long-term interplanetary magnetic field variations

Canadian Journal of Physics ◽

10.1139/p91-161 ◽

1991 ◽

Vol 69 (8-9) ◽

pp. 1040-1046 ◽

Cited By ~ 3

Author(s):

J. S. Murphree ◽

L. L. Cogger ◽

R. D. Elphinstone ◽

D. Hearn

Keyword(s):

Magnetic Field ◽

Interplanetary Magnetic Field ◽

Polar Angle ◽

Wave Interaction ◽

Energy Coupling ◽

Quiet Time ◽

Short And Long Term ◽

Standard Energy ◽

Magnetic Field Variations

Observations from the IMP-8 satellite of the interplanetary magnetic field (IMF) are compared with areas of the polar region bounded by the aurora as observed by the Viking spacecraft during quiet-time conditions (IMF Bz northward). A variety of energy-coupling functions are investigated and it is determined that the auroral distribution can be best described by the inclusion of azimuthal terms in addition to standard energy-coupling functions. The auroral distributions for Bz northward support antiparallel merging as a mechanism whereby energy is transferred to the magnetosphere from the solar wind. As well, however, when the polar angle is small the region bounded by the auroras expands and may be controlled more by wave interaction at the magnetopause. Observations by the Viking spacecraft indicate a dominance of dusk sector polar arcs in the spring time and dawn sector arcs in the fall (post equinox). Two alternative mechanisms can explain the observations. One involves the ordering of the IMF in a solar equatorial coordinate system while the other involves the Sun's polarity and the traversal of the Earth's orbit through different heliographic latitudes. A test is proposed whereby the two hypotheses can be investigated during the next solar cycle.

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