The Freja Project

Lundin, R.; Haerendel, G.; Grahn, Sven

doi:10.1029/94gl01424

Cited by 45 publications

(19 citation statements)

References 6 publications

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“…Examples of such regions are the magnetopause, the plasma sheet boundary layer, and the auroral current regions. Recently, the Freja satellite [Lundin et al, 1994a] has observed what its team calls solitary kinetic Alfv6n wave structures (SKAWS). These waves are structured at the electron inertial length and could be directly related to the results reported here.…”

Section: C/o}pe (C Is the Speed Of Light And O}pe Is The Electron Pmentioning

confidence: 99%

Laboratory experiments on shear Alfvén waves and their relationship to space plasmas

Gekelman¹,

Vincena²,

Leneman³

et al. 1997

J. Geophys. Res.

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Section: C/o}pe (C Is the Speed Of Light And O}pe Is The Electron Pmentioning

confidence: 99%

Laboratory experiments on shear Alfvén waves and their relationship to space plasmas

Gekelman¹,

Vincena²,

Leneman³

et al. 1997

J. Geophys. Res.

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“…The joint Swedish and German satellite Freja (Lundin et al, 1994a,b) has a set of high resolution field and particle instruments, and an auroral imager, for studies of space plasma wave-particle interaction processes. Freja passes the auroral region in the Northern Hemisphere at an altitude of approximately 1700 km and the orbit has an inclination of about 63 • .…”

Section: Data Processingmentioning

confidence: 99%

The importance of solar illumination for discrete and diffuse aurora

et al. 2005

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Abstract. We present a comprehensive overview of the occurrence of discrete and diffuse aurora in the nightside Northern Hemisphere at invariant latitudes 55 • −75 • . Twenty-one months of Freja observations (1 January 1993 to 30 September 1994) from the Northern Hemisphere, obtained at ∼1700 km altitude, are included in this investigation. We investigate the importance of seasonal effects, solar illumination and geomagnetic activity for the auroral precipitation. The seasonal variations in the occurrence of discrete aurora are separated from the dependence on solar illumination of the ionosphere. When the effects of sunlight are eliminated, aurora is found to be more common during the summer. The occurrence of diffuse, as well as discrete aurora, is suppressed by solar illumination of the ionosphere. This dependence of diffuse auroral precipitation on ionospheric conditions is not predicted by theories that attribute diffuse aurora to equatorial pitch-angle diffusion of hot magnetospheric electrons.

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“…The basic characteristics of the satellite are described by Lundin et al [1994a]. In this study, we have primarily used density data measured by the cylindrical Langmuir probe of the F4 wave/plasma density instrument , together with data from the F3H ion instrument 2.…”

Section: Instrumentation and Datamentioning

confidence: 99%

Observations of mesoscale auroral plasma cavity crossings with the Freja satellite

Mäkelä¹,

Mälkki²,

Koskinen³

et al. 1998

J. Geophys. Res.

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Abstract. We have used data from the Freja satellite, with an apogee of 1700 km over the auroral oval, to make a statistical analysis of mesoscale auroral plasma density cavities. Such cavities are defined to be regions in the auroral zone with size scales between discrete arcs and inverted-V events in which the plasma density abruptly drops to less than 50% of the ambient plasma density. We present occurrence distributions by magnetic activity, local time, and magnetic latitude. It is found that cavity occurrence does not depend on magnetic activity. In contrast to earlier studies, we find cavities at all local times; however, a dawn-dusk asymmetry is found in the distribution. There is likewise a weak dawn-dusk asymmetry in the latitudinal distribution. Since our data cover a full year, seasonal dependence of cavity occurrence can also be investigated. We find a small seasonal trend, with cavities found more commonly during the dark season, but the trend is not quite statistically significant. We also study several plasma depletion processes that could be responsible for cavities at this altitude. The results suggest that more than one process is compatible with the distributions we find.

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The Freja Project

Cited by 45 publications

References 6 publications

Laboratory experiments on shear Alfvén waves and their relationship to space plasmas

Laboratory experiments on shear Alfvén waves and their relationship to space plasmas

The importance of solar illumination for discrete and diffuse aurora

Observations of mesoscale auroral plasma cavity crossings with the Freja satellite

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