Statistics of the lower hybrid wave cavities detected by the FREJA satellite

Kjus, Solveig Helene Høymork; Pécseli, H. L.; Lybekk, B.; Holtet, J. A.; Trulsen, J.; Lühr, H.; Eriksson, Anders

doi:10.1029/98ja02245

Cited by 36 publications

(41 citation statements)

References 18 publications

(8 reference statements)

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“…A recent analysis of Freja data [Kjus et al, 1998] discusses the basic statistical characteristics of lower hybrid waves and associated density depletions. In the observational part of their paper, Kjus In conclusion, we have shown that when lower hybrid wave radiation impinges on a density striation in a controlled experiment, the interaction produces large field amplitudes in the gradient regions.…”

Section: Summary Of Results and Conclusionmentioning

confidence: 99%

A three‐dimensional experimental study of lower hybrid wave interactions with field‐aligned density depletions

Rosenberg¹,

Gekelman²

2001

J. Geophys. Res.

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Abstract. Rocket observations of spatially localized bursts of intense lower hybrid wave radiation have been made for decades. As the ability of rocket observations to measure small-scale structure increases, scientists are better able to understand the physics responsible for the observations. However, rocket measurements are limited in their ability to fully diagnose the phenomenon they seek to measure. Therefore a laboratory experiment was undertaken at the Large Plasma Device (LAPD) at the University of California at Los Angeles to study the interaction of lower hybrid waves with a fieldaligned density depletion. The laboratory parameters were chosen to mimic the physics in the ionosphere. Laboratory experiments allow one not only to study the effect of different interaction parameters, like wave frequency or striation size, but also to fully diagnose the wave fields in three spatial dimensions and time. These experiments have shown that large-amplitude wave fields are localized to the areas of largest density gradient. The field pattern is independent of striation size and shape. The experimental results relate strongly to space-based observations. The laboratory results, therefore, can act as a guidepost to assist the understanding of the more complex and difficult-to-understand plasmas encountered in the ionosphere. IntroductionThe topic of wave interactions with plasma nonuniformities is a rich field which is now under investigation in the laboratory. The natural evolution of laboratory experiments to study these interactions should hold interest for those in the space physics community. Space, ionospheric, and magnetospheric plasmas are nonuniform in some way. A well-designed laboratory experiment has the potential to provide measurements in detail far greater than can currently be obtained by in situ measurements. Such detail can provide new insight into the physical mechanisms involved and can help direct the development of theories to explain the space-based observations. The observation of lower hybrid wave interactions with a field-aligned density depletion by sounding rockets in the ionosphere provided the inspiration for a series of laboratory experiments at the Large Plasma Device (LAPD) at the University of California at Los Angeles (UCLA). These experiments were designed so that their results would not only provide information about the wave/plasma nonuniformity interaction in general but also provide information about the ionospheric observations. Lower hybrid wave radiation has been observed in the ionosphere for decades [e. were not able to make any statement about the relationship of these bursts, which they called "spikelets," to changes in the plasma density. In fact, while they believed that these spikelets could be stationary structures, they could not discount the possibility that the structures moved at the ion drift velocity. They were, however, able to demonstrate a correlation between the spikelets and transverse ion acceleration. Ions accelerated at the rocket altitudes (450-650 ...

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Section: Summary Of Results and Conclusionmentioning

confidence: 99%

A three‐dimensional experimental study of lower hybrid wave interactions with field‐aligned density depletions

Rosenberg¹,

Gekelman²

2001

J. Geophys. Res.

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“…These are values in an inertial frame of reference. On Cluster, the plasma drift speed generally dominates over the spacecraft speed in this frame, so that the number of LHCs encountered in the plasma reference frame The occurrence frequency for some of the Freja orbits has been determined by Kjus et al (1998) to be about 2 per kilometer perpendicular to the magnetic field. The LHCs thus were a factor 2000 more common per kilometer in the Freja data compared to Cluster.…”

Section: Discussion Of Occurrence Statisticsmentioning

confidence: 99%

“…It is of interest to see where the LHCs are found in the Viking and Cluster data, so that we can compare with occurrence investigations from the Freja satellite Kjus et al, 1998). We also compare how common the LHCs are in the inner magnetosphere with those observations from the upper ionosphere.…”

Section: Location Of the Lhcsmentioning

confidence: 99%

Observations of lower hybrid cavities in the inner magnetosphere by the Cluster and Viking satellites

et al. 2004

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Abstract.Observations by the Viking and Cluster satellites at altitudes up to 35 000 km show that Lower Hybrid Cavities (LHCs) are common in the inner magnetosphere. LHCs are density depletions filled with waves in the lower hybrid frequency range. The LHCs have, until recently, only been found at altitudes up to 2000 km. Statistics of the locations and general shape of the LHCs is performed to obtain an overview of some of their properties. In total, we have observed 166 LHCs on Viking during 27 h of data, and 535 LHCs on Cluster during 87 h of data. These LHCs are found at invariant latitudes from the auroral region to the plasmapause. A comparison with lower altitude observations shows that the LHC occurrence frequency does not scale with the flux tube radius, so that the LHCs are moderately rarer at high altitudes. This indicates that the individual LHCs do not reach from the ionosphere to 35 000 km altitude, which gives an upper bound for their length. The width of the LHCs perpendicular to the geomagnetic field at high altitudes is a few times the ion gyroradius, consistent with observations at low altitudes. The estimated depth of the density depletions vary with altitude, being larger at altitudes of 20 000-35 000 km (Cluster, 10-20%), smaller around 1500-13 000 km (Viking and previous Freja results, a few percent) and again larger around 1000 km (previous sounding rocket observations, 10-20%). The LHCs in the inner magnetosphere are situated in regions with background electrostatic hiss in the lower hybrid frequency range, consistent with investigations at low altitudes. Individual LHCs observed at high altitudes are stable at least on time scales of 0.2 s (about the ion gyro period), which is consistent with previous results at lower altitudes, and observations by the four Cluster satellites show that the occurrence of LHCs in a region in space is a stable phenomenon, at least on time scales of an hour.

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“…The sounding rockets, which move slowly and have high telemetry bandwidth, have provided great detail for just a few events (e.g. Pinçon et al, 1997), while Freja, in its nearly three years of operation, yielded a wealth of observations providing occurrence statistics Kjus et al, 1998). It is of great interest to supplement the Freja results from 1500-1750 km altitudes with statistics from the Astrid-2 altitude of 1000 km.…”

Section: Scientific Objectivesmentioning

confidence: 99%

LINDA – the Astrid-2 Langmuir probe instrument

Holback

Jacksén²,

Åhlén

et al. 2001

Ann. Geophys.

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Abstract. The Swedish micro-satellite Astrid-2, designed for studies in magnetosperic physics, was launched into orbit on 10 December 1998 from the Russian cosmodrome Plesetsk. It was injected into a circular orbit at 1000 km and at 83 degrees inclination. The satellite carried, among other instruments, a double Langmuir Probe instrument called LINDA (Langmuir INterferometer and Density instrument for Astrid-2). The scientific goals of this instrument, as well as the technical design and possible modes of operation, are described. LINDA consists of two lightweight deployable boom systems, each carrying a small spherical probe. With these probes, separated by 2.9 meters, and in combination with a high sampling rate, it was possible to discriminate temporal structures (waves) from spatial structures. An onboard memory made it possible to collect data also at times when there was no ground contact. Plasma density and electron temperature data from all magnetic latitudes and for all seasons have been collected.

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Statistics of the lower hybrid wave cavities detected by the FREJA satellite

Cited by 36 publications

References 18 publications

A three‐dimensional experimental study of lower hybrid wave interactions with field‐aligned density depletions

A three‐dimensional experimental study of lower hybrid wave interactions with field‐aligned density depletions

Observations of lower hybrid cavities in the inner magnetosphere by the Cluster and Viking satellites

LINDA – the Astrid-2 Langmuir probe instrument

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