On a threshold electric field associated with the 398-MHz diffuse radar aurora

Tsunoda, Roland T.; Presnell, R. I.

doi:10.1029/ja081i001p00088

Cited by 34 publications

(17 citation statements)

References 24 publications

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“…Strong experimental evidence for this relationship has been found recently by ECKLUND et al (1977) andCAHILL et al (1978). The only serious problem in observing auroral zone electric fields with this type of radar is that a threshold electric field apparently is needed to excite the plasma irregularities in the ionosphere (TSUNODA and PRESNELL, 1976;SIREN et al, 1977). CAHILL et al (1978) found threshold values of 15-20mVm-1 for the STARE radars.…”

Section: Instrumentationmentioning

confidence: 87%

Joint two-dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents. 2. Three-dimensional current flow in the morning sector during substorm recovery.

Baumjohann

Kamide

1981

J. geomagn. geoelec

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By using two-dimensional observations of ground magnetic perturbations with the Scandinavian Magnetometer Array and by incorporating some simultaneous electric field observations made by the STARE radars, an attempt is made to model the threedimensional current system in the late morning sector during a substorm recovery phase on February 16, 1977. During the recovery phase of substorm activity a localized region of net upward field-aligned current drifts to the east. This current is apparently carried by drift precipitation of energetic electrons which has been observed earlier by balloon and satellite spectrometers under the same geophysical conditions. The precipitating electrons responsible for the upward field-aligned current seem to shortcircuit the westward electrojet Hall current and cause its divergence up magnetic field lines. Equatorward of the auroral oval the precipitating electrons create a high-conducting channel where an eastward current is flowing. This current is probably a Cowling current and is decreasing in the eastward direction. While it remains open how this current is fed into the ionosphere, we content that the total eastward current is also diverging up magnetic field lines.

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Section: Instrumentationmentioning

confidence: 87%

Joint two-dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents. 2. Three-dimensional current flow in the morning sector during substorm recovery.

Baumjohann

Kamide

1981

J. geomagn. geoelec

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“…Eather [1967] pointed out that emission from the proton aurora rarely exceeds 200 R. For the ionization rate profiles presented by Eather [1970] only 104 el/cm 8. Tsunoda and Presnell [1976] showed that the diffuse auroral echoes can be observed with the 398-MHz Homer radar only when the electron density exceeds few parts times 104 el/cm 8. But on the other hand, the peak electron densities associated with the diffuse radar aurora are typically no more than a few parts times 105 el/cm 3 (R. T. Tsunoda, unpublished data, 1974).…”

Section: Discussionmentioning

confidence: 99%

“…In that event the DB was associated only with the steepest portion of the downward field-aligned current region, that nearest the poleward boundary. The absence of auroral echoes in the region of less intense DFAC can be accounted for if we assume that the ionospheric electric field strength in that region was below the threshold electric field value[Tsunoda and Presnell, 1976]. Therefore the results indicate that the DFAC is collocated with the DB and hence with the eastward electrojet.In the following, we present several of the more interesting examples showing the actual spatial comparison between the radar aurora and field-aligned currents.…”

mentioning

confidence: 90%

“…was very low in regions poleward of the DB that were not occupied by the visual arcs. Tsunodaand Presnell [1976] found that auroral echoes were not observed on the phased array radar when the electron density was below a few parts times 104 el/cm 8, even when the electric field strength was above the threshold level. Thedecrease in electron density poleward of the DB suggests a particle precipitation boundary [Romick et al, 1974; Tsunoda et al, 1974].…”

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confidence: 99%

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The spatial relationship between the evening radar aurora and field-aligned currents

Tsunoda¹,

Presnell²,

Potemra³

1976

J. Geophys. Res.

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In recent years the diffuse radar aurora has been shown to be closely associated with the auroral electrojets. Greenwald et al. (1973, 1975) showed that the range‐integrated amplitude of the diffuse radar aurora is linearly proportional to the horizontal component of the magnetic perturbations found beneath the echoing region. Tsunoda et al. (1974) showed that the evening diffuse radar aurora was characterized by a distinct poleward boundary that was usually aligned along a magnetic L shell. They hypothesized that such a boundary could be produced by a latitudinal gradient in either the ionospheric electric field or the conductivity. In either case, field‐aligned currents might be expected to flow in such a region. An initial study was therefore undertaken to examine the spatial relationship of the radar aurora to the field‐aligned currents observed by virtue of the transverse magnetic disturbances detected by the Triad satellite. By utilizing a 398‐MHz phased array radar located at Homer, Alaska, event‐by‐event comparisons were made between the evening radar aurora and the field‐aligned currents in the 1700–2100 MLT sector. The results of this study include the following findings: (1) the downward field‐aligned currents in the evening sector are closely associated with the eastward electrojet; (2) the upward field‐aligned currents in the same time sector are associated with the visual aurora; (3) there is a poleward‐directed electric field across the oppositely directed field‐aligned currents, implying at least partial closure through the ionosphere via a Pedersen current; and (4) the downward field‐aligned currents are associated with the diffuse particle precipitation responsible for the production of the diffuse radar aurora (and hence the eastward electrojet). However, the downward field‐aligned currents must be carried by precipitating protons and/or upward‐moving low‐energy electrons.

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“…Since these were polar cap measurements the ionosphere was well behaved and the possibility of great changes in the acoustic speed due to electron heating less likely. TSUNODA and PRESNELL (1976) have shown a 30mV/m threshold for backscatter at 398MHz by comparing their auroral zone diffuse echoes to simultaneous Chatanika E field measurements. Thus it seems that the Farley-Buneman two-stream instability is the primary mechanism at the high latitudes.…”

Section: Instabilities In the Lower Ionosphere Driven By Perpendiculamentioning

confidence: 99%

A review of electrostatic wave measurements on auroral magnetic field lines.

Kelley

1978

J. geomagn. geoelec

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This review emphasizes experimental evidence for electrostatic waves on auroral zone magnetic field lines. Data were obtained from radar, balloon, rocket, and satellite observations. The paper is organized around three topics: (1) the turbulent density and velocity fields of the magnetospheric flow, (2) instabilities associated with the convection electric field and its interactions with the neutral atmosphere, and (3) waves and discontinuities in the dynamic region at about one Earth radius above the auroral zone. Measurements of both the electric field and density fluctuation component of such waves will be included. Although this is not a theoretical study, an attempt is made to organize the measurements about the existing theoretical framework.

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On a threshold electric field associated with the 398-MHz diffuse radar aurora

Cited by 34 publications

References 24 publications

Joint two-dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents. 2. Three-dimensional current flow in the morning sector during substorm recovery.

Joint two-dimensional observations of ground magnetic and ionospheric electric fields associated with auroral zone currents. 2. Three-dimensional current flow in the morning sector during substorm recovery.

The spatial relationship between the evening radar aurora and field-aligned currents

A review of electrostatic wave measurements on auroral magnetic field lines.

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