Electric fields and conductivity in the nighttime E‐region: A new magnetosphere‐ionosphere‐atmosphere coupling effect

Banks, Peter M.; Yasuhara, F.

doi:10.1029/gl005i012p01047

Cited by 59 publications

(54 citation statements)

References 4 publications

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“…The cause and effect may be the opposite, as discussed above, with downward current systems associated with magnetospheric processes causing low density and thus low conductance regions in the ionosphere. This phenomenon, "E-region cavity formation", has been modeled by Banks and Yasuhara (1978); Doe et al (1995); Karlsson and Marklund (1998), and cavity formation against a solar EUV produced E-region background in the dayside cusp region was observed by Nilsson et al (1998). Such cavity formation may in turn contribute to further ionospheric feedback, as modeled by Streltsov and Lotko (2002).…”

Section: Introductionmentioning

confidence: 99%

Radar observations in the vicinity of pre-noon auroral arcs

et al. 2005

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Abstract.A combination of EISCAT incoherent scatter radar measurements, optical and magnetometer data is used to study the plasma in and around pre-noon structured precipitation and auroral arcs. Particular attention is paid to regions of comparatively low E-region density observed adjacent to arcs or structured precipitation in the EISCAT Svalbard radar field-aligned measurements. Comparison between luminosity and incoherent scatter electron density measurements shows that the low-density regions occur primarily due to the absence of diffuse precipitation rather than to a cavity formation process. Two cases of arcs and low density/luminosity regions are identified. The first is related to a strong Pc5 pulsation event, and the absence of diffuse precipitation is due to a large-scale modulation of the diffuse precipitation. In the second case the equatormost arc is on a shielding boundary and the low-density region coincides with a strong flow region just poleward of this arc. Regions of high electric field and low luminosity and conductance are observed prior to intensification of the structured precipitation in both cases. The ionospheric current is enhanced in the low conductance region, indicating that the strong electric fields do not result solely from ionospheric polarization electric fields, and thus are mainly driven by magnetospheric processes. The average energy of the precipitating electrons in the arcs and structured precipitation is, according to EIS-CAT measurements, 500 eV and the energy spectra are similar for the pulsation and shielding cases. The average energy is thus significantly less than in the diffuse precipitation region which shows central CPS-like energy spectra. We suggest that the low ionospheric conductance of 0.7 S in the low density regions is favorable for the arc formation process. This is in quantitative agreement with recent simulations of the ionospheric feedback instability.

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Section: Introductionmentioning

confidence: 99%

Radar observations in the vicinity of pre-noon auroral arcs

et al. 2005

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“…The larger scale size is the ~4.5° latitudinal width of the SAPS structure and the smaller one is that of the plasma irregularity structures. The coincidental formation of plasma density troughs and SAPS structures was predicted based on theoretical considerations by Schunk et al [1976] and Banks and Yasuhara [1978]. They argued that intense electric fields in the subauroral ionosphere would lead to the formation of deep troughs through a combination of plasma outflow and enhanced recombination stemming from the charge exchange reaction O^ + N2 -> NO^ + N whose rate k^j^ increases in the convecting/ heated plasma.…”

Section: Source For Observed Plasma Irregularitiesmentioning

confidence: 99%

Electromagnetic Wave Structures Within Subauroral Polarization Streams

Mishin¹,

Burke²,

Huang³

et al. 2003

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“…Banks and Yasuhara (1978) reported that large poleward electric fields have the effect of substantially reducing the Pedersen and Hall conductivities on the equatorward side of this region. This effect, in turn, influences the spatial distribution of field-aligned currents (FAC), and reduces the magnitude of current needed to support the imposed electric field.…”

Section: Introductionmentioning

confidence: 99%

Investigation of subauroral ion drifts and related field-aligned currents and ionospheric Pedersen conductivity distribution

2004

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Abstract. Based on Astrid-2 satellite data, results are presented from a statistical study on subauroral ion drift (SAID) occurrence. SAID is a subauroral phenomenon characterized by a westward ionospheric ion drift with velocity greater than 1000 m/s, or equivalently, by a poleward-directed electric field with intensity greater than 30 mV/m. SAID events occur predominantly in the premidnight sector, with a maximum probability located within the 20:00 to 23:00 MLT sector, where the most rapid SAID events are also found. They are substorm related, and show first an increase in intensity and a decrease in latitudinal width during the expansion phase, followed by a weakening and widening of the SAID structures during the recovery phase. The potential drop across a SAID structure is seen to remain roughly constant during the recovery phase.The field-aligned current density and the height-integrated Pedersen conductivity distribution associated with the SAID events were calculated. The results reveal that the strongest SAID electric field peaks are associated with the lowest Pedersen conductivity minimum values. Clear modifications are seen in the ionospheric Pedersen conductivity distribution associated with the SAID structure as time evolves: the SAID peak is located on the poleward side of the corresponding region of reduced Pedersen conductivity; the shape of the regions of reduced conductivity is asymmetric, with a steeper poleward edge and a more rounded equatorward edge; the SAID structure becomes less intense and widens with evolution of the substorm recovery phase. From the analysis of the SAID occurrence relative to the mid-latitude trough position, SAID peaks are seen to occur relatively close to the corresponding mid-latitude trough minimum. Both these features show a similar response to magnetospheric disturbances, but on different time scales -with increasing magnetic activity, the SAID structure shows a faster movement towards lower latitudes than that of the mid-latitude trough.From the combined analysis of these results, we conclude that the SAID generation mechanism cannot be regarded ei- ther as a pure voltage generator or as a pure current generator, applied to the ionosphere. While the anti-correlation between the width and the peak intensity of the SAID structures with substorm evolution indicates a magnetospheric source acting as a constant voltage generator, the ionospheric modifications and, in particular the reduction in the conductivity for intense SAID structures, are indicative of a constant current system closing through the ionosphere. The ionospheric feedback mechanisms are seen to be of major importance for sustaining and regulating the SAID structures.

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Electric fields and conductivity in the nighttime E‐region: A new magnetosphere‐ionosphere‐atmosphere coupling effect

Cited by 59 publications

References 4 publications

Radar observations in the vicinity of pre-noon auroral arcs

Radar observations in the vicinity of pre-noon auroral arcs

Electromagnetic Wave Structures Within Subauroral Polarization Streams

Investigation of subauroral ion drifts and related field-aligned currents and ionospheric Pedersen conductivity distribution

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