On the role of auroral electric fields in the formation of low altitude sporadic-E and sudden sodium layers

Kirkwood, S.; Zahn, U. von

doi:10.1016/0021-9169(91)90034-5

Cited by 86 publications

(71 citation statements)

References 40 publications

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“…The fast changes in sporadic layer heights and densities give reason to assume the presence of strong electric fields shifting and collecting the ions from a bigger atmospheric volume (see e.g. Kirkwood and von Zahn (1991) of about 25 cm −3 below 95 km and 40 cm −3 above 95 km.…”

Section: Observations Of Neutral and Ionized Sporadic Metal Layers: Fmentioning

confidence: 99%

“…review by Clemesha (1995)). Nevertheless, there is a general consensus on the importance of the combination of wind shears and Lorentz forces as triggers for the formation of sporadic ion layers (Chimonas and Axford, 1968;Kirkwood and von Zahn, 1991;Höffner and von Zahn, 1994). Lacking quantitative information on the ambient winds and electric fields in our experiments, we have little to add to the discussion of the latter scenario.…”

Section: Interpretation Of Variations and Implications For The Formatmentioning

confidence: 99%

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Sporadic Ca and Ca<sup>+</sup> layers at mid-latitudes: Simultaneous observations and implications for their formation

et al. 2001

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Abstract. We report on the observations of 188 sporadic layers of either Ca atoms and/or Ca ions that we have observed during 112 nights of lidar soundings of Ca, and 58 nights of Ca + soundings, at Kühlungsborn, Germany (54 • N, 12 • E). The Ca + soundings have been performed simultaneously and in a common volume with the Ca soundings by two separate lidars. Correlations between sporadic neutral and ionized metal layers are demonstrated through four case studies. A systematic study of the variations of occurrence of sporadic Ca and Ca + layers reveals that neutral and ionized Ca layers are not as closely correlated as expected earlier: (a) The altitude distribution shows the simultaneous occurrence of both sporadic Ca and Ca + layers to be most likely only in the narrow altitude range between 90 and 95 km. Above that region, in the lower thermosphere, the sporadic ion layers are much more frequent than atom layers. Below 90 km only very few sporadic layers have been observed; (b) The seasonal variation of sporadic Ca layers exhibits a minimum of occurrence in summer, while sporadic Ca + layers do not show a significant seasonal variation (only the dense Ca + layers appear to have a maximum in summer). At midlatitudes sporadic Ca layers are more frequent than sporadic layers of other atmospheric metals like Na or K. For the explanation of our observations new formation mechanisms are discussed.

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Section: Observations Of Neutral and Ionized Sporadic Metal Layers: Fmentioning

confidence: 99%

Section: Interpretation Of Variations and Implications For The Formatmentioning

confidence: 99%

Sporadic Ca and Ca<sup>+</sup> layers at mid-latitudes: Simultaneous observations and implications for their formation

et al. 2001

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“…1), in particular below 110 km altitude. Kirkwood and von Zahn (1991) studied the role of auroral electric fields in simulations and comparisons with EISCAT observations and found that metallic sporadic layers can be formed between 90 and 105 km when the electric field is westward or southward to southeastward. Electric field effects can be much stronger; for example E/B ∼ (5 mV m −1 /0.05 mT) ∼ 100 m s −1 , while disturbed conditions can have horizontal fields of 40 mV m −1 or more.…”

Section: Sporadic E Layersmentioning

confidence: 99%

“…Kirkwood and von Zahn (1991) argued that in the electric field action that carries positive ions downward, negative dust particles would be carried upward. However, in our case, wind shear convergence maintaining the positive ion layer would result in divergence for negative ions.…”

Section: Electron Biteoutsmentioning

confidence: 99%

“…Mathews (1987) discusses the importance of neutral dust at the "dumping" region for sporadic E around 90 km and estimates the electron attachment rate to neutral dust particles. Beatty et al (1989) and Kirkwood and von Zahn (1991) pointed out the interaction between dust layers, sporadic E, and neutral metal layers, and that the presence of a charged dust layer would reduce the electric conductivity parallel to the magnetic field and result in charge separation and polarization electric fields. Plane et al (2014) find that, above the atomic oxygen ledge (typically 88-90 km), negatively charged dust particles of radii < 1 nm (and which contain silicon) are abundant and predominant over negative molecular ions.…”

Section: Electron Biteoutsmentioning

confidence: 99%

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Observation of electron biteout regions below sporadic E layers at polar latitudes

2015

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Abstract. The descent of a narrow sporadic E layer near 95 km altitude over Poker Flat Research Range in Alaska was observed with electron probes on two consecutive sounding rockets and with incoherent scatter radar during a 2 h period near magnetic midnight. A series of four trimethyl aluminum chemical releases demonstrated that the Es layer remained just slightly above the zonal wind node, which was slowly descending due to propagating long-period gravity waves. The location of the layer is consistent with the equilibrium position due to combined action of the wind shear and electric fields. Although the horizontal electric field could not be measured directly, we estimate that it was ∼ 2 mV m −1 southward, consistent with modeling the vertical ion drift, and compatible with extremely quiet conditions. Both electron probes observed deep biteout regions just below the Es enhancements, which also descended with the sporadic layers. We discuss several possibilities for the cause of these depletions; one possibility is the presence of negatively charged, nanometer-sized mesospheric smoke particles. Such particles have recently been detected in the upper mesosphere, but not yet in immediate connection with sporadic E. Our observations of electron depletions suggest a new process associated with sporadic E.

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Sporadic E ionization layers observed with radar imaging and ionospheric modification

Hysell

Munk

McCarrick

2014

Geophysical Research Letters

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Sporadic E ionization layers have been observed in the daytime subauroral ionospheric E layer by a 30 MHz radar in Alaska. The radar detects coherent backscatter from meter-scale field-aligned plasma density irregularities. The irregularities were generated by ionospheric modification-by the emission of strong HF electromagnetic waves directly beneath the layers-making the layers visible to the radar. Aperture-synthesis methods are used to generate imagery of the layers from the radar data. The layers are patchy, with patches organized along fronts spaced by tens of kilometers and propagating slowly toward the southwest. Similar, naturally occurring layers are commonly observed at middle latitudes at night in the absence of ionospheric modification. That the patchy layers can be found at high magnetic latitudes during the day argues that they are most likely produced through the interaction of the ionospheric layer with neutral atmospheric waves and instabilities. Attenuation of the radar echoes when the HF emission frequency exceeded the third harmonic of the electron gyrofrequency was observed and is discussed.

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On the role of auroral electric fields in the formation of low altitude sporadic-E and sudden sodium layers

Cited by 86 publications

References 40 publications

Sporadic Ca and Ca<sup>+</sup> layers at mid-latitudes: Simultaneous observations and implications for their formation

Sporadic Ca and Ca<sup>+</sup> layers at mid-latitudes: Simultaneous observations and implications for their formation

Observation of electron biteout regions below sporadic E layers at polar latitudes

Sporadic E ionization layers observed with radar imaging and ionospheric modification

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On the role of auroral electric fields in the formation of low altitude sporadic-E and sudden sodium layers

Cited by 86 publications

References 40 publications

Sporadic Ca and Ca&lt;sup&gt;+&lt;/sup&gt; layers at mid-latitudes: Simultaneous observations and implications for their formation

Sporadic Ca and Ca&lt;sup&gt;+&lt;/sup&gt; layers at mid-latitudes: Simultaneous observations and implications for their formation

Observation of electron biteout regions below sporadic E layers at polar latitudes

Sporadic E ionization layers observed with radar imaging and ionospheric modification

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Resources

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Sporadic Ca and Ca<sup>+</sup> layers at mid-latitudes: Simultaneous observations and implications for their formation

Sporadic Ca and Ca<sup>+</sup> layers at mid-latitudes: Simultaneous observations and implications for their formation