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| Titel |
Electric field measurements of DC and long wavelength structures associated with sporadic-E layers and QP radar echoes |
| VerfasserIn |
R. Pfaff, H. Freudenreich, T. Yokoyama, M. Yamamoto, S. Fukao, H. Mori, S. Ohtsuki, N. Iwagami |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 23, no. 7 ; Nr. 23, no. 7 (2005-10-13), S.2319-2334 |
| Datensatznummer |
250015307
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| Publikation (Nr.) |
 copernicus.org/angeo-23-2319-2005.pdf |
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| Zusammenfassung |
| Electric field and plasma density data gathered on a sounding rocket
launched from Uchinoura Space Center, Japan, reveal a complex
electrodynamics associated with sporadic-E layers and simultaneous
observations of quasi-periodic radar echoes. The electrodynamics are
characterized by spatial and temporal variations that differed considerably
between the rocket's upleg and downleg traversals of the lower ionosphere.
Within the main sporadic-E layer (95–110 km) on the upleg, the electric
fields were variable, with amplitudes of 2–4 mV/m that changed considerably
within altitude intervals of 1–3 km. The identification of polarization
electric fields coinciding with plasma density enhancements and/or
depletions is not readily apparent. Within this region on the downleg,
however, the direction of the electric field revealed a marked change that
coincided precisely with the peak of a single, narrow sporadic-E plasma
density layer near 102.5 km. This shear was presumably associated with the
neutral wind shear responsible for the layer formation. The electric field
data above the sporadic-E layer on the upleg, from 110 km to the rocket
apogee of 152 km, revealed a continuous train of distinct, large scale,
quasi-periodic structures with wavelengths of 10–15 km and wavevectors
oriented between the NE-SW quadrants. The electric field structures had
typical amplitudes of 3–5 mV/m with one excursion to 9 mV/m, and in a very
general sense, were associated with perturbations in the plasma density. The
electric field waveforms showed evidence for steepening and/or convergence
effects and presumably had mapped upwards along the magnetic field from the
sporadic-E region below. Candidate mechanisms to explain the origin of these
structures include the Kelvin-Helmholtz instability and the Es-layer
instability. In both cases, the same shear that formed the sporadic-E layer
would provide the energy to generate the km-scale structures. Other
possibilities include gravity waves or a combination of these processes.
The data suggest that these structures were associated with the lower
altitude density striations that were the seat of the QP radar echoes
observed simultaneously. They also appear to have been associated with the
mechanism responsible for a well-defined pattern of "whorls" in the
neutral wind data that were revealed in a chemical trail released by a
second sounding rocket launched 15min later. Short scale (<100 m)
electric field irregularities were also observed and were strongest in the
sporadic-E region below 110km. The irregularities were organized into 2–3
layers on the upleg, where the plasma density also displayed multiple
layers, yet were confined to a single layer on the downleg where the plasma
density showed a single, well-defined sporadic-E peak. The linear gradient
drift instability involving the DC electric field and the vertical plasma
gradient is shown to be incapable of driving the observed waves on the
upleg, but may have contributed to the growth of short scale waves on the
topside of the narrow unstable density gradient observed on the downleg. The
data suggest that other sources of free energy may have been important
factors for the growth of the short scale irregularities.
Keywords. Ionosphere (Mid-latitude ionosphere; Electric
fields and currents; Ionospheric irregularities) |
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