Polar cap sporadic E
Backscatter probings (at 28 MHz) of the arctic ionosphere were made at Alert, Canada, for almost two years. A skewed distribution around the site was found with (a) maximum occurrences constrained to the northeast within ±30° of the great circle through Alert and the principal northern magnetic dip...
| Published in: | Canadian Journal of Physics |
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| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
1969
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/p69-116 http://www.nrcresearchpress.com/doi/pdf/10.1139/p69-116 |
| Summary: | Backscatter probings (at 28 MHz) of the arctic ionosphere were made at Alert, Canada, for almost two years. A skewed distribution around the site was found with (a) maximum occurrences constrained to the northeast within ±30° of the great circle through Alert and the principal northern magnetic dip pole, (b) a secondary maximum to the south, and (c) a marked dearth of observations as a tongue from the west (250°–280°) to about 800 km in the east. The annual pattern was almost identical with the summer and winter patterns. Equinoctial distributions were distinct. The maximum broadened to include the sector in the northeast within the great circles passing through Alert and the dip pole, and Alert and the geomagnetic pole. The secondary maximum and the tongue from the west of very low occurrences vanished.Seasonally, a pronounced maximum was found in the period June–August, and a weak secondary maximum during the equinoctial months. Diurnally, activity was present from 0700–1900 LST with a single peak near 1300 LST. Slight deviations from this pattern were noted in winter and summer. In the equinoxes, a plateau or double peak seemed present in the afternoon.Returns from the azimuth of Thule correlated with vertical-incidence sporadic E frequencies from Thule multiplied by the secant factor. No correlation with similar data from Resolute Bay was present. Indications of direct backscatter from field-aligned irregularities were found despite the large angles off perpendicularity. Es occurrences, after a lag of 1–2 days, seemed to be associated with appreciable increases in the daily value of a p . None of the results were predicted by standard maximum usable frequency prediction procedures.Two mechanisms seem possible for clarifying the results: (a) for the summer maximum, the Es layer tilted upwards to the principal northern dip pole; and (b) for the secondary equinoctial maximum, the daily swing of the auroral oval through the antenna beamwidth. |
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