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Temporal properties of magnetospheric line radiation

Rodger, Craig J.; Clilverd, Mark A.; Yearby, Keith H.; Smith, Andy J.. 2000 Temporal properties of magnetospheric line radiation. Journal of Geophysical Research, 105 (A1). 329-336. 10.1029/1999JA900420

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Abstract/Summary

Magnetospheric line radiation (MLR) events are relatively narrowband VLF signals that sometimes drift in frequency and have been observed in both ground-based and satellite data sets. We present the results of a survey undertaken on the basis of measurements made of MLR events observed at Halley, Antarctica (75°30′S, 26°54′W, L ≈ 4.3), in June, July, September, and December 1995, specifically looking at the temporal properties of Halley MLR events. We find that (1) single MLR lines described in previous papers tend to be comprised of up to 3 lines with widths of 5–10 Hz. (2) The multiple lines show highly variable spacings (e.g., < 10 to ∼100 Hz). (3) The rate at which MLR lines appears from the noise is ∼0.1 to 0.2 dB s−1, considerably smaller than previously reported for other VLF emissions. MLR exhibits slow growth, relative frequency stability, and long lifetimes in comparison with other coherent whistler mode emissions and thus may be generated by a separate mechanism. (4) The diurnal occurrence of MLR observed at Halley is twin-peaked, indicating an association with a combination of chorus and midlatitude hiss. (5) MLR occurrence rates can vary greatly within a given month, but the proportion of MLR present as part of the overall Halley wave activity is roughly constant (10–13%) throughout the year. (6) The occurrence of MLR activity at Halley is weakly linked to geomagnetic activity but only 24–48 hours after very large storms (Kp > 6), which affects only 8% of the total MLR events in this study. For smaller storms, there is little effect, although MLR events tend not to occur when the geomagnetic activity has been quiet in the previous 48 hours. (7) There is no dependence of MLR occurrence rates upon the instantaneous levels of geomagnetic activity. (8) The average duration of a typical MLR event at Halley is ∼ 30 min, quite similar to previous reports.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1029/1999JA900420
Programmes: BAS Programmes > Pre 2000 programme
ISSN: 0148-0227
Additional Keywords: magnetospheric line radiation, MLR, geomagnetic activity, power line harmonic radiation, PHLR
Date made live: 03 Jul 2013 12:40 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/502371

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