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| Titel |
Spectral characteristics of high latitude raw 40 MHz cosmic noise signals |
| VerfasserIn |
C. M. Hall |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2198-5634
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics Discussions ; 2, no. 4 ; Nr. 2, no. 4 (2015-07-07), S.969-987 |
| Datensatznummer |
250115179
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| Publikation (Nr.) |
 copernicus.org/npgd-2-969-2015.pdf |
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| Zusammenfassung |
| Cosmic noise at 40 MHz is measured at Ny-Ålesund
(79° N, 12° E) using a relative ionospheric opacity
meter ("riometer"). A riometer is normally used to determine the
degree to which cosmic noise is absorbed by the intervening
ionosphere, giving an indication of ionization of the atmosphere at
altitudes lower than generally monitored by other instruments. The
usual course is to determine a "quiet-day" variation, this
representing the galactic noise signal itself in the absence of
absorption; the current signal is then subtracted from this to arrive
at absorption expressed in dB. By a variety of means and assumptions,
it is thereafter possible to estimate electron density profiles in the
very lowest reaches of the ionosphere. Here however, the entire
signal, i.e. including the cosmic noise itself will be examined and
spectral characteristics identified. It will be seen that distinct
spectral subranges are evident which can, in turn be identified with
non-Gaussian processes characterized by generalized Hurst exponents,
α. Considering all periods greater than 1 h, α ≈ 1.24 – an indication
of fractional Brownian motion, whereas for periods greater than 1 day α ≈ 0.9 – approximately pink
noise and just in the domain of fractional Gaussian noise. The results
are compared with other physical processes suggesting that
absorption of cosmic noise is characterized by a generalized
Hurst exponent ≈ 1.24 and thus non-persistent fractional
Brownian motion, whereas generation of cosmic noise is
characterized by a generalized Hurst exponent ≈ 1. |
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