Spectral characteristics of high latitude raw 40MHz cosmic noise signals
Permanent lenke
https://hdl.handle.net/10037/7973DOI
doi:10.5194/npgd-2-969-2015Dato
2015-07-07Type
Journal articleTidsskriftartikkel
Peer reviewed
Forfatter
Hall, ChrisSammendrag
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.
Forlag
Copernicus PublicationsSitering
Nonlinear Processes in Geophysics Discussions 2(2015) s. 969-987Metadata
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