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Electron density power spectrum in the local interstellar mediumInterstellar scintillation (ISS), fluctuations in the amplitude and phase of radio waves caused by scattering in the interstellar medium, is important as a diagnostic of interstellar plasma turbulence. ISS is also of interest because it is noise for other radio astronomical observations. The unifying concern is the power spectrum of the interstellar electron density. Here we use ISS observations through the nearby (less than or approximately =1 kpc) (ISM) to estimate the spectrum. From measurements of angular broadening of pulsars and extragalactic sources, decorrelation bandwidth of pulsars, refractive steering of features in pulsar dynamic spectra, dispersion measured fluctuations of pulsars, and refractive scintillation index measurements, we construct a composite structure function that is approximately power law over 2 x 10(exp 6) m less than scale less than 10(exp 13) m. The data are consistent with the structure function having a logarithmic slope versus baseline less than 2; thus there is a meaningful connection between scales in the radiowave fluctuation field and the scales in the electron density field causing the scattering. The data give an upper limit to the inner scale, l(sub o) less than or approximately 10(exp 8) m and are consistent with much smaller values. We construct a composite electron density spectrum that is approximately power law over at least the approximately = 5 decade wavenumber range 10(exp -13)/m less than wavenumber less than 10(exp -8)/m and that may extend to higher wavenumbers. The average spectral index of electron density over this wavenumber range is approximately = 3.7, very close to the value expected for a Kolmogorov process. The outer scale size, L(sub o), must be greater than or approximately = 10(exp 13) m (determined from dispersion measure fluctuations). When the ISS data are combined with measurements of differential Faraday rotation angle, and gradients in the average electron density, constraints can be put on the spectrum at much smaller wave numbers. The composite spectrum is consistent with a Kolmogorov-like power law over a huge range (10 or more decades) of spatial wavenumber with an infrared outer scale L(sub o) greater than or approximately 10(exp 18)m. This power-law subrange-expressed as ratio of outer to inner scales-is comparable to or larger than that of other naturally occurring turbulent fluids, such as the oceans or the solar wind. We outline some of the theories for generating and maintaining such a spectrum over this huge wavenumber range.
Document ID
19950053584
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Armstrong, J. W.
(NASA Jet Propulsion Lab. Pasadena, CA, United States)
Rickett, B. J.
(Univ. of San Diego, La Jolla, CA United States)
Spangler, S. R.
(Univ. of Iowa, Iowa City, IA United States)
Date Acquired
August 16, 2013
Publication Date
October 4, 1995
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 443
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A85183
Funding Number(s)
CONTRACT_GRANT: NAGW-1594
CONTRACT_GRANT: NSF AST-89-16805
CONTRACT_GRANT: NSF ATM-92-16821
Distribution Limits
Public
Copyright
Other

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