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2019-04-19 Abstract

Title: In situ observations of interstellar electron turbulence spectrum by Voyager 1
Speaker:  Dr. Kun-Han Lee  (Institute of Earth Sciences, Academia Sinica)
Date: April 19 at 15:30
Location: R521, General building II
In 1976, Lee and Jokipii first suggested that the interstellar turbulence at the length scale λ of 108m to 1018m (100 light-years) has a Kolmogorov-like spectrum based on observations of radio wave scintillations and interstellar clouds. The scintillations of pulsar radio wave by interstellar turbulent electrons provide the turbulence power at the scale λ=108m, and the observations of interstellar clouds provide the turbulence power at λ=1018m. The slope of the line connecting the powers in logarithmic scale at λ=108m and at λ=1018m is about -11/3. Many later ground observations confirmed this speculation. Armstrong et al. (1995) constructed the composite spectrum extending from 106.4m to 1018m, a.k.a. the Big Power Law in the sky, based on several observational results. In the present study, the interstellar turbulence spectrum of electron density is obtained for the first time from in situ observations of Voyager 1. The observed spectrum extends from λ=q-1=15AU≈2.25×1012m (q=4.4×10-13m-1) to λ=50m (q=2×10-2m-1), close to the Debye length. The measured spectrum covers part (q=4.4×10-13m-1 - 1×10-6m-1) of the Kolmogorov inertial range as well as ion and electron kinetic scales (q=1×10-6m-1 - 2×10-2m-1). The observed Kolmogorov inertial range shows a good agreement with earlier studies. Around the kinetic scales, a bulge of spectral intensity higher than the Kolmogorov spectrum is found.


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