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A MODEL FOR THE RADIAL VARIATION OF THE POWER SPECTRA OF THE IMF FLUCTUATIONS

TU CHUAN-YI (Department of Geophysics, Pelting University)  
A model for the radial variation of the power spectrum of the IMP fluctuations is presented in this paper. The basic idea is that the fluctuations in the frequency range round 10-4Hz propagating from the sun to the earth's orbit are nearly as predicted by the WKB Alfvén waves model, but a small part of energy cascades into the frequency range above 10-3 Hz, in which the fluctuations are controlled by the cascading process-Based on this idea, a power spectrum equation of the IMP fluctuations including a cascading term is presented and numerical solutions of the spectrum equation are given. The solutions show that the slope of the spectrum in the frequency range higher than 10-2 Hz nearly remains -1.6 while the slope of the spectrum in the low frequency range around 10-3 Hz increases from 0.3 AU to 1 AU. The average spectrum density over the frequency range 2.8×10-4Hz- 2.5×10-3 Hz varies with distance as r-3.5 while that over 1.0 × 10-2 Hz-8.3×10-2 Hz as r-4.1 in the space 0.3 AU to 1 AU. All of the properties calculated are consistent with the radial evolution of the power spectrum of IMP fluctuations first observed by Helios 1 and Helios 2 (Bavassano, 1982). The numerical solution shows that the energy flux of the fluctuations near the sun is of the order of 104 erg cm-2s-1, that is, the same as the wave energy flux some solar wind theories seem to require.
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