The power spectrum of interplanetary Alfvénic fluctuations: Derivation of the governing equation and its solution

摘要: A model is presented to explain the radial evolution of power spectra interplanetary Alfvenic fluctuations found by Bavassano et al. (1982a) based on magnetic field data Helios 1 and 2. It assumed in this that represent an asymmetric state MHD turbulence which most are wave mode propagating outward from sun, with a small part inward. There weak nonlinear interaction between two modes. also will not become dissociated sources create waves inward remain 0.3 AU AU. The results energy cascading process. Both effects process slow variation solar wind determine spectra. Starting magnetohydrodynamic equations deriving governing correlation moments, we finally get equation describes spectrum. We present analytic solution. given analytical solution, 0.29 0.87 AU, agreement observation 2 following aspects: (1) spectral slope increases (in absolute value) for frequency range lower than 2.5×10−3 Hz while remains almost unchanged higher 10−1.5 Hz. (2) gradient spectrum densities increasing frequency. dissipation length nearly f ≥ 10−2 (3) 〈b²〉 approximately r−3.56. (4) ratio 〈b²〉/Bo² constant.