Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh44a..05s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #SH44A-05
Other
7863 Turbulence, 7867 Wave/Particle Interactions, 2149 Mhd Waves And Turbulence, 2159 Plasma Waves And Turbulence, 2164 Solar Wind Plasma
Scientific paper
The solar wind is a collisionless, strongly turbulent plasma in a supersonic and super-Alfvénic spherical expansion. One of its most striking features is the very large number of degrees of freedom that are excited: the electromagnetic fields and plasma properties of the solar wind show fluctuations over a very wide range of time scales, ranging from the solar rotation period down to the local electron plasma period, i.e. for frequencies f from 10-6 Hz up to fpe ˜ 2ṡ 104 Hz. We present and discuss here a global spectrum (2 months average) of solar wind electromagnetic fluctuations over the above-mentioned frequency range, obtained using data from several instruments on the WIND spacecraft at 1 AU near L1. The observed power spectrum shows a power-law f-5/3 in the Alvénic frequency range, between 10-4 to 0.4 Hz, but it steepens to roughly f-3 up to the local electron cyclotron frequency ( fce ˜ 100 - 200 Hz). It is now widely recognized that the f-5/3 spectrum is the "inertial range" of MHD turbulence in the solar wind, resulting from a nonlinear energy cascade operating from the large "energy containing" scales to smaller scales where dissipation is presumed to act. The aim of this paper is to address both questions of turbulence and dissipation in the solar wind at 1 AU. For that, I will present new results of recent investigations using WIND data at 1 AU near L1, covering both the inertial and the f-3 ranges. In a first part, results on the scaling properties and intermittent character of solar wind fluctuations in the inertial range will be discussed. The spectral steepening around 0.4 Hz is commonly believed to be due to collisionless ion-cyclotron damping of Alfvénic-like fluctuations present in the inertial range. But, is damping really the dominant effect or is the f-3 power-law from 0.4 Hz to fce sustained by some other kinetic effects that would overcome damping, as pointed out by some recent theoretical interpretations? To address this question, in a second part, i will discuss the nature of the fluctuations in this range, their properties, their possible source(s) and their role in the control of the energy transport in the solar wind.
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