Physics – Geophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh53a1297s&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH53A-1297
Physics
Geophysics
[2134] Interplanetary Physics / Interplanetary Magnetic Fields, [2149] Interplanetary Physics / Mhd Waves And Turbulence, [4490] Nonlinear Geophysics / Turbulence
Scientific paper
We examine the convergence of third-order structure function expressions derived to measure the rate of turbulent energy cascade within the solar wind using Advanced Composition Explorer observations from 1 AU over the years 1998 through 2007. We find that a minimum of a year of data is normally required to get good convergence and statistically significant results. We then apply these findings to ten years of observations spanning both solar minimum and solar maximum conditions. We compare the computed energy cascade rates with previously determined rates of proton heating at 1 AU as determined from the radial gradient of the proton temperature to be proportional to the product of wind speed and proton temperature. We find good agreement with a moderate excess of energy within the cascade that is consistent with previous estimates for thermal electron heating in the solar wind. In keeping with earlier analyses of the dissipation spectrum, we postulate that electron heating by the turbulent cascade is less than and at most equal to the rate of proton heating. We extend the analysis to study high cross-helicity states. In these cases we find a significant back transfer of energy within the inertial range that moves energy from small to large scales. This back transfer is primarily operating on what the second-order structure functions show to be the energetically dominant, outward-propagating modes causing a reinforcement of the observed cross helicity of this component. We further identify isolated regions of low shear such as high-speed winds far from interaction or expansion regions as the most common location of high cross-helicity states. In the process we search for evidence of changing spectral forms for the measured power spectra that would be consistent with recent theories of "unbalanced" turbulence and find questionable evidence that requires additional consideration.
Forman Miriam A.
MacBride Benjamin T.
Smith Walter C.
Stawarz Joshua E.
Tessein J.
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