On the energy cascade rate of solar wind turbulence in high cross helicity flows

Details On the energy cascade rate of solar wind turbulence in high cross helicity flows On the energy cascade rate of solar wind turbulence in high cross helicity flows

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11605101p&link_type=abstract

Journal of Geophysical Research, Volume 116, Issue A5, CiteID A05101

Physics

Geophysics

1

Interplanetary Physics: Mhd Waves And Turbulence (2752, 6050, 7836), Interplanetary Physics: Plasma Waves And Turbulence, Interplanetary Physics: Solar Wind Plasma, Nonlinear Geophysics: Turbulence (3379, 4568, 7863), Nonlinear Geophysics: Cascades

Scientific paper

Improved observations and analysis of solar wind fluctuations at 1 AU show that the total energy spectrum, kinetic plus magnetic, is in better agreement with the Kraichnan 3/2 scaling than with the Kolmogorov 5/3 scaling, consistent with simulations of incompressible MHD turbulence with a strong ambient magnetic field which exhibit a perpendicular energy spectrum proportional to k$\perp$-3/2. The Kraichnan scaling is especially clear in solar wind flows having large values of the normalized cross helicity σc. In this study, a generalization of Boldyrev's theory that applies to turbulence with nonvanishing cross helicity is used to estimate the energy cascade rate for high cross helicity flows in the solar wind at 1 AU. The analysis of 85 intervals of solar wind data from the Wind spacecraft characterized by normalized cross helicities in the range ∣σc∣ > 0.88 yields typical values of the energy dissipation rate $\varepsilon$ ranging from 100 to 2400 J/kg/s. This is roughly a factor of 4 or 5 smaller than estimates of the proton heating rate at 1 AU needed to account for the nonadiabatic solar wind expansion. The results suggest that the reduction in turbulent heating in high cross helicity flows creates a tangible deficit in the heating rate required by empirical models based on average solar wind properties.

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