Energy transfer, discontinuities and heating in the inner solar wind measured with a weak and local formulation of the Politano-Pouquet law

Abstract

The solar wind is a highly turbulent plasma for which the mean rate of energy transfer $\epsilon$ has been measured for a long time using the Politano-Pouquet (PP98) exact law. However, this law assumes statistical homogeneity that can be violated by the presence of discontinuities. Here, we introduce a new method based on the inertial dissipation $\Dis$ whose analytical form is derived from incompressible magnetohydrodynamics (MHD); it can be considered as a weak and {\it local} (in space) formulation of the PP98 law whose expression is recovered after integration is space. We used $\Dis$ to estimate the local energy transfer rate from the \textit{THEMIS-B} and \textit{Parker Solar Probe} (PSP) data taken in the solar wind at different heliospheric distances. Our study reveals that discontinuities near the Sun lead to a strong energy transfer that affects a wide range of scales $\sigma$. We also observe that switchbacks seem to be characterized by a singular behavior with an energy transfer varying as ${\sigma }^{-3/4}$, which slightly differs from classical discontinuities characterized by a ${\sigma }^{-1}$ scaling. A comparison between the measurements of $\epsilon$ and $\Dis$ shows that in general the latter is significantly larger than the former.

13 pages, 9 figures, submitted to The Astrophysical Journal

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