How Alfv\'en waves energize the solar wind: heat vs work

2021 
A growing body of evidence suggests that the solar wind is powered to a large extent by an Alfven-wave (AW) energy flux. AWs energize the solar wind via two mechanisms: heating and work. We use high-resolution direct numerical simulations of reflection-driven AW turbulence (RDAWT) in a fast-solar-wind stream emanating from a coronal hole to investigate both mechanisms. In particular, we compute the fraction of the AW power at the coronal base ($P_{\rm AWb}$) that is transferred to solar-wind particles via heating between the coronal base and heliocentric distance $r$, which we denote $\chi_{\rm H}(r)$, and the fraction that is transferred via work, which we denote $\chi_{\rm W}(r)$. We find that $\chi_{\rm W}(r_{\rm A})$ ranges from 0.15 to 0.3, where $r_{\rm A}$ is the Alfven critical point. This value is small compared to~one because the Alfven speed $v_{\rm A} $ exceeds the outflow velocity $U$ at $r r_{\rm A}$, where $v_{\rm A} r_{\rm A}$ is a modest fraction of $P_{\rm AWb}$. We find that heating is more effective than work at $r
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