Notice:

How Alfvén waves energize the solar wind: heat versus work
Author  Perez, Jean; Chandran, Benjamin; Klein, Kristopher; Martinovic, Mihailo; 
Keywords  Parker Data Used; astrophysical plasmas; space plasma physics; plasma nonlinear phenomena; Astrophysics  Solar and Stellar Astrophysics; Physics  Plasma Physics; Physics  Space Physics 
Abstract  A growing body of evidence suggests that the solar wind is powered to a large extent by an Alfvénwave (AW) energy flux. AWs energize the solar wind via two mechanisms: heating and work. We use highresolution direct numerical simulations of reflectiondriven AW turbulence (RDAWT) in a fastsolarwind stream emanating from a coronal hole to investigate both mechanisms. In particular, we compute the fraction of the AW power at the coronal base ($P_\textrm AWb$) that is transferred to solarwind particles via heating between the coronal base and heliocentric distance $r$, which we denote by $χ _{H}(r)$, and the fraction that is transferred via work, which we denote by $χ _{W}(r)$. We find that $χ _{W}(r_{A})$ ranges from 0.15 to 0.3, where $r_{A}$ is the Alfvén critical point. This value is small compared with one because the Alfvén speed $v_{A}$ exceeds the outflow velocity $U$ at $r < r_{A}$, so the AWs race through the plasma without doing much work. At $r>r_{A}$, where $v_{A} < U$, the AWs are in an approximate sense stuck to the plasma , which helps them do pressure work as the plasma expands. However, much of the AW power has dissipated by the time the AWs reach $r=r_{A}$, so the total rate at which AWs do work on the plasma at $r>r_{A}$ is a modest fraction of $P_\textrm AWb$. We find that heating is more effective than work at $r < r_{A}$, with $χ _{H}(r_{A})$ ranging from 0.5 to 0.7. The reason that $χ _{H} ≥ 0.5$ in our simulations is that an appreciable fraction of the local AW power dissipates within each Alfvénspeed scale height in RDAWT, and there are a few Alfvénspeed scale heights between the coronal base and $r_{A}$. A given amount of heating produces more magnetic moment in regions of weaker magnetic field. Thus, paradoxically, the average proton magnetic moment increases robustly with increasing $r$ at $r>r_{A}$, even though the total rate at which AW energy is transferred to particles at $r>r_{A}$ is a small fraction of $P_\textrm AWb$. 
Year of Publication  2021 
Journal  Journal of Plasma Physics 
Volume  87 
Number of Pages  905870218 
Section  
Date Published  04/2021 
ISBN  
URL  https://ui.adsabs.harvard.edu/abs/2021JPlPh..87b9018P 
DOI  10.1017/S0022377821000167 