Abstract
If MHD turbulence is a dominant process acting in the solar wind between the Sun and 1 AU, then the destruction and regeneration of structure in the solar-wind plasma is expected. Six types of solar-wind structure at 1 AU that are not destroyed by turbulence are examined: 1) corotating-interaction-region stream interfaces, 2) periodic density structures, 3) magnetic structure anisotropy, 4) ion-composition boundaries and their co-located current sheets, 5) strahl-intensity boundaries and their co-located current sheets, and 6) non-evolving Alfvénic magnetic structure. Implications for the solar wind and for turbulence in the solar wind are highlighted and a call for critical future solar-wind measurements is given.
Highlights
Turbulence in the solar wind should have multiple impacts on the plasma and magnetic structure between the Sun and 1 AU: heating of the particle populations, mixing, flux-tube shredding, destruction of structure from the Sun, and a constant annihilation and recreation of its own structures.The quasi-two-dimensional component of MHD turbulence is eddy like in its fluid motion and it is anticipated that this will give rise to eddy transport in the plasma (Matthaeus et al, 1995; Pucci et al, 2016)
Searches for proton heating at solar-wind current sheets (Borovsky and Denton, 2011) and at solar-wind velocity shears (Borovsky and Steinberg, 2014), as measured by an increase in the proton specific entropy, found no evidence for localized heating. (Note that this result is contradicted by studies using the proton temperature instead of entropy as an indication for localized heating (Osman et al, 2011, 2012; Wang et al, 2013)) 3) For an MHD-turbulence energy cascade to occur, the presence of both inward and outward propagating Alfvén waves must be present (Verdini et al, 2009; Perez and Boldyrev, 2010; Stawarz et al, 2010), with the amplitudes of the inward waves characterized by the inward Elsasser variable Zin
A question to consider is: If solar-wind turbulence id driven by large-scale shears in the solar wind (Bavassano and Bruno, 1989; Roberts et al, 1992; Goldstein et al, 1995) why do these classic prominent shears survive to 1 AU? Note that an argument the shear is thinning because of compression is probably invalid since 1) it will be shown later that the corotating interaction region (CIR) volume compression is only about a factor of 2 and 2) the net expansion of the solar wind still overpowers the CIR compression of the solarwind plasma
Summary
Turbulence in the solar wind should have multiple impacts on the plasma and magnetic structure between the Sun and 1 AU: heating of the particle populations, mixing (chunk-size evolution followed by homogenization), flux-tube shredding, destruction of structure from the Sun, and a constant annihilation and recreation of its own structures. (Note that this result is contradicted by studies using the proton temperature instead of entropy as an indication for localized heating (Osman et al, 2011, 2012; Wang et al, 2013)) 3) For an MHD-turbulence energy cascade to occur, the presence of both inward and outward propagating Alfvén waves must be present (Verdini et al, 2009; Perez and Boldyrev, 2010; Stawarz et al, 2010), with the amplitudes of the inward waves characterized by the inward Elsasser variable Zin. The solar-wind data analysis of Wang et al (2018) finds that two dominant sources of Zin in solar-wind measurements are 1) measurement noise and 2) non-propagating convective structures in the plasma.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
