Parker Solar Probe Enters the Magnetically Dominated Solar Corona

An Extended and Fragmented Alfvén Zone in the Young Solar Wind

“…For details on the processing of PSP measurements see Bandyopadhyay et al (2022). It is apparent that the Alfvén Mach number dips below unity several times in this period; these are the first sub-Alfvénic periods observed by PSP, as reported by Kasper et al (2021) and further analyzed by Bandyopadhyay et al (2022). The agreement is again rather good considering that the phases of the fluctuations are random, and only the local variances are meaningful.…”

“…Remote sensing observations (Lotova et al 1985;Lotova 1988) indicate a range of distances in which a critical transition might occur. Recent detections of sub-Alfvénic regions near PSP perihelia also indicate a possible range of distances associated with the transition (Kasper et al 2021). Predictions of ranges of distances also have been reported based on extrapolation of in-situ measurements (Goelzer et al 2014;Kasper & Klein 2019;Wexler et al 2021).…”

“…The first passages of PSP into the sub-Alfvénic region have comprised several time periods, the longest of which is a few hours (Kasper et al 2021). Further observations in more persistent sub-Alfvénic wind will be required for confirmation of these early measurements.…”

“…This has enabled the first glimpse of the magnetically dominated coronal plasma using in situ observations. The leading order expectations of distinctive features of coronal plasma and electromagnetic fields thus far appear to be intact (Kasper et al 2021;Bandyopadhyay et al 2022). In the present paper we explore how subsequent passages through this sub-Alfvénic coronal plasma might look in subsequent PSP orbits if, indeed, the trans-Alfvénic boundary is a zone rather than a well-defined surface.…”

“…Indeed, the crucial processes that heat the corona and accelerate the wind originate in the magnetically dominated region, thus providing a fundamental physics motivation for ★ E-mail: rohitc@udel.edu the PSP mission (Fox et al 2016). Recently, on its eighth perihelion, at a distance of about 19 R , PSP passed into sub-Alfvénic plasma for extended periods for the first time (Kasper et al 2021). This has enabled the first glimpse of the magnetically dominated coronal plasma using in situ observations.…”