Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere

Abstract

Context. Switchbacks are discrete angular deflections in the solar wind magnetic field that have been observed throughout the heliosphere. Recent observations by Parker Solar Probe (PSP) have revealed the presence of patches of switchbacks on the scale of hours to days, separated by 'quieter' radial fields. Aims. We aim to further diagnose the origin of these patches using measurements of proton temperature anisotropy that can illuminate possible links to formation processes in the solar corona. Methods. We fitted 3D bi-Maxwellian functions to the core of proton velocity distributions measured by the SPAN-Ai instrument onboard PSP to obtain the proton parallel, T p, , and perpendicular, T p,⊥ , temperature. Results. We show that the presence of patches is highlighted by a transverse deflection in the flow and magnetic field away from the radial direction. These deflections are correlated with enhancements in T p, , while T p,⊥ remains relatively constant. Patches sometimes exhibit small proton and electron density enhancements. Conclusions. We interpret that patches are not simply a group of switchbacks, but rather switchbacks are embedded within a largerscale structure identified by enhanced T p, that is distinct from the surrounding solar wind. We suggest that these observations are consistent with formation by reconnection-associated mechanisms in the corona.

Turbulent generation of magnetic switchbacks in the Alfvénic solar wind

“…The proton core parallel temperature is found to be constant across switchbacks (Woolley et al 2020), possibly because switchbacks move through the plasma at the local Alfvén speed, which prevents them from strongly heating any particular parcel of plasma before propagating past it. We note, however, that the active phase mentioned above is characterized by an enhanced proton parallel temperature (Woodham et al 2020).…”

“…Besides increasing the numerical resolution, there are a number of other ways that the simulation presented here could be further improved. Since an artificial energy source term is used, our model does not accurately capture the thermodynamic properties of switchbacks (Woolley et al 2020;Woodham et al 2020). Field-aligned thermal conduction needs to be considered in the future, ideally incorporating the deviation from the Spitzer-Härm heat flux in the weakly collisional, large-Knudsen-number regime (Salem et al 2003;Bale et al 2013;Verscharen et al 2019).…”

Multiscale Solar Wind Turbulence Properties inside and near Switchbacks measured by Parker Solar Probe

“…These first results provided an overview of SB properties, finding some differences compared to previous reports. Most notably, PSP did not observe SBs as isolated events, but rather 'clustered' phenomena (Dudok de Wit et al 2020), with measured parallel temperature changing as the spacecraft moves through the cluster (Woodham et al 2020). This claim is supported by two independent arguments: 1) normalized magnetic field deflections from the Parker spiral (scaled to values between 0 and 1 depending on cosine value) exhibit a power law distribution, which is a property related to phenomena such as entangled filaments and flux tubes, rather than a Gaussian distribution, which would represent randomized events; and 2) Detrended Fluctuation Analysis (Kantelhardt et al 2001) shows an increase in long range correlations in time series for SBs compared to quiescent intervals.…”