Solar Origin of Compressive Alfvénic Spikes/Kinks as Observed by Parker Solar Probe

Abstract

The solar wind is found by the Parker Solar Probe to be abundant with Alfvénic velocity spikes and magnetic field kinks. Temperature enhancement is another remarkable feature associated with the Alfvénic spikes. How the prototype of these coincident phenomena is generated intermittently in the source region is an important and wide-ranging subject. Here we propose a new model introducing guide-field discontinuity into the interchange magnetic reconnection between open funnels and closed loops with different magnetic helicities. The modified interchange reconnection model not only can accelerate jet flows from the newly opening closed loop but also can excite and launch Alfvénic wave pulses along the newly reconnected and post-reconnected open flux tubes. We find that the modeling results can reproduce the following observational features: (1) Alfvén disturbance is pulsive in time and asymmetric in space; (2) Alfvénic pulse is compressive with temperature enhancement and density variation inside the pulse. We point out that three physical processes co-happening with Alfvén wave propagation can be responsible for the temperature enhancement: (a) convection of heated jet flow plasmas (decrease in density), (b) propagation of compressive slow-mode waves (increase in density), and (c) conduction of heat flux (weak change in density). We also suggest that the radial nonlinear evolution of the Alfvénic pulses should be taken into account to explain the formation of magnetic switchback geometry.

Growth of Outward Propagating Fast-Magnetosonic/Whistler Waves in the Inner Heliosphere Observed by Parker Solar Probe

“…This work addresses the issue of the origin of kinetic waves in the inner heliosphere. We point out that kinetic waves are not necessarily created in the solar wind source region, though some proportion of waves may be launched from the solar atmosphere through magnetic reconnection or turbulent advection shaking (He et al 2021; 2020). Instead they can be locally excited and grow due to instability in the inner heliosphere.…”

“…There are two different views on this issue. (1) One view is that the wave fluctuations are emitted from the solar atmosphere and cascade from the MHD scales to the kinetic scales during their journey of outward propagation (He et al 2009;Cranmer et al 2015;Yang et al 2017;Chandran & Perez 2019;He et al 2021). (2) The other view is that the kinetic-scale waves are produced locally in the interplanetary space due to some plasma instability (Jian et al 2014;Wicks et al 2016;Jiansen et al 2018;Zhao et al 2019;Verniero et al 2020).…”

Oscillatory Reconnection of a 2D X-point in a hot coronal plasma

“…Oscillatory reconnection may also be a possible explanation of phenomena now being observed by the Parker Solar Probe (e.g. Bale et al 2016Bale et al , 2019Kasper et al 2019) including Alfvénic spikes/kinks (He et al 2021) and periodicities correlated with Type III radio bursts (Cattell et al 2021).…”

On the properties of Alfvénic switchbacks in the expanding solar wind: the influence of the Parker spiral

“…Later in this work, we examine the properties of solutions to Eqs. (7) and ( 8) by means of its numerical solution. For this, we use a standard Fourier pseudospectral method with fourth-and fifth-order Runga-Kutta timestepping and 1024 grid points in λ .…”

“…As such, a range of different explanations have been put forth for their origin, each relating in some way to fundamental low-coronal or solar-wind physics with the switchbacks emerging as an observable consequence. These explanations include models relating to interchange reconnection near the solar surface [4][5][6][7], low-coronal jets or other motions [8,9], field-line folding due to asymmetries from interchange reconnection [10], instabilities between different wind streams [11], or the growth of Alfvénic fluctuations due to plasma expansion [12][13][14]. Given these widely differing ideas, each of which provide different predictions for switchback properties and occurrence rate, a clear path forward to bettering our understanding of the solar wind presents itself: quantify various (hopefully) unique and observationally testable predictions for each model, then compare these to observations.…”