Formation of Chromospheric Spicules in Magnetic Bright Points: An Analytical Approach Using Cartesian Slab Geometry

Abstract

We aim to provide insight into chromospheric spicules by suggesting a new formation mechanism. A magnetic field boundary condition is imposed, generating an Alfvén wave that shears a magnetic slab and propagates up the slab. The resulting Lorentz force accelerates material vertically, potentially nonlinearly driving a jet-like feature. This formation mechanism is applied to take place in a magnetic bright point embedded in the photosphere, providing motivation to use the simplifying assumption of a zero-β plasma. After deriving an analytical expression describing the vertical mass flux that constitutes the spicular jet, further understanding is gained by examining a model example of a magnetic field boundary condition in terms of standard functions. By visualizing the vertical mass flux through 3D plots, we demonstrate that the jet properties capture the observed properties of chromospheric spicules during their formation. This vindicates the model and simplifying assumptions used. Although we do not provide insight into the full evolution of a spicule, we show that the role of Alfvén waves triggered by shear in fact could be a viable formation mechanism for at least some chromospheric spicules. Consequently, we provide a starting point for further studies of this formation mechanism, which will lead to a greater understanding of the vast variety of chromospheric jets.

Could Switchbacks Originate in the Lower Solar Atmosphere? II. Propagation of Switchbacks in the Solar Corona

“…The mass flow along the propagation direction of the switchback is due to the vertical component of the velocity perturbation, and not due to magnetic pressure gradients, as in the case of ponderomotive forces (Hollweg 1971;Chen & Hasegawa 1974), the magnetic field magnitude being constant. Nevertheless, the discussion above on gravitational damping should apply also for non-circularly polarized waves which lift mass ponderomotively (e.g., Oxley et al 2020). While ponderomotive forces are present irrespective of gravitational stratification, in the case of the propagating Alfvénic switchback there are essentially no density perturbations without gravity.…”

Quasi-periodic spicule-like cool jets driven by Alfvén pulses

“…Kudoh & Shibata (1999) have also studied the evolution of spicules due to Alfvén waves. Oxley et al (2020) provide the analytical model for the generation of spicule-like jets due to the tension component of the Lorentz force. Nishizuka et al (2008) have given the physical scenario of the formation of longer chromospheric jets due to Lorentz force and Alfvén perturbations at their base.…”

Modeling solar chromospheric spicules with intense lasers

“…There has been no conclusive explanation of the spicules since their discoveries in 1877. Many models have been proposed based on the source of energy driving the ejection of spicules from the chromosphere [10], including the strong pulse model [11,12], the rebound shock model [13], the Alfv en wave model [14][15][16][17][18][19][20] and the magnetic reconnection model [9,21]. Dey et al discussed the similarities between spicules observed on the Sun and jets produced by polymeric fluids.…”