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

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.