What Determines the Height of Spicules?
We perform numerical simulations for torsional Alfvén waves and slow waves propagating along an open magnetic flux tube in the solar atmosphere to elucidate the mechanisms of spicule formation and coronal heating. We introduce random motions of about 1 km s-1 in the photosphere as the source of Alfvén and slow waves, and solve the 1.5-dimensional magnetohydrodynamic equations. The waves generated by the random motions propagate upward and lift up the transition region. The chromospheric plasma just below the transition region is thought to be observed as a spicule. We investigate the effect of the initial height of the transition region, or transition-region pressure, on spicule formation. Our results agree well with the observational fact that spicules are absent over plages, where the transition-region pressure is high, and tall under coronal holes, where the transition-region pressure is low. We also show that the dependence of spicule height on the initial transition-region height
