On the role of spicules in solar coronal emission

The advent of high-resolution imaging and spectroscopic observations has paved the path to revisit the role of spicules in explaining the hot solar corona. Some of the studies suggest that spicules commonly categorized as type II play an important role in providing mass and energy to the solar corona. In this work, we test the hypothesis that the hot material at the tip of the spicule can solely explain the hot mass and hence the emission in the solar corona. Our numerical model mimics the propagation of a spicule with a hot tip followed by a cold body in a warm loop with apex temperature 0.5 MK. To cover the vast range of observed spicules, spicules with varying tip temperatures are injected into the loop at various speeds. Depending on the tip temperature and injected spicule speed, such injections result in the generation of piston- and pressure-driven shocks. In the absence of any external heating, the hot material at the spicule tip cools rapidly and disappears from coronal lines like Fe XII (195 Å) and Fe XIV (274 Å). Consequently, most of the overall hot emission from the loop comes from pre-existing coronal material that is heated by the shock and by thermal conduction from the shock. However, the synthetic spectral lines show strong discrepancies with observations, both in shape and Doppler shift. In addition, the spatially and temporally averaged intensities are found to be extremely faint, pointing to the need for one to several orders of magnitude more spicules than reported in the literature to account for the coronal emission. Our findings only apply to the hot material at the spicule tip. Waves or currents which may get generated during spicule ejection process can lead to coronal heating and may explain some nonspicular loops. However, it is still doubtful whether it can explain the many nonspicular loops as inferred by observed line profile asymmetries.