paper

What is a Macrospicule?

arXiv:1902.01380 · doi:10.3847/1538-4357/aafa7a

Abstract

Macrospicules are typically described as solar jets that are larger and longer-lived than spicules, and visible mostly in transition-region spectral lines. They show a broad variation in properties, which pose substantial difficulties for their identification, modelling, and the understanding of their role in the mass and energy balance of the solar atmosphere. In this study, we focused on a sub-population of these jets that undergo parabolic trajectories when observed in the He II 304 Å line using high-cadence observations of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) to accumulate a statistically significant sample, which included 330 such events. We found these jets to be typically narrow (3-6 Mm), collimated flows of plasma, which reach heights of about 25 Mm, thus being among the smallest jets observed in the extreme ultraviolet (EUV). Combined with the rise velocities of 70-140 km/s and lifetimes of around 15 min, this makes them plausible candidates for the EUV counterpart of type II spicules. Moreover, we have found their dynamics to be inconsistent with a purely ballistic motion; instead, there is a strong correlation between the initial velocities and decelerations of the jets, which indicates that they may be driven by magneto-acoustic shocks with a dominant period of 102 min. This makes these EUV jets similar in their dynamics to the conventional, or type I spicules, thus justifying the name of macro-spicules in this case, while a substantial difference in the shock periods (1-2 min for the chromospheric jets) suggests a dissimilarity in the formation conditions.

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