What is a Macrospicule?

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 304Å 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 −1 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 10 ± 2 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.

Estimating the Temperature and Density of a Spicule from 100 GHz Data Obtained with ALMA

“…Therefore, it is appropriate to compare our results with the properties of macrospicules, rather than those of spicules. Macrospicules are most often visible in EUV transitionregion lines, such as in He II 304Å, and consist of a cool core and hot sheath (e.g., Bohlin et al 1975;Withbroe et al 1976;Parenti et al 2002;Loboda & Bogachev 2019). Since the Mg II/304Å spicule has a cool component revealed in the Mg II image and a hotter component shown in the He II 304Å images, it has the typical properties of macrospicules described in the preceding papers.…”

The Solar Orbiter mission

“…In fact, the fast wind, which does not exhibit strong FIP enhancements, could come directly from the photosphere, from small, cool coronal loops and open magnetic funnels at the base of coronal holes or spicules, which also exhibit small FIP enhancements. Remote observations have revealed many cases of macrospicules undergoing reconnection and erupting within coronal holes (Loboda & Bogachev 2019). Do they contribute to the fast solar wind streams?…”

Numerical simulations of macrospicule jets under energy imbalance conditions in the solar atmosphere

“…We use a higher velocity pulse to excite a faster jet and not let dissipation or numerical reflections dominate the system's evolution on timescales of interest and minimize numerical issues. Also, the initial amplitude of 100 km s −1 is the range of the average initial velocities from 70 to 140 km s −1 estimated by Loboda & Bogachev (2019) through a statistical analysis of macrospicule jets observed in coronal-holes and the quiet Sun.…”

“…These giant spicules were introduced by Bohlin et al (1975), concerning the jets observed in Skylab's extreme ultraviolet (EUV) spectroheliograms at the solar limb. Besides, they are observed in polar coronal holes, where they reach heights from 7 to 70 Mm above the solar limb, maximum velocities from 10 to 150 km s −1 and lifetimes ranging from 3 to 45 minutes (Bohlin et al 1975;Withbroe et al 1976;Dere et al 1989;Karovska & Habbal 1994;Parenti, S. et al 2002;Bennett & Erdélyi 2015;Kiss et al 2017;Sterling 2000;Wilhelm 2000;Loboda & Bogachev 2019). In this context, a number of mechanisms have been proposed for the formation of macrospicules, for instance, by a pressure pulse (Hollweg 1982), through a velocity pulse (Suematsu et al 1982;Murawski et al 2011), magnetic recconection (Shibata 1982); among others (Moore et al 1977;De Pontieu et al 2004;Kamio et al 2010).…”