A New Type of Jet in a Polar Limb of the Solar Coronal Hole

Abstract

A new type of chromospheric jet in a polar limb of a coronal hole is discovered in the Ca ii filtergram of the Solar Optical Telescope on board the Hinode. We identify 30 jets in a filtered Ca ii movie with a duration of 53 minutes. The average speed at their maximum heights is found to be 132 ± 44 km s−1 ranging from 57 to 264 km s−1 along the propagation direction. The average lifetime is 20 ± 6 ranging from 11 to 36 s. The speed and lifetime of the jets are located at end-tails of those parameters determined for type II spicules, hence implying a new type of jets. To confirm whether these jets are different from conventional spicules, we construct a time–height image averaged over a horizontal region of 1″, and calculate lagged cross-correlations of intensity profiles at each height with the intensity at 2 Mm. From this, we obtain a cross-correlation map as a function of lag and height. We find that the correlation curve as a function of lag time is well fitted into three different Gaussian functions whose standard deviations of the lag time are 193, 42, and 17 s. The corresponding propagation speeds are calculated to be 9 km s−1, 67 km s−1, and 121 km s−1, respectively. The kinematic properties of the former two components seem to correspond to the 3-minute oscillations and type II spicules, while the latter component to the jets is addressed in this study.

Rapid Evolution of Type II Spicules Observed in Goode Solar Telescope On-disk Hα Images

“…Recently Cho et al (2019) reported on a new type of faint chromospheric jets detected at a limb in Ca II Hinode images. These jets exhibit an average speed of about 132 km s −1 and an average lifetime of 20 s, ranging from 11 to 36 s. These new limb jets could be related to the short lived RBEs discussed here.…”

The Solar Orbiter mission

“…Polar coronal holes have been intensively studied from the ecliptic plane (e.g. Chandrashekhar et al 2014;Gupta 2014;Spadaro et al 2017;Hahn et al 2018;Cho et al 2019;Tei et al 2020;Peleikis et al 2017;), but lack of imaging from outside the ecliptic has so far limited our understanding of the geometry of polar structures. As described in Section 2.2.2, the magnetic flux in the heliosphere varies with the solar cycle.…”