A New Type of Jets in a Polar Limb of Solar Coronal Hole

Abstract

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

21 pages, 33 figures, published in ApJ Letters

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