A Study of Polar Jet Parameters Based on Hinode XRT Observations

Abstract

Hinode/SOHO campaign 7197 is the most extensive study of polar jet formation and evolution from within both the north and south polar coronal holes so far. For the first time, this study showed that the appearance of X-ray jets in the solar coronal holes occurs at very high frequency - about 60 jets d^-1 on average. Using observations collected by the X-Ray Telescope on Hinode, a number of physical parameters from a large sample of jets were statistically studied. We measured the apparent outward velocity, the height, the width and the lifetime of the jets. In our sample, all of these parameters show peaked distributions with maxima at 160kms^-1 for the outward velocity, 5 × 10⁴ km for the height, 8 × 10³ km for the width, and about 10min for the lifetime of the jets. We also present the first statistical study of jet transverse motions, which obtained transverse velocities of 0-35kms^-1. These values were obtained on the basis of a larger (in terms of frequency) and better sampled set of events than what was previously statistically studied (Shimojo et al. 1996, PASJ, 48, 123). The results were made possible by the unique characteristics of XRT. We describe the methods used to determine the characteristics and set some future goals. We also show that despite some possible selection effects, jets preferably occur inside the polar coronal holes.