Statistical Study of Solar X-Ray Jets Observed with the Yohkoh Soft X-Ray Telescope

We have found 100 X-ray jets in the database of full Sun images taken with the Soft X-ray Telescope (SXT) aboard Yohkoh during the period from 1991 November through 1992 April. A statistical study for these jets results in the following characteristics: 1) Most are associated with small flares (microflaressubflares) at their footpoints. 2) The lengths lie in the range of a few x 10-4 x 10 km. 3) The widths are 5 x 10-10 km. 4) The apparent velocities are 10-1000 km s 1 with an average velocity of about 200 km s _ 1 . 5) The lifetime of the jet extends to ~ 10 hours and the distribution of the observed lifetime is a power law with an index of ~ 1.2. 6) 76% of the jets show constant or converging shapes; the width of the jet is constant or decreases with distance from the foot point. The converging type tends to be generated with an energetic foot point event and the constant type by a wide energy range of the footpoint event. 7) Many jets (~ 68%) appear in or near to active regions (AR). Among the jets ejected from bright-point like features in ARs, most (~ 86%) are observed to the west of the active region. 8) 27% of the jets show a gap ( > 10 km) between the exact footpoint of the jet and the brightest part of the associated flare. 9) The X-ray intensity distribution along an X-ray jet often shows an exponential decrease with distance from the footpoint. This exponential intensity distribution holds from the early phase to the decay phase.