Multialtitude Observations of a Coronal Jet during the Third Whole Sun Month Campaign

Abstract

On 1999 August 26, a coronal jet occurred at the northwest limb near a sigmoid active region (AR 8668) that was the target for a joint observation plan (SOHO joint observing program 106) during the third Whole Sun Month Campaign. This jet was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT, TRACE, and Mauna Loa Solar Observatory CHIP and PICS) and at 1.64 R☉ (SOHO/UVCS). At the limb, this jet event displayed both low- and high-temperature components. Both high- and low-temperature components were evident during the early phase (first 20 minutes) of the event. However, the low-temperature component is maintained for ~1 hr after the higher temperature component is gone. There is a second brightening (a possible second jet) seen by EIT and TRACE about 50 minutes after the onset of the first jet. The line-of-sight motion at the limb began with a 300 km s-1 redshift and evolved to a 200 km s-1 blueshift. At 1.64 R☉, the intensities of Lyα and Lyβ in the jet increased by a factor of several hundred compared with the background corona. The C III λ977 line also brightened significantly. This indicates low-temperature [~(1-2) × 105 K] emission in the jet, while the intensities of O VI λ1032 and O VI λ1037 increased by as much as a factor of 8. The UVCS data show evidence of heating at the early phase of the event. The Doppler shift in the lines indicates that the line-of-sight (LOS) velocity in the jet started from ~150 km s-1 in blueshift and ended at ~100 km s-1 in redshift. This LOS motion seen at 1.64 R☉ was apparently opposite to what was observed when the jet emerged from the limb. The Doppler dimming analysis indicates that the radial outflow speed correlates with the magnitude of the LOS speed. Interestingly, UVCS observations at 2.33 and 2.66 R☉ show no trace of the jet and SOHO/LASCO observations also yield no firm detection. We find that a simple ballistic model can explain most of the dynamical properties of this jet, while the morphology and the thermal properties agree well with reconnection-driven X-ray jet models.