Polar coronal jets

We present ultraviolet spectroscopy of polar coronal jets obtained with the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory. They correlate with the Extreme—Ultraviolet Imaging Telescope Fe XII (195Å) and Large Angle Spectrometric Coronagraph white—light jet events. We found that the jets typically undergo two phases: at the first phase the O VI lines show a brief intensity enhancement and narrowing, while the H I Lyα line is not enhanced, and the second phase, about 25 minutes later, when the H I Lyα line shows maximum intensity enhancement and narrowing, while the O VI line is relatively unchanged. We modeled the observable properties of the jets from 1997 August 5, detected at 1.71 R ⊙. We interpret the first phase as the fast, dense centroid of the jet passing by the slit, and the second phase as a passage of cooler, lower density material following the centroid. Possible scenarios of the electron temperature variations needed to account for observed conditions on 1997 August 5 indicate that some heating is required. We computed models of the temperature and nonequilibrium ionization state of an expanding plasma using various forms for the heating rates. We discuss the model results and estimate the initial electron temperature and heating rate required to reproduce the observed O VI ionization state. We also place some constraints on the origin of the jet material based on the inferred plasma properties.