Abstract
We have studied the radio properties of 18 X-ray coronal jets (observed by the Yohkoh SXT) using Nobeyama 17
GHz data. We also searched for chromospheric ejecta (Hα surges) during the time intervals that the X-ray
images were available. Microwave emission was associated with the majority of the X-ray jets. The radio emission
came from the base or the lower part of the jets. We detected radio emission from almost all jets which showed
flare-like activity at their footpoints. The 17 GHz time profiles were gradual and unpolarized, implying that the
emission was thermal. When possible, we computed the physical properties of the X-ray-emitting ejected plasma.
In one two-sided-loop type jet and one anemone-type jet, the observed microwave fluxes from the lower part of the
jets were well above the fluxes predicted from the computed electron temperatures and emission measures of the soft
X-ray-emitting material on the basis of thermal free-free emission. We interpreted the large discrepancies in terms
of the presence of lower temperature material which cannot be detected by the SXT but produces strong microwave
free-free emission. This is the first time that such material is observed in two-sided-loop type jets. Thus our
observations confirm the theoretical prediction by Yokoyama and Shibata (1996). We detected no cool material at the
base of the jets. We also observed an Hα surge which was not associated with an X-ray jet and showed no
signatures on the SXT images but was detected with the Nobeyama Radioheliograph. The emission of the microwave
surge-associated source was free-free from the chromospheric plasma. Constraints for the surge density were
derived.