FINE-STRUCTURE OF THE X-RAY AND RADIO EMISSIONS OF THE QUIET SOLAR CORONA

Two deep soft X-ray exposures of a quiet region on the Sun were made w ith the SXT telescope on board the Yohkoh satellite on 20 Feb 1995. We report on the spatial X-ray fine structure. Regions of enhanced X-ray emission, more than two orders of magnitude fainter than previously r eported X-ray bright points, are loosely associated with bipolar regio ns in the magnetic network. The power spectrum of quiet X-ray images a t small spatial scares is similar to that of active regions, but exhib its a kink at a scale of approximate to 25, 000 km, possibly connected to the supergranular structure. The spatial X-ray structures in the t ime averaged image amount to an rms amplitude which is 6% of the mean value. The X-ray structures correlate with contemporaneous radio maps obtained by the VLA at wavelengths of 1.3, 2.0, and 3.6 cm. The amplit ude of the brightness variations in the images increases with radio wa velength, i.e., with increasing height. The cross-correlation coeffici ent with the absolute magnetic field strength, however, generally decr eases with height, consistent with the idea of bipolar regions in the network and of the magnetic field deviating from vertical in the upper chromosphere. The X-ray observations require an enhanced pressure in the corona above the magnetic network, but suggest similar temperature s. Model calculations show that, under a constant temperature, an rms density increase (relative to that in the cell interior) ranging from about 20% in the chromosphere to 60% in the low corona is sufficient t o explain the observed standard deviations due to the spatial structur es in radio waves and soft X-rays, respectively.