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High-resolution temporal series of monochromatic full-Sun images in the L Mg XII emission line at 8.42Å have been obtained by the SPectroheliographIc X-Ray Imaging Telescope (SPIRIT) spectroheliograph on the CORONAS-F satellite. For a six-month period since the launch on 2001 July 31 more than 10 000 Mg XII images were recorded. The images revealed plasma structures with the temperature in the range 3-20 MK characterized by specific shape and dynamics, different to that of relatively low temperature (1-2 MK) plasma. The main remarkable features of the phenomena first seen in the monochromatic images are as follows:(1) high spatial variability in brightness with the contrast of more than two orders of magnitude, (2) the presence of some compact sources with high altitude locations up to 0.3 solar radius and well-distinguished 'spider'-like forms, (3) substantially different variability in dynamical behaviour characterized by lifetimes from minutes to days. Sporadic condensations of coronal plasma with log N e ≈ 10 and peak temperature of about 10 MK were observed in the vicinity of active region systems.

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The intensity ratio of the components of the Mg xn 8.42 ~ (ls 2S1/2 -2p 2P1/2. 3/2) doublet in solar flare spectra has been investigated using observations recorded from the Intercosmos 7 satellite. The observed values of the ratio fall within the interval 0.38-0.66 and have been compared with recent theoretical predictions based on an optically thin collisional-radiative model. It has been found that for the flare plasma the low values of the ratio cannot be explained since they fall below the smallest theoretical value. The highest values on the other hand require that an unacceptably high electron density be postulated. It is suggested that both high and low values may be caused by the resonance line scattering of the Mg xH quanta in the flare volume, provided that the volume is elongated and not spherical.The intensity of the nearby satellite lines is also investigated. Good agreement between the theoretical and observed intensities is found.