Present state of X-ray investigations of non-flaring actlve regions is briefly revlewed, It is stressed that it Is very Important to háve simultaneous records of high-quality X-ray spectra and high resolutlon X-ray images. The spectra allow to derive reliahle temperature distrlbutions (differential emission measure) of the coronal plasma. When combined with the X-ray images, it allows to investigate the rate and spatial distrlbution of the energy release (heating of the active region corona), Thls, In tum, provides an important possibiility to test empirically the theories of actlve region heating. These large potential possibillties of active region investigatlon are far from being exhausted and they should be used more efficiently in future Investigations.
We have analysed the relations between basic physical parameters In the flarlng loops. Based on the results of the "Palermo Code" hydrodynamlc flare modellng, we have checked that even for transient energy Input, the energy deposltlon rate can be adequately expressed In terms of the actual maximum temperature of the plasma in the loop. Taklng thls Into account, we have used a slmple equatlon governlng the energy balance In the flarlng loop. Thls
equation relates the basic characterlstlcs such as: the maximum temperature, the mean temperature and the emlsslon measure wlth the loop's length and cross-sectlon as the parameters. Except the geometry parameters, the other characterlstics can be determined based on the soft X-ray spectral analysis. In the paper, we describe the diagnostic procedure called LEBAN which may be helpful In deriving basic geometrlcal loop parameters. Palermo model calculations have been used to test reliabillity of the procedure.
Summary: In the present paper indications have been presented that:
(1) Kernels with tangled magnetic lines of force occur in solar flares.
(2) Random (turbulent) motions occur in hot flare plasma.
(3) A MHD turbulence can explain huge flare energy release (plasma heating. electron and proton acceleration).
(4) It has been also shown that a MHD turbulence can efficiently develop in a strong magnetic field in the solar corona.
On this basis it is suggested that the MHD turbulence is Ihe basic mechanism of the flare energy release.