The analysis of hard X-ray radiation of flares with occulted footpoints

14 behind-the-limb flares with occulted footpoints, well-observed by Yohkoh , have been carefully selected. Such a flare location on the Sun offers a u nique possibility to investigate loop-top hard X-ray emission sources separ ately, without the presence of strong footpoint sources which can disturb t he observational characteristics of the loop-top sources during any process of image reconstruction. Hard X-ray radiation in all investigated hares ha s similar features: (1) smooth light curves with several impulsive spikes, (2) low-energy spectra (mainly below 33 keV) which can expressed in terms o f temperatures within the interval of about 20-100 MK. The HXR images show two types of loop-top emission sources: type A, co-spatial with the bright loop-top kernels seen in soft X-rays, and type B, having no distinct counte rpart in soft X-rays. Arguments are presented that this classification is m ore physical than the classification considering impulsive and gradual sour ces proposed by Masuda (1994), who actually separated two phases of evoluti on of the same loop-top source. The model of the turbulent flare kernel (Ja kimiec 1998; Jakimiec et al. 1998) has been adapted to explain the obtained characteristics of loop-top HXR emission sources of type A.