Heights of solar tracers observed at 8 mm and an interpretation of their radiation

Context. At the wavelength of 8 mm emissive features (high brightness temperatrue regions, HTRs) and absorptive features (low brightness temperature regions, LTRs) can be traced for the determination of the solar rotation. From earlier studies it is known that about two thirds of LTRs are associated with H" filmaments. Thermal bremsstrahlung and gyroresonant (cyclotron) radiation mechanism can be important to explain the observed phenomena. Aims. The goal of the present analysis is to determine the heights of solar structures observed at 8 mm and to interpret their radiation mechanism(s). Methods. We use the method for the simultaneous determination of the solar synodic rotation velocity and the height of tracers. The rotation velocities were determined by the linear least-square fit of their central meridian distance as a function of time. A procedure for calculating the brightness temperature for given wavelength and model atmosphere, integrating the radiative transfer equation for the thermal bremsstrahlung, is used. Results. The mean value of the low brightness temperature regions’ heights is about 45 600 km. This height was used as an input for constructing the prominence and coronal condensation models, which, assuming the thermal bremsstrahlung as the radiation mechanism, yield the decrease of the brightness temperature in the order of 2 ‐ 14 %, in agreement with observations. If the same radiation mechanism is considered, the models of the solar corona above ordinary active regions give an increase of the brightness temperature in the order of 5 ‐ 19 %, also in agreement with observations. In this latter case an indirect indication (from the rotational analysis) that the HTRs are located higher in the solar atmosphere than the LTRs was taken into account. Conclusions. The method for the simultaneous determination of the solar synodic rotation velocity and the height of tracers could have been properly applied only on LTRs, since a homogeneous distribution over latitudes and central meridian distances of a large enough data set is necessary. The thermal bremsstrahlung can explain both the LTR (prominences and coronal condensations) and HTR (ordinary active regions) phenomena.