Fine Structure and Dynamics of the Inner Corona

Extract

High spectral (0,05 Å) and spatial (⋍ 1000 km) resolution spectra of the Fe XII line 1349.4 Å reveal the existence of coronal fine structures in the quiet sun against the solar disk. These coronal bright elements have an average size of 2000-3000 km; their column density can be 3 x 10¹⁷ cm ^–2 . In the quiet sun, outward streaming velocities of 10-15 km sec ^–1 can be measured by means of the Doppler effect. The total kinetic and thermal energy of the outstreaming gas can be estimated to be larger than 1 x 10 ⁵ ergs cm ^–2 sec ^–1, enough to account for the heating of the corona and the losses of the solar wind. At the outer limb (cos θ ⋍0.1) line profiles show a strong blue asymmetry, which could be caused by expanding material in a piston-driven shock, whereby the opaque, cool piston causes the asymmetry of the line profile.