Dynamics of Hα spicules according to spectral observations at various heights of the solar chromosphere

Abstract

Almost simultaneous height sequences of 69 spicules in the Hα line have been studied. The spectra are obtained at six heights during 6 s on the east side of the solar disk with the 53-cm Lyot coronagraph of Abastumani Astrophysical Observatory.

Radial velocities V _r, total intensities or equivalent widths W, full widths at half maximum of intensity (FWHM) at all heights are determined (about 300 profiles of the Hα line). It is found that:

• (1) Absolute values of radial velocities increase linearly with the height (see Equation (1));

• (2) variation of the sign of the radial velocity along single spicules was never observed.

These results combined with the findings on the spicules radial velocities and shifts obtained earlier (Kulidzanishvili and Nikolsky, 1978; Nikolsky and Platova, 1970) led us to the conclusion that the 5-min tangential oscillations of spicules involve the entire spicule at once.

The intensity height scales for single spicules and for the chromosphere ‘in toto’ are determined; they turned out to be 2.5 × 10³ km and 1.9 × 10³ km respectively (see Equations (2) and (3)).

The dependence curve of the Hα line half-widths Δλ on the height h is drawn. The Hα line half-width for those spicule groups which are traced at all heights (10 spicules) decreases with the height (Figure 4); for the majority (∼60 spicules) it remains essentially constant. Non-thermal ‘turbulent’ velocities V _t, in Hα spicules are defined. A mean value of the ‘turbulent’ velocity V _t at T = 6000° appeared to be 20–30km s⁻¹.

The hydrogen concentration in the spicules at 5000 km is 6 × 10¹¹ cm⁻³.