Non‐rigid rotation of solar spicules

Abstract

Ha profiles of chromospheric spicules computed for a variety of rotational behavior are compared with an observed profile, which was derived by averaging 11 H a profiles taken near times of maximum spicule intensity. If turbulent velocity is small or equals zero, calculated profiles are in good agreement with the observed one under the conditions that rotation is non-rigid (faster rotation further away from the axis of the spicule) and the source function decreases in the direction from the spicule axis to the periphery. The comparison of calculated and observed tilts of spicule spectra relative to the direction of dispersion seems to corraborate the non-rigid character of spicular rotation.Key words: Sun -chromosphere -spicules A A A subject classification: 073 IntroductionTilts of spicule spectra relative to the direction of dispersion as well as large widths of spicule emission lines point to the possible presence of rotation in spicules. Large observed widths of spicular profiles may be explained by several causes other than rotation: high temperatures, large optical depths of spicules and broadening of profiles because of the self-absorption, the high turbulence of the spicular plasma, the superposition of some spectral features with different Doppler shifts in the line of sight, or the radial compression or expansion of spicules while conserving axial symmetry. But any one of these factors alone can not completely satisfy all the observational d a t a (Livshitz 1966, Beckers 1968, Beckers 1972, Ivanchuk and Pishkalo 1989, Ivanchuk and Pishkalo 1992.Tilted spectral features have been explained most simply as due to the superposition of several neighbouring spicules with different Doppler shifts in the line of sight, because of still insufficient spatial resolution of the observations. However, tilts are also observed at large heights in the chromosphere, where the superposition is unlikely. Therefore, spectral tilts cannot be fully explained by superposition of several different spicules in the line of sight (Beckers 1966, Pasachoff et al. 1968.It seems rather probable that tilts are real phenomena because oftilts are observed at times of good seeing and because features with large Doppler shifts and spatially isolated narrow features also have tilts (Beckers 1966, Alissandrakis 1973, Krall et al. 1976, Pishkalo 1986).In Ha and K C a I1 lines, observed spectral tilts reach several degrees. Pishkalo (1986) estimated that 28%of Ha spicules had non-zero tilts and the averaged tilt of these spicules was 1'25'. Many spicules had spectral tilts in isolated moments of their lifetimes only. A tilt occured during brief time intervals for about 50% of all the spicules. There are also examples where t h e tilt was constant for a prolonged time interval (about 4 minutes) and where the tilt changed steadily and might even reverse its sign (Pasachoff et al. 1968, Pishkalo 1986.T h e calculations and the analysis of the rotation effects on broadening of spicule profiles made by Rodionov (1968), Avery (1970), Mamedov and...

Oscillations and Waves in Solar Spicules

“…It must be mentioned here, that some observations show the tilt of spicule spectra relative to the direction of dispersion, which was explained as due to the rotation of spicules around their axes (Pasachoff et al (1968); Rompolt (1975); Pishkalo (1994)).…”

“…These periodic perturbations are the subject of our discussion in the remaining part of the paper. It must be mentioned here, that some observations show the tilt of spicule spectra relative to the direction of dispersion, which was explained as due to the rotation of spicules around their axes (Pasachoff et al (1968); Rompolt (1975); Pishkalo (1994)). In this regards, it is interesting to note the recent SOHO/CDS observations, which also suggest the rotation in macro-spicules, interpreted as a sort of giant solar tornado (Pike and Mason (1998)).…”

The Nonlinear Evolution of a Twist in a Magnetic Shocktube

“…Examples include siphon flows in coronal loops (Orlando et al 1995a(Orlando et al , 1995b, counterstreaming (Lin et al 2003), and field-aligned flows within filament channels (Lin et al 2005), spicules (Hollweg et al 1982;De Pontieu et al 2004;Zaqarashvili & Erdélyi 2009;Scullion et al 2011), Evershed flows within sunspots (Montesinos & Thomas 1997;Plaza et al 1997). In addition, non-thermal broadenings have been observed within the chromosphere (Beckers 1968(Beckers , 1972Pishkalo 1994;Jess et al 2009Jess et al , 2015. These non-thermal broadenings are usually interpreted as Alfvén waves and have been considered as a possible mechanism responsible for Type-I spicule formation (Hollweg et al 1982;Sterling & Hollweg 1988;Hollweg 1992;Kudoh & Shibata 1999;James et al 2003; though it is possible that other mechanisms such as leakage of p-mode oscillations along inclined field lines are responsible (De Pontieu et al 2004).…”

Can ion-neutral damping help to form spicules?

“…Pishkalo (1994) found that about half of all spicules showed spectral tilts at some point in their lifetimes and that rotation must be in the range of 20−35 km s −1 to fit the observed spectral profiles.…”