On the nature of the chromospheric fine structure

Abstract

Abstract. We analyze a time series of forty high spatial and temporal resolution two-dimensional intensity and Doppler velocity images at different wavelengths within the Hα line. The observations were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph at THEMIS. We study the morphology of dark mottles and grains as seen in different wavelengths and examine their relation to the MDI magnetic field topology. We determine some physical properties of dark mottles with an inversion technique based on an iterative cloud model method with constant source function, giving the optical thickness τ 0 , the Doppler width ∆λ D , the velocity v and the source function S distribution along a structure. The obtained global properties of mottles as well as the spatial and temporal evolution of several physical parameters along the axes of individual mottles are discussed. The derived velocities in mottles as a function of space and time (time slice images) exhibit a quasi-periodic, bidirectional pattern. It is suggested that magnetic reconnection is the mechanism responsible for their formation and dynamics. Furthermore, a similar quasi-periodic behaviour of the Doppler velocity variations in dark grains and their morphological characteristics both suggest the similarity of dark mottles and grains.

Numerical simulations of spicule formation in the solar atmosphere

“…There are clear bi-directional flows in the spicule: downward at the centre and upward at the boundaries. This is fully consistent with the observational findings (Tsiropoula et al 1994;Tziotziou et al 2003Tziotziou et al , 2004Pasachoff et al 2009). After this moment, the central part of the spicule continues to subside, while the two small peaks from the previous snapshot become taller and exhibit a clear double structure in the region of 3.5 Mm < y < 4.5 Mm.…”

“…The 1D models may also produce the same properties. However, the advantage of the 2D model is that it may produce other observed properties of spicules, such as a double (sometimes multi) structure (Tanaka 1974;Dara et al 1998;Suematsu et al 2008) and bi-directional flows (Tsiropoula et al 1994;Tziotziou et al 2003Tziotziou et al , 2004Pasachoff et al 2009). This is clearly seen in Figs.…”

“…Despite significant achievements in the above-mentioned papers, there are still no existing mechanisms that explain the observed double structures of spicules (Tanaka 1974;Dara et al 1998;Suematsu et al 2008) and bi-directional flow (Tsiropoula et al 1994;Tziotziou et al 2003Tziotziou et al , 2004Pasachoff et al 2009). Suematsu et al (2008) and Tsiropoula et al (1994) have proposed a magnetic reconnection as an explanation of, respectively, the double structures and bi-directional flow.…”

Numerical simulations of solar macrospicules

“…A typical lifetime of spicules is 5−15 min with an average value of ∼7 min (Pasachoff et al 2009). Spicules consist of double-thread structures (Tanaka 1974;Dara et al 1998;Suematsu et al 2008) and they reveal the bi-directional flow (Tsiropoula et al 1994;Tziotziou et al 2003Tziotziou et al , 2004Pasachoff et al 2009). Typical electron temperature and electron density in spicules are respectively (15−17) × 10 3 K and 2×10 11 −3.5 × 10 10 cm −3 at altitudes of 4−10 Mm above the solar surface (Beckers 1968).…”

Fast imaging spectroscopy with MSDP spectrometers. Vector magnetic maps with THEMIS/MSDP

“…A third possibility is to use the mode 3 for H α alone, with the broad field stop 25 × 190 arcsec. As with VTT/MSDP, chromospheric structures were targets of published papers, as for example mottles and grains (Tziotziou et al 2003). But, of course, since THEMIS is a polarization-free telescope, the main applications of THEMIS/MSDP concern magnetic fields.…”