Chromospheric Peculiar Off-limb Dynamical Events from IRIS Observations

Abstract

To study motions and oscillations in the solar chromosphere and at the transition region (TR) level we analyze some extreme Doppler shifts observed off-limb with the Interface Region Imaging Spectrograph (IRIS). Raster scans and slit-jaw imaging observations performed in the near-ultraviolet (NUV) channels were used. Large transverse oscillations are revealed by the far wings profiles after accurately removing the bulk average line profiles of each sequence. Different regions around the Sun are considered. Accordingly, the cool material of spicules is observed in Mg II lines rather dispersed up to coronal heights. In the quiet Sun and especially in a polar coronal hole, we study dynamical properties of the dispersed spiculesmaterial off-limb using a high spectral, temporal and spatial resolutions IRIS observations. We suggest that numerous smallscale jet-like spicules show rapid twisting and swaying motions evidenced by the large distortion and dispersion of the line profiles, including impressive periodic Doppler shifts. Most of these events repeatedly appear in red-and blue-shifts above the limb throughout the whole interval of the observation datasets with an average swaying speed of order ±35 kms -1 reaching a maximum value of 50 km s -1 in the polar coronal hole region, well above the 2.2 Mm heights. We identified for the 1 st time waves with a short period of order of 100 sec and less and transverse amplitudes of order of ± 20 to 30 km s -1 with the definite signature of Alfven waves. No correlation exists between brightness and Doppler shift variations; the phase speed of the wave is very large and cannot definitely be determined from the spectral features seen along the quasi-radial features. Even shorter periods waves are evidenced, although their contrast is greatly attenuated by the overlapping effects along the line of sight.

A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS)

“…A characteristic signature of this process is a doubling of the wave frequency and therefore the generation of high-frequency waves (Shoda and Yokoyama, 2018), which are commonly detected in spicules (e.g. Okamoto and De Pontieu, 2011;Srivastava et al, 2017;Tavabi and Koutchmy, 2019).…”

“…Another manifestation of "snowflakes in the oven" on the Sun is prominences (Tandberg-Hanssen, 1995;Vial and Engvold, 2015), some mysteriously cool and dense material found at elevated heights in the hot and tenuous corona. Unlike coronal rain, which is usually small in size and transient in time, prominences are relatively large-scale, long-lived structures that generally appear as bright emission at the limb and dark absorption on the solar disk (thus called filaments).…”

Dynamics of Explosive Events Observed by the Interface Region Imaging Spectrograph

“…IRIS spacecraft contained a combination of telescope and spectrograph (De Pontieu et al, 2014b). IRIS obtains bservations of the solar transition region with a high spatial and spectral resolution to investigate the physical processes of fine structures (Chen et al, 2019, Tavabi and Koutchmy, 2019, Zeighami, Tavabi, and Amirkhanlou, 2020, Bose et al, 2021a. The spectral dispersion in the far and near-ltraviolet are about 0.025 Å and 0.053 Å, respectively.…”

“…Thereafter the term transition region explosive events (TREEs) is also used (Dere, Bartoe, and Brueckner, 1984). Some EEs could also produce enhancements in spectra of C I, C II, O I, and Mg II (Dere, Bartoe, and Brueckner, 1989;Dere, 1992;Zhang et al, 2010, andKoutchmy, 2019). EEs are repeatedly noted in observations (Chae et al, 1998, Ning, Innes, and Solanki, 2004, and Doyle, Popescu, and Taroyan, 2006.…”

“…In the image processing method, displacements and intensity changes in images are measured (Tavabi et al, 2015a). In the second method, periodic patterns in Doppler shifts are examined by spectrometers Golub, 2015, Tavabi, 2018;Koutchmy, 2019, andAmirkhanlou, 2020).…”