Detection of High-Frequency Oscillations and Damping from Multi-slit Spectroscopic Observations of the Corona

Abstract

During the total solar eclipse of 11 July 2010, multi-slit spectroscopic observations of the solar corona were performed from Easter Island, Chile. To search for "high-frequency waves", observations were taken at a high cadence in the green line at 5303Å due to [Fe xiv] and the red line at 6374Å due to [Fe x].The data are analyzed to study the periodic variations in the intensity, Doppler velocity and line width using wavelet analysis. The data with high spectral and temporal resolution enabled us to study the rapid dynamical changes within coronal structures. We find that at certain locations each parameter shows significant oscillation with periods ranging from 6 -25 s. For the first time, we could detect damping of "high-frequency oscillations" with periods of the order of 10 s. If the observed damped oscillations are due to magnetohydrodynamic (MHD) waves then they can contribute significantly in the heating of the corona. From a statistical study we try to characterize the nature of the observed oscillations while looking at the distribution of power in different line parameters.

Impulsively Generated Sausage Waves in Coronal Tubes With Transversally Continuous Structuring

“…The quasi-periods P of a considerable fraction of these signals were of the order of seconds. While these measurements were largely spatially unresolved, more recent high-cadence instruments imaging the corona at total eclipses also indicated the presence in coronal loops of quasi-periodic signals both with P ∼ 4 − 7 seconds (Williams et al 2001(Williams et al , 2002Katsiyannis et al 2003) and with P ∼ 6 − 25 seconds (Samanta et al 2016). In addition, quasi-periodic pulsations (QPPs) in the lightcurves of solar flares with similar periods have also been measured using imaging instruments such as the Nobeyama Radioheliograph (NoRH, e.g., Asai et al 2001;Nakariakov et al 2003;Melnikov et al 2005;Kupriyanova et al 2013), SDO/AIA (e.g., Su et al 2012), and more recently with the Interface Region Imaging Spectrograph (IRIS, Tian et al 2016; see also De Pontieu et al 2014 for the description of IRIS).…”

Impulsively Generated Wave Trains in Coronal Structures. I. Effects of Transverse Structuring on Sausage Waves in Pressureless Tubes

“…In particular, the numerical studies by Nakariakov et al (2004) and Shestov et al (2015) showed that the period and amplitude modulations in the wave trains transform into Morlet spectra characterized by a narrow tail followed by a broad head. Given their shape, these spectra are called "crazy tadpoles", and were indeed found in both radio (e.g., Jelinek & Karlicky 2010;Karlický et al 2013) and optical measurements (e.g., Katsiyannis et al 2003;Samanta et al 2016). If the measured short-period signals can be interpreted this way, then their temporal and wavelet features can be exploited to yield such key information as the internal Alfvén speed, density contrast between loops and their surroundings, as well as the location of the impulsive source (e.g., Roberts et al 1984;Roberts 2008).…”

“…On the observational side, quasi-periodic signals with short periods in coronal emissions presumably from densityenhanced loops have been known since the 1960s (e.g., Parks & Winckler 1969, Frost 1969, Rosenberg 1970, McLean & Sheridan 1973; see Table 1 of Aschwanden et al 1999 for a comprehensive compilation of measurements prior to 2000). A substantial fraction of these measurements were made in optical passbands at total eclipses, and the measured quasiperiods range from 0.5 − 4 seconds (e.g., Pasachoff & Landman 1984;Pasachoff & Ladd 1987) to 4 − 7 seconds (Williams et al 2001(Williams et al , 2002Katsiyannis et al 2003) to 6 − 25 seconds (Samanta et al 2016). In other passbands, quasi-periodic pulsations (QPPs) with similar periods have been found in the lightcurves of solar flares as measured with such instruments as the Nobeyama Radioheliograph (NoRH, e.g., Asai et al 2001;Nakariakov et al 2003;Melnikov et al 2005;Kupriyanova et al 2013), SDO/AIA (e.g., Su et al 2012), and more recently with the Interface Region Imaging Spectrograph (IRIS, Tian et al 2016).…”

Observations of the solar corona during the total solar eclipse on 21 August 2017

“…However, our understanding of wave heating would not be complete and accurate without observations of high‐frequency waves. During total solar eclipses, a high cadence of observations can be easily achieved, which is beneficial to the study of high‐frequency waves in the corona (Samanta et al, 2016). During the 2017 solar eclipse, PKU's CRIT has acquired high‐quality images of the coronal red line with a cadence better than 0.5 second in a large field of view.…”