High-frequency Decayless Waves with Significant Energy in Solar Orbiter/EUI Observations

Abstract

High-frequency wave phenomena present a great deal of interest as one of the possible candidates to contribute to the energy input required to heat the corona as a part of the alternating current heating theory. However, the resolution of imaging instruments up until the Solar Orbiter has made it impossible to resolve the necessary time and spatial scales. The present paper reports on high-frequency transverse motions in a small loop located in a quiet-Sun region of the corona. The oscillations were observed with the High Resolution Imager in the Extreme Ultraviolet telescope (17.4 nm) of the Extreme Ultraviolet Imager instrument on board the Solar Orbiter. We detect two transverse oscillations in short loops with lengths of 4.5 and 11 Mm. The shorter loop displays an oscillation with a 14 s period and the longer a 30 s period. Despite the high resolution, no definitive identification as propagating or standing waves is possible. The velocity amplitudes are found to be equal to 72 and 125 km s−1, respectively, for the shorter and longer loops. Based on that, we also estimated the values of the energy flux contained in the loops—the energy flux of the 14 s oscillation is 1.9 kW m−2 and that of the 30 s oscillation is 6.5 kW m−2. While these oscillations have been observed in the quiet Sun, their energy fluxes are of the same order as the energy input required to heat the active solar corona. Numerical simulations were performed in order to reproduce the observed oscillations. The correspondence of the numerical results to the observations provides support to the estimates of energy content for the observations. Such high energy densities have not yet been observed in decayless coronal waves, and this is promising for coronal heating models based on wave damping.

Modeling of Transverse Oscillations Driven by p-modes in Short Coronal Loops

“…The oscillation period is 1-8 minutes while the loop length ranges from 14 to 42 Mm. Unlike previous observations (Anfinogentov et al 2015;Li & Long 2023;Petrova et al 2023), no obvious linear correlation was found between the oscillation period and loop length. Meanwhile, the distribution of the period shows a peak at about 5 minutes (see Figure 3 in Gao et al 2022a).…”

“…Recently, decayless oscillations have also been found in short coronal loops (50 Mm) with the high-resolution 174 A  images taken by the Extreme Ultraviolet Imager (EUI; Rochus et al 2020) on board the Solar Orbiter (SolO; Müller et al 2020). Petrova et al (2023) reported high-frequency oscillations in two coronal loops with lengths of 4.5 Mm and 11 Mm located in a quiet-Sun region. The measured periods are 14 and 30 s, much shorter than in longer coronal loops.…”

The Role of High-frequency Transverse Oscillations in Coronal Heating

“…The literature with details is summarized in Table 1. We need to note that among the oscillations we consider, while there are cases where the decayless oscillations were clearly identified as standing modes, there are cases where the interpretation of whether observed oscillations are standing or propagating waves still remains open (Gao et al 2022;Petrova et al 2023;Shrivastav et al 2023). In this study, all decayless oscillations we consider in this study are assumed to be standing modes.…”

“…The discovery of rapid decayless oscillations in smaller loop structures, which had not been observed due to the limitations of AIA's time cadence and spatial resolution, has been accelerated by the unprecedented high spatial and temporal resolution of the High Resolution Imager (HRI) of the Extreme Ultraviolet Imager (EUI; Rochus et al 2020) aboard the Solar Orbiter (SolO; Müller et al 2020). Petrova et al (2023) first discovered high-frequency transverse oscillations with periods of 30 and 14 s. Zhong et al (2022b) presented short-period (1-3 minutes) decayless oscillations simultaneously observed in both SolO/EUI and SDO/AIA for the first time. As the oscillation results in EUI and AIA are consistent with each other, it confirmed that the observations of high-frequency oscillations by EUI are robust.…”

“…Note that althoughDuckenfield et al (2018) found the second harmonic of decayless oscillation in the solar corona, only the first harmonic of decayless oscillation was considered here Zhong et al (2022b). reported oscillations detected with SDO/AIA and SolO/EUI simultaneously, but we only used oscillation results observed by EUI Petrova et al (2023). presented two possible loop lengths for each oscillation; thus we considered the average value of loop lengths Li & Long (2023).…”