scholarly journals Forward Modeling of Simulated Transverse Oscillations in Coronal Loops and the Influence of Background Emission

2021 ◽  
Vol 922 (1) ◽  
pp. 60
Author(s):  
Mijie Shi ◽  
Tom Van Doorsselaere ◽  
Patrick Antolin ◽  
Bo Li
Keyword(s):  
Energy Content ◽  
Spectral Lines ◽  
Forward Model ◽  
Doppler Velocity ◽  
Coronal Loops ◽  
Doppler Width ◽  
Transverse Waves ◽  
The Real ◽  
Background Emission ◽  
Transverse Oscillations

Abstract We simulate transverse oscillations in radiatively cooling coronal loops and forward-model their spectroscopic and imaging signatures, paying attention to the influence of background emission. The transverse oscillations are driven at one footpoint by a periodic velocity driver. A standing kink wave is subsequently formed and the loop cross section is deformed due to the Kelvin–Helmholtz instability, resulting in energy dissipation and heating at small scales. Besides the transverse motions, a long-period longitudinal flow is also generated due to the ponderomotive force induced slow wave. We then transform the simulated straight loop to a semi-torus loop and forward-model their spectrometer and imaging emissions, mimicking observations of Hinode/EIS and SDO/AIA. We find that the oscillation amplitudes of the intensity are different at different slit positions, but are roughly the same in different spectral lines or channels. X-t diagrams of both the Doppler velocity and the Doppler width show periodic signals. We also find that the background emission dramatically decreases the Doppler velocity, making the estimated kinetic energy two orders of magnitude smaller than the real value. Our results show that background subtraction can help recover the real oscillation velocity. These results are helpful for further understanding transverse oscillations in coronal loops and their observational signatures. However, they cast doubt on the spectroscopically estimated energy content of transverse waves using the Doppler velocity.

scholarly journals Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations

Solar Physics ◽  
2021 ◽  
Vol 296 (6) ◽  
Author(s):  
Thomas Williams ◽  
Robert W. Walsh ◽  
Stephane Regnier ◽  
Craig D. Johnston
Keyword(s):  
Energy Content ◽  
Time Lag ◽  
Low Frequency ◽  
Building Blocks ◽  
Coronal Loops ◽  
Loop Model ◽  
Solar Dynamics Observatory ◽  
Heat Deposition ◽  
Total Energy Content ◽  
Solar Dynamics

AbstractCoronal loops form the basic building blocks of the magnetically closed solar corona yet much is still to be determined concerning their possible fine-scale structuring and the rate of heat deposition within them. Using an improved multi-stranded loop model to better approximate the numerically challenging transition region, this article examines synthetic NASA Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) emission simulated in response to a series of prescribed spatially and temporally random, impulsive and localised heating events across numerous sub-loop elements with a strong weighting towards the base of the structure: the nanoflare heating scenario. The total number of strands and nanoflare repetition times is varied systematically in such a way that the total energy content remains approximately constant across all the cases analysed. Repeated time-lag detection during an emission time series provides a good approximation for the nanoflare repetition time for low-frequency heating. Furthermore, using a combination of AIA 171/193 and 193/211 channel ratios in combination with spectroscopic determination of the standard deviation of the loop-apex temperature over several hours alongside simulations from the outlined multi-stranded loop model, it is demonstrated that both the imposed heating rate and number of strands can be realised.

scholarly journals Undamped transverse oscillations of coronal loops as a self-oscillatory process

2016 ◽  
Vol 591 ◽  
pp. L5 ◽  
Author(s):  
V. M. Nakariakov ◽  
S. A. Anfinogentov ◽  
G. Nisticò ◽  
D.-H. Lee
Keyword(s):  
Oscillatory Process ◽  
Coronal Loops ◽  
Transverse Oscillations

scholarly journals Excitation of decay-less transverse oscillations of coronal loops by random motions

2020 ◽  
Vol 633 ◽  
pp. L8 ◽  
Author(s):  
A. N. Afanasyev ◽  
T. Van Doorsselaere ◽  
V. M. Nakariakov
Keyword(s):  
Broad Band ◽  
Random Excitation ◽  
Forced Oscillations ◽  
Oscillatory Process ◽  
Coronal Loops ◽  
Alternative Mechanism ◽  
Steady Flows ◽  
Kink Waves ◽  
Random Motions ◽  
Transverse Oscillations

Context. The relatively large-amplitude decaying regime of transverse oscillations of coronal loops has been known for two decades and has been interpreted in terms of magnetohydrodynamic kink modes of cylindrical plasma waveguides. In this regime oscillations decay in several cycles. Recent observational analysis has revealed so-called decay-less, small-amplitude oscillations, in which a multi-harmonic structure has been detected. Several models have been proposed to explain these oscillations. In particular, decay-less oscillations have been described in terms of standing kink waves driven with continuous mono-periodic motions of loop footpoints, in terms of a simple oscillator model of forced oscillations due to harmonic external force, and as a self-oscillatory process due to the interaction of a loop with quasi-steady flows. However, an alternative mechanism is needed to explain the simultaneous excitation of several longitudinal harmonics of the oscillation. Aims. We study the mechanism of random excitation of decay-less transverse oscillations of coronal loops. Methods. With a spatially one-dimensional and time-dependent analytical model taking into account effects of the wave damping and kink speed variation along the loop, we considered transverse loop oscillations driven by random motions of footpoints. The footpoint motions were modelled by broad-band coloured noise. Results. We found the excitation of loop eigenmodes and analysed their frequency ratios as well as the spatial structure of the oscillations along the loop. The obtained results successfully reproduce the observed properties of decay-less oscillations. In particular, excitation of eigenmodes of a loop as a resonator can explain the observed quasi-monochromatic nature of decay-less oscillations and the generation of multiple harmonics detected recently. Conclusions. We propose a mechanism that can interpret decay-less transverse oscillations of coronal loops in terms of kink waves randomly driven at the loop footpoints.

Spectral lines: Energy crisis: Seeking the real alternatives, II

IEEE Spectrum ◽  
1974 ◽  
Vol 11 (2) ◽  
pp. 33-33
Author(s):  
Donald Christiansen
Keyword(s):  
Spectral Lines ◽  
Energy Crisis ◽  
The Real

scholarly journals Isotope shift in the resonance line of magnesium

1936 ◽  
Vol 154 (883) ◽  
pp. 679-683 ◽  
Keyword(s):  
Emission Line ◽  
Hyperfine Structure ◽  
Atomic Beam ◽  
Resonance Line ◽  
Isotope Shift ◽  
Wave Length ◽  
Spectral Lines ◽  
The Other ◽  
Absorption Lines ◽  
Doppler Width

By making use of an atomic beam instead of an ordinary gas or vapour, it is possible to observe structures of spectral lines very much smaller than the normal Doppler width. The structure of resonance lines can thus be observed as fine absorption lines on the background of the emission line possessing the full Doppler width. This method was used by the present authors for the detection and measurement of the hyperfine structure of the resonance lines of potassium and sodium. The following paper gives an account of the investigation of the structure of the singlet resonance line (2852 A) of magnesium by the same method. The line was found to possess two components at a separation of 0.033 cm -1 , the component of longer wave-length being very much stronger than the other.

scholarly journals Signatures of red-shifted footpoints in the quiescent coronal loop system

2019 ◽  
Author(s):  
Yamini K. Rao ◽  
Abhishek K. Srivastava ◽  
Pradeep Kayshap ◽  
Bhola N. Dwivedi
Keyword(s):  
Spectral Data ◽  
Coronal Loop ◽  
Doppler Velocity ◽  
Coronal Loops ◽  
Solar Dynamics Observatory ◽  
Heating Mechanism ◽  
Multi Wavelength ◽  
Solar Dynamics ◽  
Impulsive Heating ◽  
Imaging Spectrograph

Abstract. We observed quiescent coronal loops using multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) on 2016 April 13. The flows at the footpoints of such loop systems are studied using spectral data from Interface Region Imaging Spectrograph (IRIS). The Doppler velocity distributions at the footpoints lying in the moss region show the negligible or small flows at Ni I, Mg II k3 and C II line corresponding to upper photospheric and chromospheric emissions. Significant red-shifts (downflows) ranging from (1 to 7) km s−1 are observed at Si IV (1393.78 Å; log(T/K) = 4.8) which is found to be consistent with the existing results regarding dynamical loop systems and moss regions. Such downflows agree well with the impulsive heating mechanism reported earlier.

ERROR ESTIMATION FOR PRESSURE BROADENING COEFFICIENT FROM FITTING OVERLAPPED SPECTRAL LINE WITH VOIGT PROFILE

2005 ◽  
Vol 19 (05) ◽  
pp. 239-247
Author(s):  
JIE-LI LIN ◽  
HONG LU
Keyword(s):  
Spectral Line ◽  
Error Estimation ◽  
Spectral Lines ◽  
Pressure Broadening ◽  
The Real ◽  
Voigt Profile ◽  
Two Component ◽  
Relative Errors ◽  
Center Distance

A series of relative errors ε of the pressure broadening coefficient γfit with respect to the real one γ0 from fitting overlapped spectrum which are composed of two lines with the Voigt profile, are deduced and analyzed in detail for different pressure ranges. ε is found to be related with the value of γ0 and the spectral center distance δυ0 of the two component spectral lines which are not resolved. The influence of δυ0, pressures P and γ0 on ε is discussed. This work can be taken as a useful reference for the analysis of the observed spectrum which is overlapped by two lines to achieve more precise results of γfit.

scholarly journals Transverse oscillations in solar coronal loops induced by propagating Alfvénic pulses

2005 ◽  
Vol 431 (3) ◽  
pp. 1095-1104 ◽  
Author(s):  
L. Del Zanna ◽  
E. Schaekens ◽  
M. Velli
Keyword(s):  
Coronal Loops ◽  
Transverse Oscillations ◽  
Solar Coronal
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