arXiv subjects

T. J. Duckenfield

Publications and source records attributed to T. J. Duckenfield.

4 recordsLinked to original sources

arXiv2026

Analysing the highly irregular boundaries of solar pores

Solar pores possess irregular and evolving boundaries that are often far from the ideal circular flux tubes assumed in many magnetohydrodynamic (MHD) oscillation models. To tackle this irregularity in a consistent way for wave analysis, we introduce a framework that employs the convex hull of the pore boundary - derived from intensity minimum error thresholding - as the domain to perform further analysis. Using the modal assurance criterion, we find the range of pore shapes for which this approximation is valid. We demonstrate the usefulness of this framework by applying it to multi-height, high-cadence observations (4170 angstrom continuum, G-band, Na~\textsc{i}, and Ca~\textsc{ii}~K) of a solar pore, and apply Proper Orthogonal Decomposition of the convex hull to determine wave modes. The fundamental sausage ($m=1$) and kink ($m=2$) mode is found to remain reliable, while higher-order fluting modes ($m\ge3$) are strongly degraded by small-scale boundary irregularity. As expected, sausage-like modes dominate the variance at all heights and exhibit a systematic upward shift in frequency, consistent with freely propagating compressive waves. In contrast, the kink-like motions appear weak, confined to a persistent low-frequency peak, and most plausibly interpreted as a forced response to granular buffeting rather than a propagating mode. Together, these results establish a practical methodology for boundary-mode analysis in real, highly structured pores and provide new constraints on the nature and height evolution of MHD waves in the lower solar atmosphere.

astro-ph.SR↗

arXiv2025

Determining the Polarisation of a Coronal Standing Kink Oscillation Using Spectral Imaging Techniques with the Coronal Multi-channel Polarimeter (CoMP)

Coronal oscillations offer insight into energy transport and driving in the solar atmosphere. Knowing its polarisation state helps constrain a wave's displacement and velocity amplitude, improving estimates of wave energy flux and deposition rate. We demonstrate a method to combine imaging and spectral data to infer the polarisation of a coronal loop's standing kink wave, without the need for multiple instruments or multiple lines of sight. We use the unique capabilities of the Coronal Multi-channel Polarimeter (CoMP) to observe the standing kink mode of an off-limb coronal loop perturbed by an eruption. The full off-disk corona is observed using the 1074 nm Fe XIII spectral line, providing Doppler velocity, intensity and line width. By tracking the oscillatory motion of a loop apex in a time-distance map, we extract the line-of-sight (Doppler) velocity of the inhomogeneity as it sways and compare it with the derivative of its plane-of-sky displacement. This analysis provides the loop's velocity in two perpendicular planes as it oscillates with a period of $8.9^{+0.5}_{-0.5}$ minutes. Through detailed analysis of the phase relation between the transverse velocities we infer the kink oscillation to be horizontally polarised, oscillating in a plane tilted $-13.6^{+2.9}_{-3.0}$ degrees away from the plane of sky. The line widths show a periodic enhancement during the kink oscillation, exhibiting both the kink period and its double. This study is the first to combine direct imaging and spectral data to infer the polarisation of a coronal loop oscillation from a single viewpoint.

astro-ph.SR↗

arXiv2020

The effect of magnetic field on the damping of slow waves in the solar corona

Slow magnetoacoustic waves are routinely observed in astrophysical plasma systems such as the solar corona. As a slow wave propagates through a plasma, it modifies the equilibrium quantities of density, temperature, and magnetic field. In the corona and other plasma systems, the thermal equilibrium is comprised of a balance between continuous heating and cooling processes, the magnitudes of which vary with density, temperature and magnetic field. Thus the wave may induce a misbalance between these competing processes. Its back reaction on the wave has been shown to lead to dispersion, and amplification or damping, of the wave. In this work the importance of the effect of magnetic field in the rapid damping of slow waves in the solar corona by heating/cooling misbalance is evaluated and compared to the effects of thermal conduction. The two timescales characterising the effect of misbalance are derived and calculated for plasma systems with a range of typical coronal conditions. The predicted damping times of slow waves from thermal misbalance in the solar corona are found to be of the order of 10-100 minutes, coinciding with the wave periods and damping times observed. Moreover the slow wave damping by thermal misbalance is found to be comparable to the damping by field-aligned thermal conduction. We show that in the infinite field limit, the wave dynamics is insensitive to the dependence of the heating function on the magnetic field, and this approximation is found to be valid in the corona so long as the magnetic field strength is greater than 10G for quiescent loops and plumes and 100G for hot and dense loops. In summary thermal misbalance may damp slow magnetoacoustic waves rapidly in much of the corona, and its inclusion in our understanding of slow mode damping may resolve discrepancies between observations and theory relying on compressive viscosity and thermal conduction alone.

astro-ph.SR↗

arXiv2020

Seismological constraints on the solar coronal heating function

The hot solar corona exists because of the balance between radiative and conductive cooling and some counteracting heating mechanism which remains one of the major puzzles in solar physics. The coronal thermal equilibrium is perturbed by magnetoacoustic waves which are abundantly present in the corona, causing a misbalance between the heating and cooling rates. Due to this misbalance, the wave experiences a back-reaction, either losing or gaining energy from the energy supply that heats the plasma, at the time scales comparable to the wave period. In particular, the plasma can be subject to wave-induced instability or over-stability, depending on the specific choice of the coronal heating function. In the unstable case, the coronal thermal equilibrium would be violently destroyed, which does not allow for the existence of long-lived plasma structures typical for the corona. Based on this, we constrained the coronal heating function using observations of slow magnetoacoustic waves in various coronal plasma structures.

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