arXiv subjects

Eleanor Murray

Publications and source records attributed to Eleanor Murray.

4 recordsLinked to original sources

arXiv2026

Sub-surface structural changes associated with successive 11-yr solar activity cycles have been progressively more confined near the surface: new helioseismic results on Cycles 22 -- 25 from BiSON

We use Sun-as-a-star helioseismology data, collected by the Birmingham Solar-Oscillations Network (BiSON), to examine the relationship between the solar-cycle-induced frequency shifts of whole-Sun, low-angular degree solar p modes and well-known proxies of global solar activity. Changes in behaviour between the low-frequency modes and proxies, which in a previous study we found had occurred on the declining phase of Cycle 23, appear to have persisted into Cycle 25. More striking is a significant change in the relationship for higher-frequency modes, which the new Cycle 25 data now reveal. The observed mean frequency shifts in Cycle 25 are much stronger than one would expect for these modes based on the relationship between the frequencies and proxies seen in previous cycles, in particular Cycle 22. In sum, Cycle 25 is as strong as Cycles 22 and 23 when observed in this higher-frequency seismic band, in marked contrast to the relative sizes of the cycles seen in the global activity proxies, where Cycle 25 is noticeably weaker. When considered alongside a systematic reduction of the sensitivity of the mid-frequency modes to activity over the past three cycles, these results suggest that sub-surface structural changes associated with successive 11-year cycles are becoming ever more progressively confined just beneath the solar surface.

astro-ph.SR↗

arXiv2026

The seismic diversity of four successive solar cycle minima as observed by the Birmingham Solar-Oscillations Network (BiSON)

We have used data collected by the Birmingham Solar-Oscillations Network (BiSON) to perform a helioseismic diagnosis of changes to the Sun's internal structure between four successive solar cycle minima, beginning with the minimum at the end of cycle 21 and ending with the recent minimum at the beginning of cycle 25. The unique duration of the BiSON database makes such a study possible. We used the low-degree BiSON p-mode frequencies to constrain structural changes between minima in the layers above $\approx 0.9 R_{\odot}$. We accomplished this by examining variations in the HeII ionisation zone signature; and by inverting the frequency differences to infer changes in the sound speed. Additionally, we employed frequency differences between various solar models that had subtle modifications to their internal structures to facilitate analysis of the observations. We find evidence for small, but marginally significant, changes in structure between different minima. The HeII signature was larger, and the sound speed in the range $\approx 0.93$ to $0.97 R_{\odot}$ was slightly higher, during the cycle 23/24 minimum, than during the other minima. The cycle 23/24 minimum was the deepest, as measured by proxies of global solar activity. These findings are consistent with magnetic flux levels having been lower in this minimum than the others, resulting in a higher gas pressure, higher temperatures, and higher sound speed. Our results demonstrate the potential of using asteroseismic data to perform similar analyses on other solar-type stars.

astro-ph.SR↗

arXiv2026

Constraints on sunspot group lifetimes from far-side Sun-as-a-star helioseismology with BiSON

Frequencies of low-degree solar p modes are sensitive to activity over the entire Sun, including the unobservable far-side hemisphere. When frequency shifts extracted from week-long BiSON datasets are fitted to a linear combination of observed near-side activity and a far-side proxy made from the near-side measures shifted by half the solar rotation period, the solution favours a slightly higher weighting from the far-side contribution. Here, we demonstrate that this unphysical mismatch is due to the inherent inaccuracy of the far-side proxy, which fails to capture active regions that evolve fully on the solar far side, or that evolve (or have evolved) significantly as they rotate off (or onto) the visible disc. By simulating the evolution of sunspot group areas over time, which act as a suitable measure of solar activity, we show that the solution is sensitive to the lifetime of the activity. Assuming an underlying mapping from maximum group areas $A_{\rm max}$ (measured in millionths of the solar hemispheric area, MSH) to group lifetimes $\tau$ (measured in days) of the form $\tau = \alpha A_{\rm max}$, we find that $\alpha \simeq 0.025^{+0.055}_{-0.016}\,\rm d\,MSH^{-1}$ gives results consistent with the BiSON finding. This is to be compared with the value of $\alpha = 0.1\,\rm d\,MSH^{-1}$ implied by the well-known Gnevyshev-Waldmeier rule. While our best-fitting $\alpha$ maps to an average group lifetime of $\tau \simeq 5^{+10}_{-3}\,\rm d$, the best-fitting distribution includes a reasonable fraction of groups with lifetimes longer than the solar rotation period, which is essential to reproducing the mismatch.

astro-ph.SR↗

arXiv2021

Quantifying Uncertainty in Infectious Disease Mechanistic Models

This primer describes the statistical uncertainty in mechanistic models and provides R code to quantify it. We begin with an overview of mechanistic models for infectious disease, and then describe the sources of statistical uncertainty in the context of a case study on SARS-CoV-2. We describe the statistical uncertainty as belonging to three categories: data uncertainty, stochastic uncertainty, and structural uncertainty. We demonstrate how to account for each of these via statistical uncertainty measures and sensitivity analyses broadly, as well as in a specific case study on estimating the basic reproductive number, $R_0$, for SARS-CoV-2.

stat.ME↗