arXiv subjects

Martin Archer

Publications and source records attributed to Martin Archer.

5 recordsLinked to original sources

arXiv2024

Transient Upstream Mesoscale Structures: Drivers of Solar-Quiet Space Weather

In recent years, it has become increasingly clear that space weather disturbances can be triggered by transient upstream mesoscale structures (TUMS), independently of the occurrence of large-scale solar wind (SW) structures, such as interplanetary coronal mass ejections and stream interaction regions. Different types of magnetospheric pulsations, transient perturbations of the geomagnetic field and auroral structures are often observed during times when SW monitors indicate quiet conditions, and have been found to be associated to TUMS. In this mini-review we describe the space weather phenomena that have been associated with four of the largest-scale and the most energetic TUMS, namely hot flow anomalies, foreshock bubbles, travelling foreshocks and foreshock compressional boundaries. The space weather phenomena associated with TUMS tend to be more localized and less intense compared to geomagnetic storms. However, the quiet time space weather may occur more often since, especially during solar minima, quiet SW periods prevail over the perturbed times.

astro-ph.SR↗

arXiv2021

Demonstrating change from a drop-in space soundscape exhibit by using graffiti walls both before and after

Impact evaluation in public engagement necessarily requires measuring change. However, this is extremely challenging for drop-in activities due to their very nature. We present a novel method of impact evaluation which integrates graffiti walls into the experience both before and after the main drop-in activity. The activity in question was a soundscape exhibit, where young families experienced the usually inaudible sounds of near-Earth space in an immersive and accessible way. We apply two analysis techniques to the captured before and after data - quantitative linguistics and thematic analysis. These analyses reveal significant changes in participants' responses after the activity compared to before, namely an increased diversity in language used to describe space and altered conceptions of what space is like. The results demonstrate that the soundscape was surprisingly effective at innately communicating key aspects of the underlying science simply through the act of listening. The impacts also highlight the power of sonification in stimulating public engagement, which, through reflection, can lead to altered associations, perceptions, and understanding. Therefore, we show that this novel approach to drop-in activity evaluation, using graffiti walls both before and after the activity and applying rigorous analysis to this data, has the power to capture change and, thus, have a short-term impact. We suggest that commonly used evaluation tools suitable for drop-in activities, such as graffiti walls, should be integrated both before and after the main activity in general, rather than only using them afterwards as is typically the case.

physics.ed-ph↗

arXiv2020

Going beyond the one-off: How can STEM engagement programmes with young people have real lasting impact?

A major focus in the STEM public engagement sector concerns engaging with young people, typically through schools. The aims of these interventions are often to positively affect students' aspirations towards continuing STEM education and ultimately into STEM-related careers. Most schools engagement activities take the form of short one-off interventions that, while able to achieve positive outcomes, are limited in the extent to which they can have lasting impacts on aspirations. In this paper we discuss various different emerging programmes of repeated interventions with young people, assessing what impacts can realistically be expected. Short series of interventions appear also to suffer some limitations in the types of impacts achievable. However, deeper programmes that interact with both young people and those that influence them over significant periods of time (months to years) seem to be more effective in influencing aspirations. We discuss how developing a Theory of Change and considering young people's wider learning ecologies are required in enabling lasting impacts in a range of areas. Finally, we raise several sector-wide challenges to implementing and evaluating these emerging approaches.

physics.ed-ph↗

arXiv2015

What frequencies of standing surface waves can the subsolar magnetopause support?

It is has been proposed that the subsolar magnetopause may support its own eigenmode, consisting of propagating surface waves which reflect at the northern/southern ionospheres forming a standing wave. While the eigenfrequencies of these so-called Kruskal-Schwartzschild (KS) modes have been estimated under typical conditions, the potential distribution of frequencies over the full range of solar wind conditions is not know. Using models of the magnetosphere and magnetosheath applied to an entire solar cycle's worth of solar wind data, we perform time-of-flight calculations yielding a database of KS mode frequencies. Under non-storm times or northward interplanetary magnetic field (IMF), the most likely fundamental frequency is calculated to be $0.64_{-0.12}^{+0.03}$mHz, consistent with previous estimates and indirect observational evidence for such standing surface waves of the subsolar magnetopause. However, the distributions exhibit significant spread (of order $\pm$0.3mHz) demonstrating that KS mode frequencies, especially higher harmonics, should vary considerably depending on the solar wind conditions. The implications of such large spread on observational statistics are discussed. The subsolar magnetopause eigenfrequencies are found to be most dependent on the solar wind speed, southward component of the IMF and the Dst index, with the latter two being due to the erosion of the magnetosphere by reconnection and the former an effect of the expression for the surface wave phase speed. Finally, the possible occurrence of MPSEs is shown to be controlled by the dipole tilt angle.

physics.space-ph↗

arXiv2014

Global impacts of a Foreshock Bubble: Magnetosheath, magnetopause and ground-based observations

Using multipoint observations we show, for the first time, that Foreshock Bubbles (FBs) have a global impact on Earth's magnetosphere. We show that an FB, a transient kinetic phenomenon due to the interaction of backstreaming suprathermal ions with a discontinuity, modifies the total pressure upstream of the bow shock showing a decrease within the FB's core and sheath regions. Magnetosheath plasma is accelerated towards the the intersection of the FB's current sheet with the bow shock resulting in fast, sunward, flows as well as outward motion of the magnetopause. Ground-based magnetometers also show signatures of this magnetopause motion simultaneously across at least 7 hours of magnetic local time, corresponding to a distance of 21.5 RE transverse to the Sun-Earth line along the magnetopause. These observed global impacts of the FB are in agreement with previous simulations and in stark contrast to the known localised, smaller scale effects of Hot Flow Anomalies (HFAs).

physics.space-ph↗