John C Coxon

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• PhD
• Ernest Rutherford Fellow at Northumbria University

High‐latitude ionospheric convection is a useful diagnostic of solar wind‐magnetosphere interactions and nightside activity in the magnetotail. For decades, the high‐latitude convection pattern has been mapped using the Super Dual Auroral Radar Network (SuperDARN), a distribution of ground‐based radars which are capable of measuring line‐of‐sight (...

Geomagnetically Induced Currents (GICs) are a severe space weather hazard, driven through coupling between the solar wind and magnetosphere. GICs are rarely measured directly, instead the ground magnetic field variability is often used as a proxy. Recently space weather models have been developed to forecast whether the magnetic field variability (...

Long-term reduction (∼20km) in the height of the ionospheric F2 layer, hmF2, is predicted to result from increased levels of tropospheric greenhouse gases. Sufficiently long sequences of ionospheric data exist in order for us to investigate this long-term change, recorded by a global network of ionosondes. However, direct measurements of ionospheri...

In this study, we investigate the effects caused by interplanetary (IP) shock impact angles on the subsequent ground dB/dt variations during substorms. IP shock impact angles have been revealed as a major factor controlling the subsequent geomagnetic activity, meaning that shocks with small inclinations with the Sun‐Earth line are more likely to tr...

We examine the statistical distribution of large‐scale Birkeland currents measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment in four unique categories of geomagnetic activity for the first time: quiet times, storm times, quiet‐time substorms, and storm‐time substorms. A novel method is employed to sort data into...

Long-term change in the height of the ionospheric F2 layer, hmF2, is predicted to result from increased levels of tropospheric greenhouse gases. Sufficiently long sequences of ionospheric data exist to investigate this long-term change, recorded by a global network of ionosondes. However, direct measurements of ionospheric layer height with these i...

This study presents a re‐evaluation of the Kullen and Janhunen (2004, https://doi.org/10.5194/angeo-22-951-2004) global northward interplanetary magnetic field (IMF) simulation, using the Grand Unified Magnetosphere–Ionosphere Coupling Simulation version 4 (GUMICS‐4), a global MHD model. We investigate the dynamic coupling between northward IMF con...

Bias exists in letters of recommendation, and it is reflected in the language used to describe and evaluate different candidates for countless opportunities in academia. Professional organizations are becoming more aware of this issue, and are pursuing avenues to address it. This paper discusses the type of information, that is, useful to have on h...

The response of the Earth’s magnetotail current sheet to the external solar wind driver is highly time-dependent and asymmetric. For example, the current sheet twists in response to variations in the By component of the interplanetary magnetic field (IMF), and is hinged by the dipole tilt. Understanding the timescales over which these asymmetries m...

Report on the RAS Specialist Discussion Meeting ‘System-scale observations and modelling of solar wind-magnetosphere-ionosphere-thermosphere (SW-M-I-T) coupling’.

We analyze probability distributions of Birkeland current densities measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment. We find that the distributions are leptokurtic rather than normal and they are sometimes heavy‐tailed. We fit q‐exponential functions to the distributions and use these to estimate where the lar...

Angeline G Burrell, McArthur Jones Jr, Alexa Halford, Kate Zawdie and John Coxon have collaborated to create a set of tools to tackle conscious and unconscious bias in space physics research

We examine the magnetotail using data from the Hot Ion Analyzer on Cluster 1 during 2001–2009. We develop and utilize an algorithm in order to identify times during which Cluster 1 is in the magnetotail lobe but observes plasma, which is hotter than our expectations of the lobe. We analyze the prevailing Interplanetary Magnetic Field (IMF) BZ condi...

We analyze the spatial variation in the response of the surface geomagnetic field (or the equivalent ionospheric current) to variations in the solar wind. Specifically, we regress a reanalysis of surface external and induced magnetic field (SEIMF) variations onto measurements of the solar wind. The regression is performed in monthly sets, independe...

The high latitude, lobe regions of the magnetosphere are often assumed to contain cool, low energy plasma populations. However, during periods of northward Interplanetary Magnetic Field, energetic plasma populations have occasionally been observed. We present three cases when Cluster observed uncharacteristically “hot” plasma populations in the lob...

This is the third in a series of papers that investigate the semi-annual, annual and Universal Time variations in the magnetosphere. In this paper we use the Lin et al. (2010) empirical model of magnetopause locations, along with the assumption of pressure equilibrium and the Newtonian approximation of magnetosheath pressure. We show that the equin...

This is the second in a series of papers that investigate the semi-annual, annual and Universal Time ( UT ) variations in the magnetosphere. We present a varied collection of empirical results that can be used to constrain theories and modelling of these variations. An initial study of two years’ data on transpolar voltage shows that there is a sem...

p>We present a multi-instrumental study of ionospheric irregularities of different scales (from tens of centimeters to few kilometers) observed over the Central and East Siberia, Russia, during a moderate-to-strong geomagnetic storm on 27–28 May 2017. From high-frequency (HF) and ultrahigh-frequency (UHF) radar data, we observed an intense auroral...

We study the semi-annual variation in geomagnetic activity, as detected in the geomagnetic indices am , aa H , AL , Dst and the four a s indices derived for 6-hour MLT sectors (around noon, dawn, dusk and midnight). For each we compare the amplitude of the semi-annual variation, as a fraction of the overall mean, to that of the corresponding variat...

The open magnetic flux content of the magnetosphere varies during substorms as a result of dayside and nightside reconnection. The open flux can be calculated from the area of the polar cap, delineated by the open‐closed field line boundary (OCB). This study presents a superposed epoch analysis of the location of the OCB and the change in the magne...

Plain Language Summary Planets with a magnetic field carve out a cavity, or “magnetosphere” in the solar wind. The magnetosphere of Mercury, like that of Earth, is driven by a process called“magnetic reconnection”, in which magnetic fields from the Sun and the planet interconnect. Reconnection at Mercury (and Earth) occurs in bursts called “flux tr...

In this paper, we present Magnetospheric Multiscale (MMS) observations of a flux transfer event (FTE) characterized by a clear signature in the magnetic field magnitude, which shows maximum at the center flanked by two depressions, detected during a period of stable southward interplanetary magnetic field. This class of FTEs are called “crater‐FTEs...

We obtain current densities from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), alongside By and Bz from the Interplanetary Magnetic Field (IMF) for March 2010. For each AMPERE spatial coordinate, we cross‐correlate current density with By and Bz, finding the maximum correlation for lags up to 360 min. The patt...

We analyze the spatial variation in the response of the surface geomagnetic field (or the equivalent ionospheric current) to variations in the solar wind. Specifically, we regress a reanalysis of surface external and induced magnetic field (SEIMF) variations onto measurements of the solar wind. The regression is performed in monthly sets, independe...

A simple Monte Carlo model is presented that considers the effects of spacecraft orbital sampling on the inferred distribution of magnetic flux ropes, generated through magnetic reconnection in the magnetotail current sheet. When generalized, the model allows the determination of the number of orbits required to constrain the underlying population...

A Monte Carlo method of investigating the effects of placing selection criteria on the magnetic signature of in situ encounters with flux ropes is presented. The technique is applied to two recent flux rope surveys of MESSENGER data within the Hermean magnetotail. It is found that the different criteria placed upon the signatures will preferentiall...

John Coxon, Jasmine Sandhu, Gabby Provan and Jim Wild summarize the content and conclusions of the “Collaborative Public Engagement with MIST Science” meeting held in September.

Principal component analysis is performed on Birkeland or field-aligned current (FAC) measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, to determine the response of dayside and nightside FACs to reversals in the orientation of the interplanetary magnetic field (IMF) and the occurrence of substorms. Daysid...

During geomagnetic substorms, around 1015 J of energy is extracted from the solar wind and processed by the Earth's magnetosphere. Prior to the onset of substorm expansion phases, this energy is thought to be largely stored as an increase in the magnetic field in the magnetotail lobes. However, how, when, and where this energy is stored and release...

Jasmine Sandhu, Georgina Graham, Sarah Bentley and John Coxon report on the annual Magnetosphere, Ionosphere, and Solar–Terrestrial (MIST) meeting, highlighting science results from the Cassini and Juno missions.

Field-aligned currents (FACs), also known as Birkeland currents, are the agents by which energy and momentum are transferred to the ionosphere from the magnetosphere and solar wind. This coupling is enhanced at substorm onset through the formation of the substorm current wedge. Using FAC data from the Active Magnetosphere and Planetary Electrodynam...

We review research into the Birkeland currents (also known as field‐aligned currents) that has been conducted using the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). We open with a short review of the history of research into the Birkeland current systems, before describing the conception of AMPERE and its roots i...

We use a global magnetohydrodynamics simulation to analyze transient magnetic reconnection processes at the magnetopause. The solar wind conditions have been kept constant and an interplanetary magnetic field (IMF) with large duskward BY and southward BZ components has been imposed. Five flux transfer events (FTEs) with clear bipolar magnetic field...

Flux transfer events are bursts of reconnection at the dayside magnetopause, which give rise to characteristic signatures observed by a range of magnetospheric/ionospheric instrumentation. One outstanding problem is that there is a fundamental mismatch between space-based and ionospheric estimates of the flux that is opened by each flux transfer ev...

Sarah Badman, John Coxon, Katie Raymer and Arianna Sorba report from the annual magnetosphere, ionosphere and solar–terrestrial (MIST) meeting, which focused on new approaches to data analysis in MIST science.

We conduct a superposed epoch analysis of Birkeland current densities from AMPERE (Active Magnetosphere and Planetary Electrodynamics Response Experiment) using isolated substorm expansion phase onsets identified by an independently derived data set. In order to evaluate whether R1 and R2 currents contribute to the substorm current wedge, we rotate...

The solar-wind magnetosphere interaction primarily occurs at altitudes where the dipole component of Earth’s magnetic field is dominating. The disturbances that are created in this interaction propagate along magnetic field lines and interact with the ionosphere–thermosphere system. At ionospheric altitudes, the Earth’s field deviates significantly...

We review the morphology and dynamics of the electrical current systems of the terrestrial magnetosphere and ionosphere. Observations from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) over the three years 2010 to 2012 are employed to illustrate the variability of the field-aligned currents that couple the magn...

We reduce measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to give the total Birkeland (field-aligned) current flowing in both hemispheres in monthly and hourly bins. We analyze these totals using 6 years of data (2010-2015) to examine solar zenith angle-driven variations in the total Birkelan...

The solar-wind magnetosphere interaction primarily occurs at altitudes where the dipole component of Earth's magnetic field is dominating. The disturbances that are created in this interaction propagate along magnetic field lines and interact with the ionosphere-thermosphere system. At ionospheric altitudes, the Earth's field deviates significantly...

We present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices. By being able to prescribe different percentile values, we can determine the onset and duration of substorm phases for smaller...

John Coxon and colleagues sum up a Magnetosphere, Ionosphere and Solar–Terrestrial meeting that touched on topics across the solar system.

Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently e...

We reduce measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to give the total Birkeland (field-aligned) current flowing in both hemispheres in monthly and hourly bins. We analyze these totals using 6 years of data (2010-2015) to examine solar zenith angle-driven variations in the total Birkelan...

We describe a novel method for identifying times when a spacecraft is in Earth's magnetotail lobes solely using magnetometer data. We propose that lobe intervals can be well identified as times when the magnetic field is strong and relatively invariant, defined using thresholds in the magnitude of BX and the standard deviation σ of the magnetic fie...

We present the first large scale comparison of the spatial distribution of field aligned currents as measured by the Active Magnetosphere and Planetary Electrodynamics Response Experiment, with the location and brightness of the average auroral oval, determined from the Imager for Magnetopause-to-Aurora Global Exploration far ultraviolet instrument...

We describe a novel method for identifying times when a spacecraft is in Earth’s magnetotail lobes solely using magnetometer data. We propose that lobe intervals can be well identified as times when the magnetic field is strong and relatively invariant, defined using thresholds in the magnitude of BX and the standard deviation ???? of the magnetic...

We present a new quantitative technique that determines the times and durations of substorm expansion and recovery phases and possible growth phases based on percentiles of the rate of change of auroral electrojet indices. By being able to prescribe different percentile values, we can determine the onset and duration of substorm phases for smaller...

During substorm growth phases, magnetic reconnection at the magnetopause extracts ~1015 J from the solar wind which is then stored in the magnetotail lobes. Plasma sheet pressure increases to balance magnetic flux density increases in the lobes. Here, we examine plasma sheet pressure, density and temperature during substorm growth phases using nine...

In this paper we present the first large-scale statistical study of the influence of magnetic reconnection on the magnitude of the region 1 and region 2 Birkeland field-aligned currents (FACs). Whilst previous studies have employed single spacecraft measurements to construct a statistical picture of the location and density of the Birkeland current...

Unprecedented spacecraft and instrumental coverage and the isolated nature and distinct step-like development of a substorm on 17 March 2010 has allowed validation of the two-loop substorm current wedge model (SCW2L). We find a close spatio-temporal relationship of the SCW with many other essential signatures of substorm activity in the magnetotail...

We perform a superposed epoch analysis of the evolution of the Birkeland currents (field-aligned currents) observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) during substorms. The study is comprised of 2900 substorms provided by the SuperMAG experiment. We find that the current ovals expand and contract...

[1] Using the location of maximum region 1 current determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment as a proxy for the open/closed field line boundary, we monitor the evolution of the amount of open magnetic flux inside the magnetosphere during 772 substorms. We then divide all substorms into three classes, d...

We use current density data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to identify the location of maximum region 1 current at all magnetic local times (MLTs). We term this location the R1 oval. Comparing the R1 oval location with particle precipitation boundaries identified in DMSP data, we find that t...