S. E. Milan - Department of Physics and Astronomy, University of Leicester, UK

S. E. Milan
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Name
S. E. Milan
Affiliation
Department of Physics and Astronomy, University of Leicester, UK
City
Leicester
Country
United Kingdom

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Physics - Space Physics (13)
 
Earth and Planetary Astrophysics (2)
 
Instrumentation and Methods for Astrophysics (1)

Publications Authored By S. E. Milan

During southward interplanetary magnetic field, dayside reconnection will drive the Dungey cycle in the magnetosphere, which is manifested as a two-cell convection pattern in the ionosphere. We address the response of the ionospheric convection to changes in the dayside reconnection rate by examining magnetic field perturbations at 780 km altitude. The Active Magnetosphere and Planetary Electrodynamics Response Experiment data products derived from the Iridium constellation provide global maps of the magnetic field perturbations. Read More

Electric currents flowing through near-Earth space ($\textit{R}$ $\leq$12 $\mathit{R}_{E}$) can support a highly distorted magnetic field topology, changing particle drift paths and therefore having a nonlinear feedback on the currents themselves. A number of current systems exist in the magnetosphere, most commonly defined as (1) the dayside magnetopause Chapman-Ferraro currents, (2) the Birkeland field-aligned currents with high latitude "region 1" and lower-latitude "region 2" currents connected to the partial ring current, (3) the magnetotail currents, and (4) the symmetric ring current. In the near-Earth nightside region, however, several of these current systems flow in close proximity to each other. Read More

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 Birkeland current flowing in both hemispheres, simultaneously, for the first time. A diurnal variation is identified in the total Birkeland current flowing, consistent with variations in the solar zenith angle. Read More

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 from a dipole. Read More

Here we present an event where simultaneous global imaging of the aurora from both hemispheres reveals a large longitudinal shift of the nightside aurora of about 3 h, being the largest relative shift reported on from conjugate auroral imaging. This is interpreted as evidence of closed field lines having very asymmetric footpoints associated with the persistent positive $\textit{y}$ component of the interplanetary magnetic field before and during the event. At the same time, the Super Dual Auroral Radar Network observes the ionospheric nightside convection throat region in both hemispheres. Read More

We present calculations of the auroral radio powers expected from exoplanets with magnetospheres driven by an Earth-like magnetospheric interaction with the solar wind. Specifically, we compute the twin cell-vortical ionospheric flows, currents, and resulting radio powers resulting from a Dungey cycle process driven by dayside and nightside magnetic reconnection, as a function of planetary orbital distance and magnetic field strength. We include saturation of the magnetospheric convection, as observed at the terrestrial magnetosphere, and we present power law approximations for the convection potentials, radio powers and spectral flux densities. Read More

Magnetic perturbations on ground at high latitudes are directly associated only with the divergence-free component of the height-integrated horizontal ionospheric current, $\textbf{J}_{\perp,df}$. Here we show how $\textbf{J}_{\perp,df}$ can be expressed as the total horizontal current $\textbf{J}_\perp$ minus its curl-free component, the latter being completely determined by the global Birkeland current pattern. Thus in regions where $\textbf{J}_\perp = 0$, the global Birkeland current distribution alone determines the local magnetic perturbation. Read More

In the exploration of global-scale features of the Earth's aurora, little attention has been given to the radial component of the Interplanetary Magnetic Field (IMF). This study investigates the global auroral response in both hemispheres when the IMF is southward and lies in the $\textit{xz}$ plane. We present a statistical study of the average auroral response in the 12-24 magnetic local time (MLT) sector to an $\textit{x}$ component in the IMF. Read More

We used the Lyon-Fedder-Mobarry global magnetohydrodynamics model to study the effects of the interplanetary magnetic field (IMF) IMF $\mathit{B}_{y}$ component on the coupling between the solar wind and magnetosphere-ionosphere system. When the IMF reconnects with the terrestrial magnetic field with IMF $\mathit{B}_{y}$ $\neq$ 0, flux transport is asymmetrically distributed between the two hemispheres. We describe how $\mathit{B}_{y}$ is induced in the closed magnetosphere on both the dayside and nightside and present the governing equations. Read More

Principal component analysis is performed on Birkeland or field-aligned current (FAC) measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment. Principal component analysis (PCA) identifies the patterns in the FACs that respond coherently to different aspects of geomagnetic activity. The regions 1 and 2 current system is shown to be the most reproducible feature of the currents, followed by cusp currents associated with magnetic tension forces on newly reconnected field lines. Read More

Ground magnetic field measurements can be mathematically related to an overhead ionospheric equivalent current. In this study we look in detail at how the global equivalent current, calculated using more than 30 years of SuperMAG magnetometer data, changes with sunlight conditions. The calculations are done using spherical harmonic analysis in quasi-dipole coordinates, a technique which leads to improved accuracy compared to previous studies. Read More

Flux transfer events (FTEs) are the manifestation of bursty and/or patchy magnetic reconnection at the magnetopause. We compare two sequences of the ionospheric signatures of flux transfer events observed in global auroral imagery and coherent ionospheric radar measurements. Both sequences were observed during very similar seasonal and interplanetary magnetic field (IMF) conditions, though with differing solar wind speed. Read More

Transpolar arcs and cusp spots are both auroral phenomena which occur when the interplanetary magnetic field is northward. Transpolar arcs are associated with magnetic reconnection in the magnetotail, which closes magnetic flux and results in a "wedge" of closed flux which remains trapped, embedded in the magnetotail lobe. The cusp spot is an indicator of lobe reconnection at the high-latitude magnetopause; in its simplest case, lobe reconnection redistributes open flux without resulting in any net change in the open flux content of the magnetosphere. Read More

The response of the Earth's magnetosphere to changing solar wind conditions are studied with a 3D Magnetohydrodynamic (MHD) model. One full year (155 Cluster orbits) of the Earth's magnetosphere is simulated using Grand Unified Magnetosphere Ionosphere Coupling simulation (GUMICS-4) magnetohydrodynamic code. Real solar wind measurements are given to the code as input to create the longest lasting global magnetohydrodynamics simulation to date. Read More

2011Jul
Affiliations: 1University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking, Surrey, UK, 2Department of Physics and Astronomy, University of Leicester, UK, 3Blackett Laboratory, Imperial College London, UK, 4NASA Goddard Space Flight Center, Greenbelt, MD, 5Department of Physics and Astronomy, University of Leicester, UK, 6Blackett Laboratory, Imperial College London, UK, 7Department of Physics and Astronomy, University of Leicester, UK, 8Blackett Laboratory, Imperial College London, UK, 9University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking, Surrey, UK, 10University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking, Surrey, UK, 11Astrium Ltd, Stevenage, UK, 12Department of Physics and Astronomy, University of Leicester, UK, 13University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking, Surrey, UK, 14Astrium Ltd, Stevenage, UK, 15Department of Physics and Astronomy, University of Leicester, UK, 16University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking, Surrey, UK, 17NASA Goddard Space Flight Center, Greenbelt, MD, 18Department of Physics and Astronomy, University of Leicester, UK, 19University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking, Surrey, UK, 20Department of Physics and Astronomy, University of Leicester, UK, 21University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking, Surrey, UK, 22LATMOS/Institute Pierre Simon Laplace, Paris, France, 23Department of Physics and Astronomy, University of Leicester, UK, 24NASA Goddard Space Flight Center, Greenbelt, MD, 25Department of Physics and Astronomy, University of Leicester, UK

Planetary plasma and magnetic field environments can be studied by in situ measurements or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques, which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth's magnetosphere. Read More