Fig 5 - uploaded by Donald Mitchell
Content may be subject to copyright.
Contour of the azimuthal current density in the meridional plane at 03 MLT (approximate local time of the pressure peak in Figure 1). The unit of the current density contours is nA m −2 .
Source publication
The global ion distributions extracted from ENA images measured by IMAGE/HENA can be used to calculate the plasma pressure. In principle, knowing the plasma-pressure distribution and the magnetic field, one can also calculate the three-dimensional current system that is driven by the pressure gradient. The currents depend on the pressure gradient a...
Context in source publication
Context 1
... is reasonable to expect that including the higher energy protons (>60 keV) will extend the FACs through dusk, since higher energy ions drift further around due to the energy dependence of the magnetic drift. Figure 5 shows the azimuthal current density in the meridional at φ=225 • (03 MLT), which correspond to a cut through the pressure peak in Figure 1. The figure is presented in the same format as Figure 9 in T2000. ...
Similar publications
In this paper we propose a new optimization principle for defining rotational curves
(partial barriers) which best approximate rotational invariant curves in area-preserving twist
maps, based on the concept of mean-square-flux minimization. Rather than constraining
partial barriers to contain orbits, as in previous work, we simply specify a pair...
Citations
... In addition to carrying spectral and directional information of the energetic ions, the ENAs also provide direct measurement of their species composition. In the Earth's magnetosphere the ring current charge-exchanges with the geocorona at high altitudes, emitting ENAs that allow the ring current and plasma sheet ion populations to be imaged (Roelof et al. 2004). ...
How does solar wind energy flow through the Earth’s magnetosphere, how is it converted and distributed? is the question we want to address. We need to understand how geomagnetic storms and substorms start and grow, not just as a matter of scientific curiosity, but to address a clear and pressing practical problem: space weather, which can influence the performance and reliability of our technological systems, in space and on the ground, and can endanger human life and health. Much knowledge has already been acquired over the past decades, particularly by making use of multiple spacecraft measuring conditions in situ, but the infant stage of space weather forecasting demonstrates that we still have a vast amount of learning to do. A novel global approach is now being taken by a number of space imaging missions which are under development and the first tantalising results of their exploration will be available in the next decade. In this White Paper, submitted to ESA in response to the Voyage 2050 Call, we propose the next step in the quest for a complete understanding of how the Sun controls the Earth’s plasma environment: a tomographic imaging approach comprising two spacecraft in highly inclined polar orbits, enabling global imaging of magnetopause and cusps in soft X-rays, of auroral regions in FUV, of plasmasphere and ring current in EUV and ENA (Energetic Neutral Atoms), alongside in situ measurements. Such a mission, encompassing the variety of physical processes determining the conditions of geospace, will be crucial on the way to achieving scientific closure on the question of solar-terrestrial interactions.
... The near-equatorial currents are also drawn, illustrating the low-latitude structure of the entire system. The figure demonstrates the model's ability to resolve both westward and eastward parts of the PRC, as well as their connection in the form of "horseshoe" or "banana" currents (Roelof et al., 2004;Liemohn et al., 2013). ...
This chapter addresses the empirical models of the terrestrial magnetosphere based on large amounts of spacecraft data from many past and present satellite missions. Unlike computer simulations, which derive the expected magnetospheric configurations by solving first‐principle equations, the data‐based models seek to reconstruct the real‐world magnetosphere from direct in situ observations and, in that sense, represent the “ground truth” of the data. The empirical models are based on three cornerstones: multiyear archives of satellite and ground data, a mathematical framework describing the magnetospheric field sources, and parametrization methods relating the model input to the solar wind drivers and/or ground‐based geomagnetic indices. Accordingly, this chapter includes three sections devoted to each of the above aspects. In conclusion, we discuss future prospects and challenges, with a particular focus on reconstructing instantaneous real‐time magnetospheric configurations, based on simultaneous data of multisatellite constellations of the geospace monitors.
... The first one comes from the nightside magnetosphere. The morphology of the three-dimensional current line is consistent with that inferred from the global imaging ofenergetic neutral atoms (Roelof et al., 2004). The latter one comes from the dayside magnetosphere, which is consistent with that previously obtained by the MHD simulation (Ebihara et al., 2014). ...
We investigated energy flow in the inner magnetosphere on the basis of the results obtained by a global magnetohydrodynamic simulation. When the magnetosphere is exposed to a southward interplanetary magnetic field, the magnetosphere undergoes quasi‐steady convection. Downward (earthward) Poynting flux is found in the polar cap, which is consistent with previous observations. However, Poynting flux appears to be upward (antiearthward) in the equatorward region of the auroral oval. The Region 2 field‐aligned current (FAC) is embedded in the upward Poynting flux region. The upward Poynting flux is closely associated with space charge deposited by the ionospheric Hall current under inhomogeneous ionospheric conductivity. The space charge gives rise to shear flow of plasma, which is transmitted upward to the magnetosphere. The shear flow generates additional Region 2 FAC, at least, in the low‐altitude magnetosphere. Spatial distribution of the Region 2 FAC appears to depend on altitude, suggesting the significant influence of the ionosphere in the Region 2 FAC region. We traced integral curves of Poynting flux (S curves) backward from a magnetic field line in the Region 2 FAC region and found that the S curves originate either in the solar wind and in the earthward‐most boundary of the simulation. These simulation results suggest that the ionosphere participates in the generation of the Region 2 FAC, and the ionosphere is a mediator to feed energy to the inner magnetosphere under the quasi‐steady convection.
... Interestingly, the shortlegged incomplete current wedge is connected to the poleward half of the Region 2-like FAC that is newly developed during the substorm expansion (Ebihara et al. 2014). This current line is consistent with the theoretically obtained one (Roelof et al. 2004). ...
Abstract A substorm is a transient phenomenon that lasts for only 1–2 h. One significant manifestation of the substorm is a sudden brightening of the aurora on the nightside. Simultaneously, the auroral electrojets are abruptly intensified in the ionosphere, disturbing the geomagnetic field in the polar region. The near-Earth space environment is highly disturbed, which manifests as an earthward fast flow of plasma, a sudden change in the magnetic field, or a sudden increase in hot plasma. Such disturbances are known to severely affect human society. The ultimate cause of the disturbances is the solar wind, but an explanation of the chain of processes leading from solar wind to the ionosphere is problematic. Here, the evolution of the auroral substorm is reviewed based on the results of a global magnetohydrodynamics (MHD) simulation, called a REProduce Plasma Universe (REPPU) code. The REPPU code is shown to reproduce many aspects of the auroral substorms and to be useful for understanding the primary chain processes from the solar wind to the ionosphere.
... In addition to carrying spectral and directional information of the energetic ions, the ENAs also provide direct measurement of their species composition. In the Earth's magnetosphere the ring current charge-exchanges with the geocorona at high altitudes, emitting ENAs that allow the ring current and plasma sheet ion populations to be imaged (Roelof et al. 2004). ...
This paper addresses the fundamental science question: "How does solar wind energy flow through the Earth's magnetosphere, how is it converted and distributed?". We need to understand how the Sun creates the heliosphere, and how the planets interact with the solar wind and its magnetic field, not just as a matter of scientific curiosity, but to address a clear and pressing practical problem: space weather, which can influence the performance and reliability of our technological systems, in space and on the ground, and can endanger human life and health. Much knowledge has already been acquired over the past decades, but the infant stage of space weather forecasting demonstrates that we still have a vast amount of learning to do. We can tackle this issue in two ways: 1) By using multiple spacecraft measuring conditions in situ in the magnetosphere in order to make sense of the fundamental small scale processes that enable transport and coupling, or 2) By taking a global approach to observations of the conditions that prevail throughout geospace in order to quantify the global effects of external drivers. A global approach is now being taken by a number of space missions under development and the first tantalising results of their exploration will be available in the next decade. Here we propose the next step-up in the quest for a complete understanding of how the Sun gives rise to and controls the Earth's plasma environment: a tomographic imaging approach comprising two spacecraft which enable global imaging of magnetopause and cusps, auroral regions, plasmasphere and ring current, alongside in situ measurements. Such a mission is going to be crucial on the way to achieve scientific closure on the question of solar-terrestrial interactions.
... Ebihara et al. (2002) examined L-MLT distributions near the equatorial plane of proton energy density in the energy range of 1-200 keV for storm stages, using data from the Polar satellite; they found a strong day-night asymmetry in energy density during the main phase. Energetic neutral atom imaging on board the Imager for Magnetopause-to-Aurora Global Exploration satellite captured the global plasma pressure distribution at a specific time, although the energy range (10-120 keV) and spatial resolution were limited (C:son Roelof, 1989;Roelof et al., 2004). Recently, Yue et al. (2018) conducted a comprehensive study of the L-MLT distribution of plasma pressures for each species, energy range, and AE index level using data from the Van Allen Probes. ...
We examined the average meridional distribution of middle‐energy protons (10–180 keV) and pressure‐driven currents in the nightside (20–04 hr magnetic local time) ring current region during moderately disturbed times using the Arase satellite's data. Because the Arase satellite has a large inclination orbit of 31°, it covers the magnetic latitude (MLAT) in the range of −40° to 40° and a radial distance of <6RE. We found that the plasma pressure decreased significantly with increasing MLAT. The plasma pressure on the same L* shell at 30° < MLAT < 40° was ∼10–60% of that at 0° < 4 MLAT < 10°, and the rate of decrease was larger on lower L* shells. The pressure anisotropy, derived as the perpendicular pressure divided by the parallel pressure minus 1, decreased with radial distance and showed a weak dependence on MLAT. The magnitude of the plasma beta at 30°<MLAT<40° was 1 or 2 orders smaller than that at 0°<MLAT<10°. The plasma pressure normalized by the value at 0°<MLAT<10° estimated from the magnetic strength and anisotropy was roughly consistent with the observed plasma pressure for L*=3.5–5.5. The azimuthal pressure‐gradient current derived from the plasma pressure was distributed over MLAT∼0–20° , while the curvature current was limited within MLAT∼0–10° . We suggest that the latitudinal dependence should be taken into account in interpretations of plasma parameters in successive orbits during magnetic storms.
... In addition to carrying spectral and directional information of the energetic ions, the ENAs also provide direct measurement of their species composition. In the Earth's magnetosphere the ring current charge-exchanges with the geocorona at high altitudes, emitting ENAs that allow the ring current and plasma sheet ion populations to be imaged (Roelof et al. 2004). ...
This paper addresses the fundamental science question: "How does solar wind energy flow through the Earth's magnetosphere, how is it converted and distributed?". We need to understand how the Sun creates the heliosphere, and how the planets interact with the solar wind and its magnetic field, not just as a matter of scientific curiosity, but to address a clear and pressing practical problem: space weather, which can influence the performance and reliability of our technological systems, in space and on the ground, and can endanger human life and health. Much knowledge has already been acquired over the past decades, but the infant stage of space weather forecasting demonstrates that we still have a vast amount of learning to do. We can tackle this issue in two ways: 1) By using multiple spacecraft measuring conditions in situ in the magnetosphere in order to make sense of the fundamental small scale processes that enable transport and coupling, or 2) By taking a global approach to observations of the conditions that prevail throughout geospace in order to quantify the global effects of external drivers. A global approach is now being taken by a number of space missions under development and the first tantalising results of their exploration will be available in the next decade. Here we propose the next step-up in the quest for a complete understanding of how the Sun gives rise to and controls the Earth's plasma environment: a tomographic imaging approach comprising two spacecraft which enable global imaging of magnetopause and cusps, auroral regions, plasmasphere and ring current, alongside in situ measurements. Such a mission is going to be crucial on the way to achieve scientific closure on the question of solar-terrestrial interactions.
... Subsequently, energized ions become the dominant source of plasma pressure in the inner magnetosphere. Hot plasma pressure drives large electric currents which determine global electrodynamics and coupling of the inner magnetosphere-ionosphere system [e.g., Roelof et al., 2004]. Pressure-driven currents can cause large distortions of magnetic field across the inner magnetosphere leading to rapid magnetopause loss of relativistic electrons from the outer radiation belts [e.g., Ukhorskiy et al., 2006]. ...
Transport and acceleration of ions in the magnetotail largely occurs in
the form of discrete impulsive events associated with a steep increase
of the tail magnetic field normal to the neutral plane (Bz),
which are referred to as dipolarization fronts. The goal of this paper
is to investigate how protons initially located upstream of earthward
moving fronts are accelerated at their encounter. According to our
analytical analysis and simplified two-dimensional test-particle
simulations of equatorially mirroring particles, there are two regimes
of proton acceleration: trapping and quasi-trapping, which are realized
depending on whether the front is preceded by a negative depletion in
Bz. We then use three-dimensional test-particle simulations
to investigate how these acceleration processes operate in a realistic
magnetotail geometry. For this purpose we construct an analytical model
of the front which is superimposed onto the ambient field of the
magnetotail. According to our numerical simulations, both trapping and
quasi-trapping can produce rapid acceleration of protons by more than an
order of magnitude. In the case of trapping, the acceleration levels
depend on the amount of time particles stay in phase with the front
which is controlled by the magnetic field curvature ahead of the front
and the front width. Quasi-trapping does not cause particle scattering
out of the equatorial plane. Energization levels in this case are
limited by the number of encounters particles have with the front before
they get magnetized behind it.
... If the plasma pressure P distribution and the magnetic field B are known, the three-dimensional current system driven by the pressure gradients can be computed. This was done in Roelof et al. (2004), who used ENA images from the IMAGE HENA instrument that were inverted using a constrained linear inversion (DeMajistre et al., 2004) to obtain the proton distribution functions (Brandt et al., 2002b). It is possible then to compute the partial pressure over the energy range of ENA hydrogen measured by HENA. ...
... It is also possible to calculate the field-aligned current flowing into the ionosphere according to Vasyliunas (1984). Roelof et al. (2004) computed the 3-D current system using an Euler potential formalism following Roelof (1989). A dipole magnetic field and an isotropic pressure were assumed. ...
... The second Euler potential Q for a dipole field satisfies B × ∇Q = 1, so Q is the partial volume of the flux tube (Q = 0 at the magnetic minimum-B equator). As was shown in Roelof et al. (2004) and Brandt et al. (2002a), the peak of the partial pressure occurs in the postmidnight sector. ...
Electric currents flowing through geospace support a highly nondipolar
magnetic field topology, and their time-varying dynamics change particle
drift paths and create a nonlinear feedback on the currents themselves.
A number of current systems exist in the magnetosphere, most commonly
the dayside magnetopause Chapman-Ferraro currents, high latitude "region
1" field-aligned Birkeland currents, lower-latitude "region 2"
field-aligned currents connected to the partial ring current,
magnetotail currents, and the symmetric ring current. In the near-Earth
nightside, however, several of these current systems flow in close
proximity to each other and it is very difficult to identify a local
measurement as belonging to a specific system. Such identification is
important, however, because how the current closes and how these loops
change in space and time governs the magnetic topology of the
magnetosphere and therefore controls the physical processes of geospace.
Furthermore, many methods exist for identifying the regions of
near-Earth space carrying each type of current. This study presents a
robust collection of these definitions of current systems in geospace,
particularly in the near-Earth nightside magnetosphere, as viewed from a
variety of observational and computational analysis techniques. The
influence of definitional choice on the resulting interpretation of
physical processes governing geospace dynamics is presented and
discussed.
... Two methods have been developed in order to calculate the current density: the method of the pressure gradient, which uses the plasma fluid momentum equation (Lui et al., 1987;Roelof et al., 2004), and the curlometer technique, which uses the Maxwell-Ampere law (Robert and Roux, 1993;Robert et al., 1998a;Dunlop et al., 2002;Dunlop and Balogh, 1993). The first method requires the determination of pressure gradients, which is quite difficult using satellite data. ...
Knowledge of the inner magnetospheric current system (intensity,
boundaries, evolution) is one of the key elements for the understanding
of the whole magnetospheric current system. In particular, the
calculation of the current density and the study of the changes in the
ring current is an active field of research as it is a good proxy for
the magnetic activity. The curlometer technique allows the current
density to be calculated from the magnetic field measured at four
different positions inside a given current sheet using the
Maxwell-Ampere's law. In 2009, the CLUSTER perigee pass was located at
about 2 RE allowing a study of the ring current deep inside
the inner magnetosphere, where the pressure gradient is expected to
invert direction. In this paper, we use the curlometer in such an orbit.
As the method has never been used so deep inside the inner
magnetosphere, this study is a test of the curlometer in a part of the
magnetosphere where the magnetic field is very high (about 4000 nT) and
changes over small distances (ΔB = 1nT in 1000 km). To do so, the
curlometer has been applied to calculate the current density from
measured and modelled magnetic fields and for different sizes of the
tetrahedron. The results show that the current density cannot be
calculated using the curlometer technique at low altitude perigee
passes, but that the method may be accurate in a [3 RE; 5
RE] or a [6 RE; 8.3 RE] L-shell range.
It also demonstrates that the parameters used to estimate the accuracy
of the method are necessary, but not sufficient conditions.
