M. P. Aubry

Bio: M. P. Aubry is an academic researcher from CNET. The author has contributed to research in topics: Magnetopause. The author has an hindex of 1, co-authored 1 publications receiving 951 citations.

Satellite studies of magnetospheric substorms on August 15, 1968. IX - Phenomenological model for substorms.

Abstract: Observations made during three substorms on August 15, 1968, are shown to be consistent with current theoretical ideas about the cause of substorms. The phenomenological model described in several preceding papers is further expanded. This model follows closely the theoretical ideas presented more quantitatively in recent papers by Coronti and Kennel (1972 and 1973).

The THEMIS Mission

Abstract: The Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is the fifth NASA Medium-class Explorer (MIDEX), launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. The mission employs five identical micro-satellites (hereafter termed “probes”) which line up along the Earth’s magnetotail to track the motion of particles, plasma and waves from one point to another and for the first time resolve space–time ambiguities in key regions of the magnetosphere on a global scale. The probes are equipped with comprehensive in-situ particles and fields instruments that measure the thermal and super-thermal ions and electrons, and electromagnetic fields from DC to beyond the electron cyclotron frequency in the regions of interest. The primary goal of THEMIS, which drove the mission design, is to elucidate which magnetotail process is responsible for substorm onset at the region where substorm auroras map (∼10 RE): (i) a local disruption of the plasma sheet current (current disruption) or (ii) the interaction of the current sheet with the rapid influx of plasma emanating from reconnection at ∼25 RE. However, the probes also traverse the radiation belts and the dayside magnetosphere, allowing THEMIS to address additional baseline objectives, namely: how the radiation belts are energized on time scales of 2–4 hours during the recovery phase of storms, and how the pristine solar wind’s interaction with upstream beams, waves and the bow shock affects Sun–Earth coupling. THEMIS’s open data policy, platform-independent dataset, open-source analysis software, automated plotting and dissemination of data within hours of receipt, dedicated ground-based observatory network and strong links to ancillary space-based and ground-based programs. promote a grass-roots integration of relevant NASA, NSF and international assets in the context of an international Heliophysics Observatory over the next decade. The mission has demonstrated spacecraft and mission design strategies ideal for Constellation-class missions and its science is complementary to Cluster and MMS. THEMIS, the first NASA micro-satellite constellation, is a technological pathfinder for future Sun-Earth Connections missions and a stepping stone towards understanding Space Weather.

Neutral line model of substorms: Past results and present view

Abstract: The near-Earth neutral line (NENL) model of magnetospheric substorms is reviewed. The observed phenomenology of substorms is discussed including the role of coupling with the solar wind and interplanetary magnetic field, the growth phase sequence, the expansion phase (and onset), and the recovery phase. New observations and modeling results are put into the context of the prior model framework. Significant issues and concerns about the shortcomings of the NENL model are addressed. Such issues as ionosphere-tail coupling, large-scale mapping, onset trigger- ing, and observational timing are discussed. It is concluded that the NENL model is evolving and being improved so as to include new observations and theoretical insights. More work is clearly required in order to incorporate fully the complete set of ionospheric, near-tail, midtail, and deep- tail features of substorms. Nonetheless, the NENL model still seems to provide the best avail- able framework for ordering the complex, global manifestations of substorms.

The Magnetospheric Multiscale Magnetometers

Abstract: The success of the Magnetospheric Multiscale mission depends on the accurate measurement of the magnetic field on all four spacecraft. To ensure this success, two independently designed and built fluxgate magnetometers were developed, avoiding single-point failures. The magnetometers were dubbed the digital fluxgate (DFG), which uses an ASIC implementation and was supplied by the Space Research Institute of the Austrian Academy of Sciences and the analogue magnetometer (AFG) with a more traditional circuit board design supplied by the University of California, Los Angeles. A stringent magnetic cleanliness program was executed under the supervision of the Johns Hopkins University’s Applied Physics Laboratory. To achieve mission objectives, the calibration determined on the ground will be refined in space to ensure all eight magnetometers are precisely inter-calibrated. Near real-time data plays a key role in the transmission of high-resolution observations stored on board so rapid processing of the low-resolution data is required. This article describes these instruments, the magnetic cleanliness program, and the instrument pre-launch calibrations, the planned in-flight calibration program, and the information flow that provides the data on the rapid time scale needed for mission success.

Large‐scale characteristics of field‐aligned currents associated with substorms

Abstract: Characteristics of field-aligned currents have been determined during a large number of substorms from the magnetic field observations acquired with the Triad satellite. The statistical features of field-aligned currents include the following: (1) The large-scale regions of field-aligned currents determined previously by the authors (Iijima and Potemra, 1976a) persist during all phases of substorm activity, namely, region 1, located near the poleward boundary of the field-aligned current region, and region 2, located near the equatorward boundary. Field-aligned currents flow into region 1 on the morningside and away from region 1 on the eveningside. The current flow in region 2 is reversed to region 1 at any given local time except in the Harang discontinuity region (∼2000–2400 MLT), where the flow patterns are more complicated. (2) During active periods (|AL| ≥ 100 γ) the average latitude width of regions 1 and 2 increases by 20–30%, and the centers of these regions shift equatorward by 2°–3° with respect to the quiet time values. (3) The current density in region 1 is statistically larger than the current density in region 2 at all local times except during active periods and in the midnight to morning local time sector. In this region, where the westward electrojet is most active, the current density in region 2 can exceed the current density in region 1. (4) During relatively quiet conditions (|AL| < 100 γ) the largest field-aligned current densities occur in two areas of region 1 near noon (near ∼ 1030 MLT and ∼ 1300 MLT) with an average value of ∼1.6µA/m². During active periods (|AL| ≥ 100 γ) the regions of peak current density shift toward the nightside (the region near 1030 MLT shifts to ∼0730 MLT, and the region near ∼1300 MLT shifts to ∼1430 MLT), and the average current density increases to ∼2.2 µA/m². (5) The average total amount of field-aligned current flowing into the ionosphere always equals the current flow away from the ionosphere during a wide range of quiet and disturbed conditions. The average total current during quiet periods is ∼2.7 × 106 A and during disturbed periods is ∼5.2 × 106 A. (6) A three-region pattern of field-aligned current flow persists in the Harang discontinuity region (∼2000–2400 MLT) during undisturbed and disturbed periods, when the westward auroral electrojet does not intrude into this sector. This flow pattern consists of an upward flowing field-aligned current surrounded to the north and south by downward flowing currents. During periods when the westward auroral electrojet has intruded deeply into the evening sector the Triad magnetometer data exhibit complicated and fine-structured variations indicating the presence of complex field-aligned currents in this sector. (7) The alignment of current sheets is generally along the boundary of the auroral oval (rather than in the east-west direction), but noticeable distortions of this alignment occur during very disturbed periods. The alignment of field-aligned currents is different in region 1 and region 2 during active periods. The different behavior of field-aligned currents in region 1 and 2 during substorms actively suggests that they are controlled by different source regions in the magnetosphere or ionosphere. The region 1 field-aligned currents map to the outermost part of the magnetosphere and magnetotail region, whereas the region 2 currents map to regions of the plasma sheet closer to the earth.

Current disruption in the Earth's magnetosphere: Observations and models

Abstract: Observations and models of current disruption in the Earth's magnetosphere are briefly reviewed. At the approach of current disruption onset, the cross-tail current sheet shows a rapid growth in the current density, a large upsurge in the duskward ion bulk speed to nearly the ion thermal speed, an increase in the plasma pressure and its isotropy, a rise in the plasma beta, and a decrease in the current sheet thickness to a length scale comparable to the thermal ion gyroradius. During current disruption, there are (1) large changes in the local magnetic and electric fields, (2) significant magnetic and electric fluctuations over a broad frequency range, (3) magnetic field-aligned counterstreaming electron beams, (4) ion energization perpendicular to the magnetic field, and (5) reduction in the cross-tail current by an amount similar to that built up during the growth phase. Observations further indicate that regions of local reversal of the north-south magnetic field component are not necessarily sites of intense particle energization. Remote sensing of disruption activities shows that at least some current disruptions are not caused by a disturbance propagating earthward from the tail beyond 10 RE downstream. The timescale involved is comparable to or shorter than the ion gyroperiod. Current disruption thus has spatial and temporal scales outside the MHD regime. Several models for current disruption are briefly discussed. Two roles are considered for the cross-field current instability proposed for current disruption. It can provide anomalous resistivity for magnetic reconnection as advocated by the traditional viewpoint or act singly to instigate global changes of the magnetosphere during the initial substorrn expansion phase. The latter role is elaborated by showing that the instability may modify significantly the local current density and any such process will alter the force equilibrium in the current sheet and give rise to an efficient plasma and energy transport on a global scale. Furthermore, such a process can generate field-aligned current with intensity comparable to those associated with an auroral breakup arc at substorrn expansion onset. This scenario leads to a new emphasis that in addition to magnetic reconnection, rapid conversion of magnetic energy into particle energy in magnetotail systems may take place without a magnetic X line or separatrix playing the key role in energy conversion.