We elaborate upon the leakage model for the escape of energetic magnetospheric particles into the magnetosheath. Unlike the merging model, no interconnection (or merging) of magnetospheric and magnetosheath magnetic field lines is required. Because outer magnetospheric energetic particle drift paths intersect the magnetopause, the leakage model requires the continual escape of ions at postnoon local times and electrons at prenoon local times, regardless of solar wind conditions. It also predicts a division between dawnward and duskward streaming ions at the point where most magnetosheath magnetic field lines make their closest approach to the magnetopause, typically near 1500 LT. Like the merging model, the leakage model predicts equatorward streaming just inside the magnetopause. We study the motion of an escaping energetic ion at a planar magnetopause to show that, without scattering, ions must move dawnward and northward in a duskward magnetosheath magnetic field and dawnward and southward in a dawnward magnetosheath magnetic field. Scattering permits some ions to move duskward. We present new observations of streaming ions outside the dayside magnetopause made by the Charge Composition Explorer satellite, a part of the Active Magnetospheric Particle Tracer Explorers program. To place these observations in context, we have performed a statistical study of previous particle observations both inside and outside the dayside magnetopause. The ensemble of observations indicates that energetic magnetospheric ions of all species continually escape from the dayside magnetosphere and stream along magnetosheath magnetic field lines, even when no merging is expected. The magnetosheath magnetic field controls the direction in which the ions stream: they move away from the magnetosphere. The results of this work indicate that energetic particle observations at the dayside magnetopause need not be taken as evidence for merging of magnetosheath and magnetospheric magnetic field lines. 12,097 12,098 SIBECK ET AL.: ENERGETIC MAGNETOSPHERIC IONS AT THE DAYSIDE MAGNETOPAUSE
Abstract. We investigate the ion composition of the near-Earth plasma sheet in storm and quiet intervals, using energetic (9-210 keV) particle flux data obtained by the suprathermal ion composition spectrometer (STICS) sensor of the energetic particle and ion composition (EPIC) instrument on the Geotail spacecraft. In 1998 four magnetic storms (minimum Dst(-50 nT) occurred when Geotail was located in the near-Earth plasma sheet (X_•-10 RE). For each of the storms, we have
Abstract.The scientific ascent of humankind comes in two forms: incremental progress with traditional thinking, and paradigm transition. The latter typically engenders intense debate, often long lasting, before the transition of the paradigm is deemed acceptable. The magnetospheric discipline is no exception, especially in view of the sparse observations available to reach conclusive theory-data closure. Scientific controversies serve an important role in identifying significant unresolved issues for progress to be made. This review highlights key issues on four controversies present in magnetospheric physics: (1) the on-and-off debate on whether the magnetic field combined with the plasma bulk flow or the electric field combined with the current density is the primary quantity in treating magnetospheric problems; (2) the proper interpretation of transient dayside magnetospheric phenomena, i.e., whether they are related to flux transfer events, plasma transfer events, or solar wind pressure pulses; (3) the physical processes responsible for substorm onset; and (4) justifications for substorms or enhanced magnetospheric convection as the cause of magnetic storms. In issue 1 the merits and limitations of the two approaches are expounded. In issue 2 the predicted similarities and differences between the three interpretations are summarized. In issue 3 the strengths and weaknesses of prominent existing substorm models are elaborated on. In issue 4 the two contributors to storms are recognized and combined. Each controversy has an element of a paradigm transition. The resolutions of these controversies appear to also have one common element in that the presumption of only one theory to be correct may not be valid; a synthesis of existing theories may provide a better understanding of all features associated with the phenomenon. INTRODUCTIONSpace is our final frontier for exploration. Over the past 4 decades of space exploration, initiated by the launch of Sputnik in 1957, thousands of man-made satellites were hurled into space to make both in situ and remote sensing measurements. Technological assets in space are accumulating at an ever-accelerating pace. Our society has also grown substantially dependent on these space technologies for daily routine functions, such as in the areas of communication, navigation, and global monitoring of atmospheric weather. Space weather is emerging to become a practical concern as adverse space disturbances start to impact our daily activities. Although space travel envisioned in the famous science fiction movie 2001: A Space Odyssey has not materialized, the day will come, perhaps in this century, when commercial flights to other planets and moons of our solar system become commonplace. The importance of nowcasting and forecasting space weather for space travelers will then be parallel to that of atmospheric weather for globe-trotters today. Indeed, space tourism has already started, with Dennis Tito as the first space tourist.Over 99
Measurements of plasma and energetic electrons made during substorms by Vela satellites within ≲1 RE of the magnetotail neutral sheet are reported. Rapid antisunward flow of plasma is observed to start at the onset of the expansion phase of a substorm (i.e., at breakup) and to continue until the expansion phase ends and substorm recovery begins, as is indicated by auroral zone magnetograms. When substorm recovery begins, the plasma flow reverses direction, and rapid sunward flow begins. Fluxes of energetic electrons are low, and the temperature of the plasma is reduced during the interval of antisunward flow. The lowest fluxes (i.e., complete dropouts) of energetic electrons are observed just before the reversal of plasma flow to the sunward direction. After the reversal the energetic electron flux intensity rises rapidly to high values as the plasma sheet recovers. These observations are regarded as added evidence that a neutral line forms between the earth and the Vela orbit (r ≈ 18 RE) at substorm breakup and then moves suddenly to distances beyond the Vela orbit when substorm recovery starts. Throughout the expansive phase there exists a thin residual plasma sheet beyond the neutral line in which plasma continually flows rapidly downstream into the more distant tail. The particle dropout just preceding the flow reversal and plasma sheet recovery is thought to be the signature of the passage of the neutral line near the Vela satellite as it moves rapidly outward in the tail. Spin modulation of the proton flux observed continuously for about 1 hour during very quiet conditions preceding one substorm may constitute a direct measurement of the proton component of the cross‐tail electric current that maintains the taillike configuration of the magnetotail field.
O+1 and N+1 are important ring current ions in great magnetic storms. We study ∼10–210 keV/e O+1 and N+1 in dayside outer ring current (ORC) at ∼9–15 RE using Geotail's EPIC/STICS ion spectrometer. We find: average N+1/O+1 (ΓN/O) varies by ∼2 over a solar cycle, ∼40% (∼20%) at solar minimum (maximum); individual ΓN/O values range from ∼0.15 (moderate solar maximum storm) to ∼1 (18‐hr solar minimum superquiet interval); and N+1 is third in importance after H+ and O+1 during two moderate storms (Dstmin ∼ −80 nT, ∼25% great storm intensity), one at minimum, one maximum. High‐latitude topside ionospheric AE‐D/MIMS ion composition data form a baseline reference used to argue that ORC ΓN/O variations generally reflect and may be partially explained by topside ionospheric density ΓN/O spatial variations.
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