Magnetotail flow bursts: Association to global magnetospheric circulation, relationship to ionospheric activity and direct evidence for localization (original) (raw)
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Joint observations by Cluster satellites of bursty bulk flows in the magnetotail
Journal of Geophysical Research, 2006
1] Using the observations of three satellites of Cluster (C1, C3, and C4) during the periods we study 209 active time bursty bulk flows (BBFs), the difference between single satellite observations and multisatellite observations, and the difference among three selection criteria (two about BBFs and one about rapid convection event). Single satellite observations show that the average duration of BBFs selected by the criterion of Angelopoulos et al. is 604 s, while multisatellite observations show that the average duration of BBFs is 1105 s. Single satellite sometimes misses the BBFs. The missing ratio of single satellite is 22.4% for the criterion of Angelopoulos et al. and 44.9 % for the criterion of Raj et al. Therefore the single satellite observations cannot tell the true number of BBFs. The multisatellite observations are more important for the criterion of Raj et al. The single satellite observations also show that 22% of substorms are not accompanied by BBFs, while multisatellite observations show that only 4.5% of substorms are not accompanied by BBFs.
Journal of Geophysical Research, 1985
the summer polar cap during periods when B z > 0 have revealed a stable well-developed "W" pattern in the transverse component of/• and in the orbit parallel component of oe (Iijima et at., 1984; Burke et at. , 1979). This W pattern found in/• and oe characterizes a four-cetted ion drift pattern having sunward flow in the central polar cap flanked by regions of antisunward flow that reverses to sunward once again at lower latitudes. Subsequent investigation of electric and magnetic fields from the S3-2 and Magsat data sets shows that in the summer hemisphere a transition from this W shape into a more structured pattern occurs near the magentic dawn-dusk meridian. Since, on a seasonal basis, Magsat's orbit remained fixed with respect to the terminator, the conductivity distribution beneath the orbit track was essentially constant from one orbit to the next. Thus, this effect is not due to conductivity variations. In the winter polar cap the W pattern is difficult to identify in the measurements of the transverse component of/• or oe made on either side of magnetic dawn-dusk; however, analysis of the radial component of/• measured in both polar caps at, or tailward of, the dawn-
2022
The magnetotail earthward fast flow bursts can transport most of the magnetic flux and energy into the inner magnetosphere. These fast flow bursts are generally an order of magnitude higher than the typical convection speeds, that are azimuthally localized (1-3RE) and are flanked by plasma vortices which map to ionospheric plasma vortices of the same sense of rotation. This study uses multipoint analysis of conjugate magnetospheric and ionospheric observations to investigate the magnetospheric and ionospheric responses to the fast flow bursts that are associated with both substorms and pseudobreakups. We study in detail what properties control the differences in the magnetosphere-ionosphere responses between substorm and pseudobreakup conditions, and how such differences lead to the different ionospheric responses. The fast flow bursts and pseudobreakup events were observed by the Time History of Events and Macroscale Interaction during Substorms (THEMIS), when the satellites were at least 6RE from the Earth in radial distance, and a magnetic local time (MLT) region of ±5 hours from local midnight. The results show that the magnetosphere and ionosphere response to substorm fast flow bursts are much stronger and more structured compared to pseudobreakups, which is more likely to be localized, transient, and weak in the magnetosphere. The magnetic flux in the tail is much stronger for strong substorms and much weaker for pseudobreakup events. The B lobe decreases significantly for substorm fast flow bursts compared to pseudobreakup events. The curvature force density for pseudobreakups are much smaller than substorm fast flow events, indicating that the pseudobreakups may not be able to penetrate deep into the inner magnetosphere. This association can help us study the properties and activity of the magnetospheric earthward flow vortices from ground data.
Survey of cold ionospheric outflows in the magnetotail
Annales Geophysicae, 2009
Low-energy ions escape from the ionosphere and constitute a large part of the magnetospheric content, especially in the geomagnetic tail lobes. However, they are normally invisible to spacecraft measurements, since the potential of a sunlit spacecraft in a tenuous plasma in many cases exceeds the energy-per-charge of the ions, and little is therefore known about their outflow properties far from the Earth. Here we present an extensive statistical study of cold ion outflows (0-60 eV) in the geomagnetic tail at geocentric distances from 5 to 19 R E using the Cluster spacecraft during the period from 2001 to 2005. Our results were obtained by a new method, relying on the detection of a wake behind the spacecraft. We show that the cold ions dominate in both flux and density in large regions of the magnetosphere. Most of the cold ions are found to escape from the Earth, which improves previous estimates of the global outflow. The local outflow in the magnetotail corresponds to a global outflow of the order of 10 26 ions s −1. The size of the outflow depends on different solar and magnetic activity levels.
Annales Geophysicae, 2005
An extensive variety of instruments, including Geotail, DMSP F11, SuperDARN, and IMP-8, were monitoring the dayside magnetosphere and ionosphere between 14:00 and 18:00 UT on 18 January 1999. The location of the instruments provided an excellent opportunity to study in detail the direct coupling between the solar wind, the magnetosphere, and the ionosphere. Flux transfer events were observed by Geotail near the magnetopause in the dawn side magnetosheath at about 4 magnetic local time during exclusively northward interplanetary magnetic field conditions. Excellent coverage of the entire dayside high-latitude ionosphere was achieved by the Northern Hemisphere Su-perDARN radars. On the large scale, temporally and spatially, the dayside magnetosphere convection remained directly driven by the interplanetary magnetic field, despite the highly variable interplanetary magnetic field conditions, including long periods of northward field. The SuperDARN radars in the dawn sector also measured small-scale temporally varying convection velocities, which are indicative of flux transfer event activity, in the vicinity of the magnetic footprint of Geotail. DMSP F11 in the Southern Hemisphere measured typical cusp precipitation simultaneously with and magnetically conjugate to a single flux transfer event signature detected by Geotail. A study of the characteristics of the DMSP ion spectrogram revealed that the source plasma from the reconnection site originated downstream of the subsolar point. Detailed analyses of locally optimised coordinate systems for individual flux transfer events at Geotail are consistent with a series of flux tubes protruding from the magnetopause, and originating from a high-latitude reconnection site in the Southern Hemisphere. This high-latitude reconnection site agrees with plasma injected away from the sub-Correspondence to: K. A. McWilliams (mcwilliams@dansas.usask.ca) solar point. This is the first simultaneous and independent determination from ionospheric and space-based data of the location of magnetic reconnection.
Multiple conjugate observations of magnetospheric fast flow bursts using THEMIS observations
Annales Geophysicae
Magnetotail earthward fast flow bursts can transport most magnetic flux and energy into the inner magnetosphere. These fast flow bursts are generally an order of magnitude higher than the typical convection speeds that are azimuthally localised (1-3 R E) and are flanked by plasma vortices, which map to ionospheric plasma vortices of the same sense of rotation. This study uses a multipoint analysis of conjugate magnetospheric and ionospheric observations to investigate the magnetospheric and ionospheric responses to fast flow bursts that are associated with both substorms and pseudobreakups. We study in detail what properties control the differences in the magnetosphere-ionosphere responses between substorm fast flow bursts and pseudobreakup events, and how these differences lead to different ionospheric responses. The fast flow bursts and pseudobreakup events were observed by the Time History of Events and Macroscale Interaction during Substorms (THEMIS), while the primary ionospheric observations were made by all-sky cameras and magnetometer-based equivalent ionospheric currents. These events were selected when the satellites were at least 6 R E from the Earth in radial distance and a magnetic local time (MLT) region of ± 5 h from local midnight. The results show that the magnetosphere and ionosphere responses to substorm fast flow bursts are much stronger and more structured compared to pseudobreakups, which are more likely to be localised, transient and weak in the magnetosphere. The magnetic flux in the tail is much stronger for strong substorms and much weaker for pseudobreakup events. The B lobe decreases significantly for substorm fast flow bursts compared to pseudobreakup events. The curvature force density for pseudobreakups are much smaller than substorm fast flow events, indicating that the pseudobreakups may not be able to penetrate deep into the inner magnetosphere. This association can help us study the properties and activity of the magnetospheric earthward flow vortices from ground data.
Journal of Geophysical Research, 1998
Two upstream solar wind pressure discontinuities that were associated with storm sudden commencements have been examined to determine their effect on the geomagnetic tail lobe field. During the two events, occurring on March 9, 1995, and August 17, 1995, the Wind spacecraft was located in the upstream region monitoring the solar wind, and the IMP 8 spacecraft was in the geomagnetic tail lobe observing the tail response. The two events occurred during periods with northward or weak southward interplanetary magnetic field. In each case, the data suggest that the magnetic field in the tail lobe increased in magnitude directly in response to the external solar wind pressure increase. It is shown that a simple model in which a uniform magnetic field is compressed by a step function constriction accurately predicts characteristic timesca!es, which are of the order of a couple minutes, and the magnetic field profiles. The inferred flaring angles are COnsistent with model predictions, and the changes in the flaring angle across the discontinuities correspond to expectations based on changes in the subsolar magnetopause position and tail width. Overall, the results of this study indicate that the magnetotail maintains an approximate MHD equilibrium even as it responds rapidly to interplanetary pressure discontinuities. 1. Introduction Geomagnetic sudden commencements are observed as rapid perturbations in magnetic fields measured at low-latitude observatories of the order of 1-6 min and with magnitudes of several tens of nanotesla [Jursa, 1985]. They are produced by the passage of a solar wind pressure discontinuity or shock and its associated magnetospheric compression. The resulting sudden changes in geomagnetic field strength are observed throughout the magnetosphere, including in the magnetotail lobe [Kawano et al., 1992] where a "sudden increase" in the lobe magnetic field strength is observed [Sugiura et al., 1968] because of the magnetotail compression caused by the pressure enhancement. Currently, in the International Solar Terrestrial Physics (ISTP) era it is possible to study the effect of these pressure discontinuities on the tail lobes routinely by using multiple spacecraft. This study employs data from the IMP 8 and Wind spacecraft when Wind was in the upstream region monitoring the solar wind and observed a solar wind pressure increase and when IMP 8 was in the tail lobe. To avoid complications potentially introduced by the response of the lobe magnetic field strength to a southward interplanetary magnetic field (IMF)
A survey of magnetopause FTEs and associated flow bursts in the polar ionosphere
Annales Geophysicae, 2000
Using the Equator-S spacecraft and Super-DARN HF radars an extensive survey of bursty reconnection at the magnetopause and associated¯ows in the polar ionosphere has been conducted. Flux transfer event (FTE) signatures were identi®ed in the Equator-S magnetometer data during periods of magnetopause contact in January and February 1998. Assuming the eects of the FTEs propagate to the polar ionosphere as geomagnetic ®eld-aligned-currents and associated Alfve n-waves, appropriate ®eld mappings to the ®eldsof-view of SuperDARN radars were performed. The radars observed discrete ionospheric¯ow channel events (FCEs) of the type previously assumed to be related to pulse reconnection. Such FCEs were associated with 80% of the FTEs and the two signatures are shown to be statistically associated with greater than 99% con®dence. Exemplary case studies highlight the nature of the ionospheric¯ows and their relation to the high latitude convection pattern, the association methodology, and the problems caused by instrument limitations.
Advances in Space Research, 1997
Observations from the GEOTAIL spacecraft are used to examine the plasma flow and magnetic field within the magnetosheath at intermediate downtail distances. Simultaneous measurements of the solar wind condition as measured by the WIND spacecraft are also used for this study. Close to the downtail magnetopause, we find that under appropriate solar wind conditions, the plasma flow velocity of the magnetosheath is slowest when the local magnetic field and velocity vectors are aligned, but are largest when the two vectors are perpendicular to one another, though the magnetosheath flow speed remains slower than or equal to the solar wind velocity. A simple model utilizing the magnetic field line tension and Alfv6n phase speed is used to explain the observations. Occasionally, close to the magnetopause we find magnetosheath flows which are much greater than the solar wind velocity, but only for certain orientations of the local magnetic field. The source of these fast plasma flows is the low latitude boundary layer (LLBL), and is not the shocked solar wind plasma. Possible reasons for the observation of very fast flows near the magnetotail magnetopause are explored.
Interball-tail observations of vertical plasma motions in the magnetotail
Annales Geophysicae, 2002
The Interball spacecraft configuration favors, in contrast to previous experiments, investigation of vertical ion flows (GSM V z ). We use measurements of the CORALL instrument for the statistical study of V z and V y plasma flows in the mid-tail plasma sheet. In agreement with the previous observations, the mean V y was positive on the dusk side and negative on the dawn side. When IMF was southward, the mean V z consisted of the convection flow towards the equatorial plane ∼ 7 km/s and the northward flow ∼ 8 km/s. When IMF was northward, both components nearly vanished. The velocity variance was much larger than the mean values. The V z variance maximized on the dawn flank and was always 15-20% smaller than the V y one. The V y variance maximized in the pre-midnight sector closer to the neutral sheet. We conclude that velocity fluctuations are composed with the inherent high-beta plasma turbulence contributing to all components, and the BBF-related activity contributing mainly to V y in the pre-midnight plasma sheet.