61 research outputs found
THEMIS Observations of Unusual Bow Shock Motion, Attending a Transient Magnetospheric Event
We present a multipoint case study of solar wind and magnetospheric observations during a transient magnetospheric compression at 2319 UT on October 15, 2008. We use high-time resolution magnetic field and plasma data from the THEMIS and GOES-11/12 spacecraft to show that this transient event corresponded to an abrupt rotation in the IMF orientation, a change in the location of the foreshock, and transient outward bow shock motion. We employ results from a global hybrid code model to reconcile the observations indicating transient inward magnetopause motion with the outward bow shock motion
Magnetospheric Cavity Modes Driven by Solar Wind Dynamic Pressure Fluctuations
We present results from Lyon-Fedder-Mobarry (LFM) global, three-dimensional
magnetohydrodynamic (MHD) simulations of the solar wind-magnetosphere
interaction. We use these simulations to investigate the role that solar wind
dynamic pressure fluctuations play in the generation of magnetospheric
ultra-low frequency (ULF) pulsations. The simulations presented in this study
are driven with idealized solar wind input conditions. In four of the
simulations, we introduce monochromatic ULF fluctuations in the upstream solar
wind dynamic pressure. In the fifth simulation, we introduce a continuum of ULF
frequencies in the upstream solar wind dynamic pressure fluctuations. In this
numerical experiment, the idealized nature of the solar wind driving conditions
allows us to study the magnetospheric response to only a fluctuating upstream
dynamic pressure, while holding all other solar wind driving parameters
constant. The simulation results suggest that ULF fluctuations in the solar
wind dynamic pressure can drive magnetospheric ULF pulsations in the electric
and magnetic fields on the dayside. Moreover, the simulation results suggest
that when the driving frequency of the solar wind dynamic pressure fluctuations
matches one of the natural frequencies of the magnetosphere, magnetospheric
cavity modes can be energized.Comment: 2 figure
Multipoint observations of compressional Pc5 pulsations in the dayside magnetosphere and corresponding particle signatures
We use Van Allen Probes (Radiation Belt Storm Probes A and B, henceforth RBSP-A and RBSP-B) and GOES-13 and GOES-15 (henceforth G-13 and G-15) multipoint magnetic field, electric field, plasma, and energetic particle observations to study the spatial, temporal, and spectral characteristics of compressional Pc5 pulsations observed during the recovery phase of a strong geomagnetic storm on 1 January 2016. From ⌠19:00 to 23:02 UT, successive magnetospheric compressions enhanced the peak-to-peak amplitudes of Pc5 waves with 4.5\u276.0 mHz frequencies from 0\u27 2 to 10\u2715 nT at both RBSP-A and RBSP-B, particularly in the prenoon magnetosphere. Poloidal Pc4 pulsations with frequencies of ⌠22\u2729 mHz were present in the radial Bx component. The frequencies of these Pc4 pulsations diminished with increasing radial distance, as expected for resonant Alfv n waves standing along field lines. The GOES spacecraft observed Pc5 pulsations with similar frequencies to those seen by the RBSP but Pc4 pulsations with lower frequencies. Both RBSP-A and RBSP-B observed frequency doubling in the compressional component of the magnetic field during the Pc5 waves, indicating a meridional sloshing of the equatorial node over a combined range in ZSM from 0.25 to-0:08 Re, suggesting that the amplitude of this meridional oscillation was ⌠0.16 Re about an equatorial node whose mean position was near ZSM D⌠0:08 Re. RBSP-A and RBSP-B HOPE (Helium Oxygen Proton Electron) and MagEIS (Magnetic Electron Ion Spectrometer) observations provide the first evidence for a corresponding frequency doubling in the plasma density and the flux of energetic electrons, respectively. Energetic electron fluxes oscillated out of phase with the magnetic field strength with no phase shift at any energy. In the absence of any significant solar wind trigger or phase shift with energy, we interpret the compressional Pc5 pulsations in terms of the mirror-mode instability
Global observations of magnetospheric highâm poloidal waves during the 22 June 2015 magnetic storm
We report global observations of highâm poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m ~ 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the singleâfrequency global poloidal modes normally observed during quiet times. Detailed examination of the instantaneous frequency reveals discrete spatial structures with stepâlike frequency changes along L. Each discrete L shell has a steady wave frequency and spans about 1 RE, suggesting that there exist a discrete number of driftâbounce resonance regions across L shells during storm times.Key PointsObserved longâlasting highâm poloidal waves associated with second harmonics of field line resonances during a major magnetic stormDemonstrated global spatial extent of storm time poloidal FLR region using observations from a constellation of widely spaced satellitesRevealed discrete spatial structures of resonant L shells with stepâlike frequency changesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137558/1/grl55775_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137558/2/grl55775.pd
Observations of a Pc5 global (cavity/waveguide) mode outside the plasmasphere by THEMIS
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95192/1/jgra21745.pd
First results from sonification and exploratory citizen science of magnetospheric ULF waves: Long-lasting decreasing-frequency poloidal field line resonances following geomagnetic storms
Magnetospheric ultra-low frequency (ULF) waves contribute to space weather in the solar wind - magnetosphere - ionosphere system. The monitoring of these waves by space- and ground-based instruments, however, produces "big data" which is difficult to navigate, mine and analyse effectively. We present sonification, the process of converting an oscillatory time-series into audible sound, and citizen science, where members of the public contribute to scientific investigations, as a means to potentially help tackle these issues. Magnetometer data in the ULF range at geostationary orbit has been sonified and released to London high schools as part of exploratory projects. While this approach reduces the overall likelihood of useful results from any particular group of citizen scientists compared to typical citizen science projects, it promotes independent learning and problem solving by all participants and can result in a small number of unexpected research outcomes. We present one such example, a case study identified by a group of students -of decreasing-frequency poloidal field line resonances over multiple days found to occur during the recovery phase of a CME-driven geomagnetic storm. Simultaneous plasma density measurements show that the decreasing frequencies were due to the refilling of the plasmasphere following the storm. The waves were likely generated by internal plasma processes. Further exploration of the audio revealed many similar events following other major storms, thus they are much more common than previously thought. We therefore highlight the potential of sonification and exploratory citizen science in addressing some of the challenges facing ULF wave research
Geotail observations of FTE velocities
We discuss the plasma velocity signatures expected in
association with flux transfer events (FTEs). Events moving faster than or
opposite the ambient media should generate bipolar inward/outward
(outward/inward) flow perturbations normal to the nominal magnetopause in
the magnetosphere (magnetosheath). Flow perturbations directly upstream and
downstream from the events should be in the direction of event motion. Flows
on the flanks should be in the direction opposite the motion of events
moving at subsonic and subAlfvénic speeds relative to the ambient
plasma. Events moving with the ambient flow should generate no flow
perturbations in the ambient plasma. Alfvén waves propagating parallel
(antiparallel) to the axial magnetic field of FTEs may generate
anticorrelated (correlated) magnetic field and flow perturbations within the
core region of FTEs. We present case studies illustrating many of these
signatures. In the examples considered, Alfvén waves propagate along
event axes away from the inferred reconnection site. A statistical study of
FTEs observed by Geotail over a 3.5-year period reveals that FTEs within the
magnetosphere invariably move faster than the ambient flow, while those in
the magnetosheath move both faster and slower than the ambient flow
THEMIS observations of compressional pulsations in the dawn-side magnetosphere: a case study
We present THEMIS-A low- and high-energy plasma, magnetic
field, and energetic particle observations of long period (11â36 min)
irregular compressional pulsations in the dawnside magnetosphere from 08:00
to 12:24 UT on 7 November 2007. We demonstrate that the pulsations maintain
thermal and magnetic pressure balance, then employ finite gyroradius
techniques to determine wave properties from the gyrophase distributions of
5â10 keV ions. The waves generally move sunward at velocities ~10 km s−1
with the background plasma convection flow. Wavelengths range from
6700 to 23 300 km, corresponding to azimuthal wavenumbers m from 18 to 76.
Wave periods decrease with increasing radial distance. Having determined the
parameters describing the waves, we consider three previously proposed
explanations: generation by substorm injection, generation by bounce or
drift-bounce instabilities, and generation by the drift-mirror instability.
The interval was quiet geomagnetically, arguing against any relationship to
substorm injections. We found that ions with low energies of 69â628 eV or
high energies of 28â615 keV would have been required to account for
drift-bounce resonance during this interval, but inspection reveals ion
fluxes at these energies near background levels during the time period
considered. On the other hand, the criteria for the drift mirror instability
are marginally satisfied. As predicted for the drift mirror instability,
particle distributions peak more sharply near 90° pitch angles during
magnetic field strength enhancements than during strength depressions. At
this point we therefore interpret the compressional pulsations observed by
THEMIS A in terms of the drift mirror instability
Concept of Multilingualism as Strategy of Language Policy and Foreign-Language Education in Europe
In this article the language policy of the European Union (EU) in the field of lobbying the concept of multilingual Europe is considered. In this research the didactic aspects of the policy of multilingualism are accented, and also the results of the approbation of policy of multilingualism in the educational theory and practice of the EU are analyzed
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