A comparison of ULF fluctuations in the solar wind, magnetosheath, and dayside magnetosphere: 1. Magnetosheath morphology

Engebretson, M. J.; Lin, N.; Baumjohann, W.; Luehr, H.; Anderson, B. J.; Zanetti, L. J.; Potemra, T. A.; McPherron, R. L.; Kivelson, M. G.

doi:10.1029/90ja02101

Cited by 95 publications

(60 citation statements)

References 47 publications

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“…the power of these waves in the magnetosphere should also depend on the solar wind speed.738 B. Heilig et al: Upstream waves observed in the topside ionosphere by CHAMP through the magnetosheath (Russell et al, 1983), enter the magnetosphere near the subsolar point of the magnetopause (Engebretson et al, 1991b;Krauss-Varban, 1994), propagate across the magnetosphere, enter the ionosphere and reach the ground as geomagnetic pulsations (Yumoto et al, 1984).…”

Section: Introductionmentioning

confidence: 99%

Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground

2007

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Abstract. Based on magnetic field measurements from the satellite CHAMP, a detailed picture could be obtained of the upstream wave (UW) distribution in the topside ionosphere. The low, near-polar orbit of CHAMP, covering all local times, allows the global distribution of this type of pulsation to be revealed. The observations from space are compared to recordings of the ground-based MM100 meridional array covering the latitude range 66 • to 42 • in magnetic coordinates. UWs show up very clearly in the compressional component of the satellite magnetic field data, whereas on the ground, their signature is found in the H component, but it is mixed with oscillations from field line resonant pulsations. Here we first introduce a procedure for an automated detection of UW signatures, both in ground and space data. Then a statistical analysis is presented of UW pulsations recorded during a 132-day period, centred on the autumn 2001 equinox. Observations in the top-side ionosphere reveal a clear latitudinal distribution of the amplitudes. Largest signals are observed at the equator. Minima show up at about 40 • latitude. The coherence between ground and satellite wave signatures is high over wide latitude and longitude ranges. We make suggestions about the entry mechanism of UWs from the foreshock region into the magnetosphere. The clear UW signature in satellite recordings between −60 • and 60 • latitude allows for detailed investigations of the dependence on solar wind conditions. We test the control of solar wind speed, interplanetary magnetic field strength and cone angle on UWs. For the first time, it is possible to derive details of the Doppler-shift effect by modifying the UW frequency from direct observations. The results reconcile foreshock wave generation predictions with near-Earth observations.

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Section: Introductionmentioning

confidence: 99%

Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground

2007

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“…Engebretson et al [1994] later showed quantitatively that observed modulations of precipitating energetic electrons near the cusp were sufficient to generate the Pc3-4 pulsations simultaneously observed nearby on the ground. The mechanism(s) responsible for precipitating these energetic electrons are themselves poorly understood, although observational studies by Engebretson et al [1991b] and Linet al [1991a, b] suggested that large, highly localized variations in the dynamic pressure in the magnetosheath, generated by these upstream waves, may compress and distort regions near the dayside magnetopause and thus cause such precipitation. Their observations also indicated large bipolar excursions of the Bz component of the magnetosheath magnetic field on similar timescales which, interestingly enough, appeared to have little dependence on the sign of the (relatively small) IMF Bz component.…”

Section: Introductionmentioning

confidence: 99%

A conjugate study of Pc3–4 pulsations at cusp latitudes: Is there a clock angle effect?

Engebretson¹,

Cobian²,

Posch³

et al. 2000

J. Geophys. Res.

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We further find little seasonal dependence in the ratio of power in the two cusp regions other than that attributable to differences in solar illumination. These observations, in conjunction with the well-known sharp cutoff in wave activity for cone angles above 45 ø , indicate that only those perturbations occurring at the subsolar bow shock can reach the magnetopause and propagate to any location in the dayside magnetosphere. In addition, the absence of a clock angle effect supports earlier suggestions that Pc3-4 signals in the magnetosheath do not cross streamlines and thus do not propagate as waves, but are rather convected as spatial structures in the highly turbulent, high-beta downstream magnetosheath plasma.

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“…Not only transient perturbations at the magnetopause [Fairfield et al, 1990;Sibeck et al, 2003] and ULF pulsations in the magnetosphere Engebretson et al, 1991] are linked to the waves in the foreshock, but bow shock accelerated particles at times also appear in the magnetosphere [Fuselier et al, 2002]. An important region of such plasma penetrations is the magnetospheric cusp in which magnetic field lines are open to the magnetosheath allowing direct entry of the solar wind particles [Haerendel et al, 1978].…”

Section: Introductionmentioning

confidence: 99%

Connection between bow shock and cusp energetic ions

Lin

Wang

Chang

2007

Geophysical Research Letters

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[1] A linkage between energetic ions in the bow shock and the cusp is established using a three-dimensional (3-D) selfconsistent global hybrid simulation, for a case of the interplanetary magnetic field (IMF) condition favoring high-latitude magnetic reconnection and inter-connection between field lines in the quasi-parallel bow shock and the cusp. A diffuse ion distribution is obtained in the quasiparallel shock and foreshock region, where large-amplitude waves and turbulence are present. Its energy spectrum is well described by an exponential function as in the case for upstream diffuse ions previously observed. These bow shock accelerated ions, upon being transmitted into the cusp region, form the bulk of cusp energetic ions. By tracing particles from the solar wind to the cusp, it is found that the source of acceleration for the cusp energetic ions is predominantly in the quasi-parallel shock and foreshock region, through a Fermi-type acceleration mechanism. Contribution to the cusp energetic ions from magnetosheath/ cusp waves and magnetic reconnection appears relatively minor. Owing to the limitation of the model used, the magnetospheric source for energetic particles in the cusp cannot be fully investigated.

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A comparison of ULF fluctuations in the solar wind, magnetosheath, and dayside magnetosphere: 1. Magnetosheath morphology

Cited by 95 publications

References 47 publications

Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground

Comprehensive study of ULF upstream waves observed in the topside ionosphere by CHAMP and on the ground

A conjugate study of Pc3–4 pulsations at cusp latitudes: Is there a clock angle effect?

Connection between bow shock and cusp energetic ions

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