ULF waves in the foreshock

Strangeway, R. J.; Crawford, G. K.

doi:10.1016/0273-1177(94)00087-h

Cited by 93 publications

(83 citation statements)

References 37 publications

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“…There are definite enhancements in the power in the foreshock in the frequencies below 0.06 Hz and to a lesser extent at higher frequencies that are not seen in the solar wind. This is to be expected considering the prevalence of ULF waves in the foreshock (Hoppe et al, 1981;Greenstadt et al, 1995). There is, however, no evidence in these spectra for the presence of monochromatic waves unique to times when scattering is observed.…”

Section: Discussionmentioning

confidence: 80%

Direct observations of the formation of the solar wind halo from the strahl

Gurgiolo¹,

Goldstein

Viñas

et al. 2012

Ann. Geophys.

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Abstract.Observations of a continual erosion of the strahl and build up of the halo with distance from the sun suggests that, at least in part, the halo may be formed as a result of scattering of the strahl. This hypothesis is supported in this paper by observation of intense scattering of strahl electrons, which gives rise to a proto-halo electron population. This population eventually merges into, or becomes the halo. The fact that observations of intense scattering of the strahl are not common implies that the formation of the halo may not be a continuous process, but one that occurs, in part, in bursts in regions where the conditions responsible for the scattering are optimum.

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Section: Discussionmentioning

confidence: 80%

Direct observations of the formation of the solar wind halo from the strahl

Gurgiolo¹,

Goldstein

Viñas

et al. 2012

Ann. Geophys.

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“…It is well known that deep inside the quasi-parallel foreshock, two structures arise from ULF fluctuations: the shocklets and the short-large amplitude magnetic structures (SLAMS) Greenstadt et al, 1995;Scholer et al, 2003;Schwartz and Burgess, 1991;Schwartz, 1991;Schwartz et al, 1992;Giacalone et al, 1993). In the magnetic field data, the shocklets exhibit a compressive character with one steepened, shock-like edge, often accompanied by a whistler wave precursor.…”

Section: Discussionmentioning

confidence: 99%

“…The shock is labeled quasi-parallel or quasi-perpendicular, depending on whether the θ Bn is smaller or larger than 45 • . The region upstream of the quasi-parallel bow shock is populated by hot ion populations and ultra-low frequency (ULF) magnetic field fluctuations with periods of ∼ 30 s Greenstadt et al, 1995). The ULF waves can appear as sinusoidal, transverse waves propagating almost parallel with respect to the upstream IMF, or they can be compressive, obliquely propagating fluctuations.…”

Section: Introductionmentioning

confidence: 99%

“…The ULF waves can appear as sinusoidal, transverse waves propagating almost parallel with respect to the upstream IMF, or they can be compressive, obliquely propagating fluctuations. The region upstream of the Earth's bow shock that is magnetically connected to it, is called the Earth's foreshock (Le and Russell, 1992a, b;Eastwood et al, 2005;Greenstadt et al, 1995).…”

Section: Introductionmentioning

confidence: 99%

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Statistical study of foreshock cavitons

Kajdič¹,

Blanco‐Cano²,

Omidi

et al. 2013

Ann. Geophys.

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Abstract. In this work we perform a statistical analysis of 92 foreshock cavitons observed with the Cluster spacecraft 1 during the period [2001][2002][2003][2004][2005][2006]. We analyze time intervals during which the spacecraft was located in the Earth's foreshock with durations longer than 10 min. Together these amount to ∼ 50 days. The cavitons are transient structures in the Earth's foreshock. Their main signatures in the data include simultaneous depletions of the magnetic field intensity and plasma density, which are surrounded by a rim of enhanced values of these two quantities. Cavitons form due to nonlinear interaction of transverse and compressive ultra-low frequency (ULF) waves and are therefore always surrounded by intense compressive ULF fluctuations. They are carried by the solar wind towards the bow shock. This work represents the first systematic study of a large sample of foreshock cavitons. We find that cavitons appear for a wide range of solar wind and interplanetary magnetic field conditions and are therefore a common feature upstream of Earth's quasiparallel bow shock with an average occurrence rate of ∼ 2 events per day. We also discuss their observational properties in the context of other known upstream phenomena and show that the cavitons are a distinct structure in the foreshock.

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“…This region is typically populated by both highfrequency whistler waves (Fairfield 1974;Greenstadt et al 1995;Burgess 1997) and large-amplitude, low-frequency pulsations with time periods of ∼30 s and a fractional magnetic field increase B B 1  D…”

Section: Observationsmentioning

confidence: 99%

Ion Acceleration at the Quasi-Parallel Bow Shock: Decoding the Signature of Injection

Sundberg

Haynes

Burgess

et al. 2016

ApJ

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Collisionless shocks are efficient particle accelerators. At Earth, ions with energies exceeding 100 keV are seen upstream of the bow shock when the magnetic geometry is quasi-parallel, and large-scale supernova remnant shocks can accelerate ions into cosmic-rayenergies. This energization is attributed to diffusive shock acceleration;however, for this process to become active, the ions must first be sufficiently energized. How and where this initial acceleration takes place has been one of the key unresolved issues in shock acceleration theory. Using Cluster spacecraft observations, we study the signatures of ion reflection events in the turbulent transition layer upstream of the terrestrial bow shock, and with the support of a hybrid simulation of the shock, we show that these reflection signatures are characteristic of the first step in the ion injection process. These reflection events develop in particular in the region where the trailing edge of large-amplitude upstream waves intercept the local shock ramp and the upstream magnetic field changes from quasi-perpendicular to quasi-parallel. The dispersed ion velocity signature observed can be attributed to a rapid succession of ion reflections at this wave boundary. After the ions' initial interaction with the shock, they flow upstream along the quasi-parallel magnetic field. Each subsequent wavefront in the upstream region will sweep the ions back toward the shock, where they gain energy with each transition between the upstream and the shock wave frames. Within three to five gyroperiods, some ions have gained enough parallel velocity to escape upstream, thus completing the injection process.

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ULF waves in the foreshock

Cited by 93 publications

References 37 publications

Direct observations of the formation of the solar wind halo from the strahl

Direct observations of the formation of the solar wind halo from the strahl

Statistical study of foreshock cavitons

Ion Acceleration at the Quasi-Parallel Bow Shock: Decoding the Signature of Injection

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