Spectral analysis of magnetohydrodynamic fluctuations near interplanetary shocks (original) (raw)
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ARTEMIS Observations of Plasma Waves in Laminar and Perturbed Interplanetary Shocks
The Astrophysical Journal, 2021
The “Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun” mission provides a unique opportunity to study the structure of interplanetary shocks and the associated generation of plasma waves with frequencies between ∼50 and 8000 Hz due to its long duration electric and magnetic field burst waveform captures. We compare wave properties and occurrence rates at 11 quasi-perpendicular interplanetary shocks with burst data within 10 minutes (∼3200 proton gyroradii upstream, ∼1900 downstream) of the shock ramp. A perturbed shock is defined as possessing a large amplitude whistler precursor in the quasi-static magnetic field with an amplitude greater than 1/3 the difference between the upstream and downstream average magnetic field magnitudes; laminar shocks lack these large precursors and have a smooth, step function-like transition. In addition to wave modes previously observed, including ion acoustic, whistler, and electrostatic solitary ...
Geophysical Research Letters, 1992
In examining the March 23-25, 1991 Ulysses (2.2 AU) described in Zwickl et al. (1983) and Tsurutani et al. (1988). It is high speed solar wind events, we find two distinct plasma wave quite interesting to note that the second shock (S2) is propagating modes' steepened magnetosonic waves with whistler precursors into the driver gas of the previous event. To our knowledge, this is and mirror mode structures. These two modes are locally generated the first event of this type to be reported in the literature. by plasma instabilities, presumably associated with anisotropies This Figure shows the location of samplings of wave events existing in the energetic shock particles and solar wind plasma, relative to the complex stream structures. W I occurs just upstream respectively. The magnetosonic waves are generated by a fight-of the S1 shock. W2 occurs in the downstream sheath location. The hand resonant instability associated with a ~ 40 keV ion beam. W3 event is located in a low field region just ahead of the driver gas. By an extrapolation of the results presented here, assuming This is a high plasma beta region. The actual values will be microtimes and nanoflares at the Sun generate shocks in the lower discussed later. The W4 and W5 regions are upstream of the S2 corona and these shocks accelerate energetic ions, we suggest that shock. The S2 shock normal angle is 60 ø (Burton eta!., this issue). the ions, via the right-hand resonant instability, generate Presumably, the energetic particles generating the waves are magnetosonic waves which steepened to form "microshocks" (such propagating from the shock into this upstream region. The latter is a as shown here). These shocks could, in turn, accelerate more very unusual region in that the energetic particle pressure exceeds energetic ions, !ead/ng to a shock/energetic ion/magnetosonic wave the solar wind pressure by a factor of 50 to 300 (Goldstein et al., cascade. These newly formed magnetosonic waves and shocks this issue). Discussion of the specific wave properties and wave presumably could propagate in a broad range of directions, leading generation mechanisms will follow. to energy dissipation over a large region of the outer corona. The power spectra for the transverse components, the fieldaligned component and field magnitude were calculated for the The calculated resonant parallel energies is-• 40 keV. Similar Parker, E. N., Nanoflares and the Solar X-Ray Corona, Astrophys. calculations for the wave interval W5 give comparable to slightly J., 330, 474, 1988. lower energies. These values are comparable to that of the bulk of Parker, E. N., Intrinsic Magnetic Discontinuities and Solar X-Ray the high energy ions (Lanzerotti et al., this issue).
Magnetohydrodynamic Fast Shocks and Their Relation to Solar Energetic Particle Event Intensities
Terrestrial, Atmospheric and Oceanic Sciences, 2013
Gradual solar energetic particles (SEPs) are associated with interplanetary (IP) shock driven by coronal mass ejections. Testing theories/models that are built around shock acceleration mechanisms is difficult due to the complexity of SEP fluxes acquired by single-point measurements. To circumvent this, we correlate fast-forward shock Mach numbers derived from a 1.5D magnetohydrodynamics simulation with the intensity of solar energetic oxygen (O) and helium-4 (4 He) particles acquired by instruments aboard the ACE spacecraft during a series of coronal mass ejections in 2003 (October 28-31). A good correlation at the 5% significance level is found for O and 4 He with energy (E) > ~10 MeV n-1 , with the peak correlation coefficient r = 0.82 for O (E = 63.8-89.8 MeV n-1) and r = 0.77 for 4 He (E = 18.0-29.4 MeV n-1), respectively, for hourly averaged data. This result not only bolsters the causal relationship between IP fast shocks and SEPs, but also suggests that the Mach number of IP shocks is one of the major controlling parameters for the intensity of SEPs measured in the near-Earth space.
Large amplitude MHD waves upstream of the Jovian bow shock
Journal of Geophysical Research, 1983
Observations of large amplitude MHD waves upstream of Jupiter l a bow shock are analyzed. The waves are found to be right circularly polarized in the solar wind frame which suggests that they are propagating in the fast magnetosonic mode. A complete spectral and minimum variance eigenvalue analysis of the data was performed. The power spectrum of the magnetic fluctuations contains several peaks. The fluctuations at 2.3 mHz have a direction of minimum variance along the direction of the average magnetic field. Several harmonics at 6, 9, and 12 mHz are also present. The direction of minimum variance of
… of the 17th Annual …, 2008
Numerically, we studied the propagation properties of the fast MHD waves in the Earth magnetosphere caused by the fast interplanetary shock interaction with the magnetopause. The study of the temporal and spatial wave front peculiarities is based on the Huygens-Fresnel principle. A multispacecraft analysis of the propagation properties is performed to confirm the results of the numerical simulation. Obtained numerical results were found to be in a good agreement with the spacecraft observations.
We present in situ observations of a shock-induced substorm-like event on 13 April 2013 observed by the newly launched Van Allen twin probes. Substorm-like electron injections with energy of 30–500 keV were observed in the region from L ∼5.2 to 5.5 immediately after the shock arrival (followed by energetic electron drift echoes). Meanwhile, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 150 s emerged following the magnetotail magnetic field reconfiguration after the interplanetary (IP) shock passage. The poloidal mode is more intense than the toroidal mode. The 90◦ phase shift between the poloidal mode Br and Ea suggests the standing poloidal waves in the Northern Hemisphere. Furthermore, the energetic electron flux modulations indicate that the azimuthal wave number is ∼14. Direct evidence of drift resonance between the injected electrons and the excited poloidal ULF wave has been obtained. The resonant energy is estimated to be between 150 keV and 230 keV. Two possible scenaria on ULF wave triggering are discussed: vortex-like flow structure-driven field line resonance and ULF wave growth through drift resonance. It is found that the IP shock may trigger intense ULF wave and energetic electron behavior at L ∼3 to 6 on the nightside, while the time profile of the wave is different from dayside cases.
Journal of Geophysical Research, 1999
Several events have been identified of an ion foreshock extending up to 250 RE upstream of the Earth. These events occur mostly during periods of slowly drifting radial interplanetary magnetic field (IMF) when the 1-min average values of the strengths of the IMF and the solar wind (SW) speeds are mostly steady. For their analysis an analytical solution to the problem of the closest approach of an IMF line to two spacecraft is given. We used this method to find intervals of magnetic conjunction between the bow shock and the upstream regions at GEOTAIL and Wind. This solution is obtained by determining the minimum angle 0 (as a function of time) between the mean direction of the IMF (measured at Wind) and the vectordifference (rwI-r) of the locations of Wind and the point (attached on the field line) which went earlier by GEOTAIL. Here we take into account the mean drift of the flux lines with the SW, by assuming that the spacecraft were located in the same heliospheric magnetic domain. We have tested this method against a set of selected cases which show a steady presence of the ion foreshock close to the bow shock (GEOTAIL) and its sporadic presence far upstream (Wind). We have found our method to be accurate within a few Earth radii (RE). We have identified an outstanding candidate for the bow shock, GEOTAIL, and Wind sequential magnetic conjunction, which occurred on June 11, 1995. Additionally, this diagnostic technique has been applied to nine more intervals of simultaneous occurrences of intensity enhancements of broadband ultralow-frequency (ULF) waves, and fluctuating fluxes of scattered energetic ions (40-140 keV). Very broad ion foreshock regions (> 40 RE) are commonly observed during the subset of events characterized by a high-speed SW. The observed frequencies of the ULF waves are basically enhanced transversal modes in the range from-1/10 to 2/3 of proton cyclotron frequency, f. Fluctuations in the energetic ion fluxes were also observed in this frequency range for all the cp cases. Therefore we argue that the nature of the coupling between ULF waves and energetic ions is similar both in the near as well as far upstream regions of the Earth's bow shock.
Nonlinear Processes in Geophysics, 2005
Alfvén waves, discontinuities, proton perpendicular acceleration and magnetic decreases (MDs) in interplanetary space are shown to be interrelated. Discontinuities are the phase-steepened edges of Alfvén waves. Magnetic decreases are caused by a diamagnetic effect from perpendicularly accelerated (to the magnetic field) protons. The ion acceleration is associated with the dissipation of phasesteepened Alfvén waves, presumably through the Ponderomotive Force. Proton perpendicular heating, through instabilities, lead to the generation of both proton cyclotron waves and mirror mode structures. Electromagnetic and electrostatic electron waves are detected as well. The Alfvén waves are thus found to be both dispersive and dissipative, conditions indicting that they may be intermediate shocks. The resultant "turbulence" created by the Alfvén wave dissipation is quite complex. There are both propagating (waves) and nonpropagating (mirror mode structures and MDs) byproducts. Arguments are presented to indicate that similar processes associated with Alfvén waves are occurring in the magnetosphere. In the magnetosphere, the "turbulence" is even further complicated by the damping of obliquely propagating proton cyclotron waves and the formation of electron holes, a form of solitary waves. Interplanetary Alfvén waves are shown to rapidly phase-steepen at a distance of 1 AU from the Sun. A steepening rate of ∼35 times per wavelength is indicated by Cluster-ACE measurements. Interplanetary (reverse) shock compression of Alfvén waves is noted to cause the rapid formation of MDs on the sunward Correspondence to: B. T. Tsurutani (bruce.tsurutani@jpl.nasa.gov) side of corotating interaction regions (CIRs). Although much has been learned about the Alfvén wave phase-steepening processfrom space plasma observations, many facets are still not understood. Several of these topics are discussed for the interested researcher. Computer simulations and theoretical developments will be particularly useful in making further progress in this exciting new area.
Electromagnetic waves and electron anisotropies downstream of supercritical interplanetary shocks
Journal of Geophysical Research: Space Physics, 2013
We present waveform observations of electromagnetic lower hybrid and whistler waves with f ci f < f ce downstream of four supercritical interplanetary (IP) shocks using the Wind search coil magnetometer. The whistler waves were observed to have a weak positive correlation between δ B and normalized heat flux magnitude and an inverse correlation with T eh /T ec. All were observed simultaneous with electron distributions satisfying the whistler heat flux instability threshold and most with T ⊥h /T h > 1.01. Thus, the whistler mode waves appear to be driven by a heat flux instability and cause perpendicular heating of the halo electrons. The lower hybrid waves show a much weaker correlation between δ B and normalized heat flux magnitude and are often observed near magnetic field gradients. A third type of event shows fluctuations consistent with a mixture of both lower hybrid and whistler mode waves. These results suggest that whistler waves may indeed be regulating the electron heat flux and the halo temperature anisotropy, which is important for theories and simulations of electron distribution evolution from the sun to the earth.
Energetic protons associated with a forward-reverse interplanetary shock pair at 1 A.U
Planetary and Space Science, 1977
A forward-reverse interplanetary shock was observed on 25 March 1969 by the magnetometer and ulasma detector on the HEOS-1 satellite. This relatively rare event was described by Chao et al. (1472) who concluded that the shock pair was formed at a distance 0.10-0.13A.U. upstream of the Earth as a result of the interaction between a fast and a slow solar wind streams. Simultaneous observations of 1 MeV solar proton fluxes were also performed on HEOS-1. A characteristic intensity peak was observed as the forward shock passed by the spacecraft. The evolution of the proton intensity, together with a detailed analysis of anisotropies and pitch angle distributions show a complex dynamic picture of the effect of the forward shock on the ambient proton population. Significant changes in particle fluxes are seen to be correlated with fluctuations in the magnetic field. It is suggested that simple geometrical models of shock-associated acceleration should be expanded to include the effect of magnetic fluctuations on particle fluxes. The interaction region limited by the forward and reverse shocks contained a large variety of magnetic fluctuations. Following the tangential discontinuity separating the fast solar wind stream from the preceding slow stream, a sunward flow was observed in the proton data, followed by a small but significant drop in intensity _ prior to the reverse shock.