Spectrometer observations in the region near the bow shock on March 12, 1968
Directed proton fluxes measurements in bow shock, magnetosheath and solar wind by OGO 5 satellite ion spectrometer
Harris, K. K.↗
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Detection of singly ionized energetic lunar pick-up ions upstream of earth's bow shock
Singly ionized suprathermal ions upstream of the earth's bow shock have been detected by using the time-of-flight spectrometer SULEICA on the AMPTE/IRM satellite. The data were collected between August and December 1985. The flux of the ions in the mass range between 23 and 37 amu is highly anisotropic towards the earth. The ions are observed with a period of about 29 days around new moon (+/- 3 days). The correlation of the energy of the ions with the solar wind speed and the interplanetary magnetic field orientation indicates the relation to the pick-up process. We conclude that the source of these pick-up ions is the moon. We argue that due to the impinging solar wind, atoms are sputtered off the lunar surface, ionized in the sputtering process or by ensuing photoionization and picked up by the solar wind.
Hilchenbach, M.↗
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.
Korotova, Galina↗
ULF waves upstream of the Venus bow shock - Properties of one-hertz waves
Pioneer Venus Orbiter data are used here to study the properties of a class of ULF upstream waves with relatively high observed frequencies. These waves show significant similarity to 'one-Hz' waves identified at earth in the ISEE 1 and 2 observations and the whistler waves identified earlier by IMP 6 observations. The waves appear almost immediately after the spacecraft crosses the magnetic field tangent line to the bow shock surface into the region of connected field lines. The wave amplitude decreases with distance from the shock measured along the magnetic field line. Group velocities calculated using the cold plasma dispersion relation indicate that the waves have sufficient upstream velocities to propagate form the shock into the solar wind. The totality of observations seem best explained by a source of right-handed whistler mode waves at the bow shock.
Orlowski, D. S.↗
Conduction of thermal energy in the neighborhood of the earth's bow shock
The Rankine-Hugoniot equations for MHD shocks are generalized by the addition of a term to the energy conservation equation representing a nonzero heat flow in the plasma in the neighborhood of the shock. This generalization is found to be compatible with the assumption of infinite electrical conductivity. The effects of plasma waves in this treatment are of the order of the reciprocal Alfvenic Mach number squared and hence are neglected. The effect of alpha particles in the solar wind is discussed. Seven crossings of the earth's bow shock by Explorer 35 in lunar orbit are analyzed. Sufficient data are available so that the determination of a dimensionless parameter, psi, characterizing the heat-flow difference across the bow shock is possible. The values of psi indicate energy-flux densities due to heat flow which are a nonnegligible fraction of the total energy flux. Two possible interpretations of psi are discussed.
Hohlfeld, R. G.↗
Gyrating and intermediate ion distributions upstream from the earth's bow shock
Study of ISEE 2 fast plasma data reveals that many suprathermal ion events that in previous studies would have been identified as intermediate ion events are actually gyrating ion events. Of 190 apparently intermediate ion events selected on the basis of their signature in energy-time spectrograms, half are actually found to be gyrating ion events. Using a model bow shock, the shock geometries and spacecraft locations for the observed gyrating and intermediate ion events are compared and found to be quite similar. Both gyrating and intermediate ion events are found to be associated with upstream MHD-like wave activity. Most gyrating ion events are associated with large-amplitude, monochromatic, weakly compressive waves, whereas many intermediate ion events are associated with smaller-amplitude, nonmonochromatic, weakly compressive waves. Some intermediate ion events are found to have no associated waves. Detailed study of the gyrating ion distributions reveals that the distributions are typically gyrotropic within about 4 earth radii of the bow shock, whereas at larger distances (up to about 10 earth radii) upstream from the shock the distributions are frequently 'gyrophase bunched'. In light of these observational characteristics, it is concluded that gyrating ion distributions are most likely generated both through coherent wave disruption of field-aligned beams and through reflection of solar wind ions off the shock.
Fuselier, S. A.↗
Relativistic Electrons Produced by Foreshock Disturbances Observed Upstream of Earth's Bow Shock
Charged particles can be reflected and accelerated by strong (i.e., high Mach number) astrophysical collisionless shock waves, streaming away to form a foreshock region in communication with the shock. Foreshocks are primarily populated by suprathermal ions that can generate foreshock disturbances-largescale (i.e., tens to thousands of thermal ion Larmor radii), transient (approximately 5-10 per day) structures. They have recently been found to accelerate ions to energies of several keV. Although electrons in Saturn's high Mach number (M > 40) bow shock can be accelerated to relativistic energies (nearly 1000 keV), it has hitherto been thought impossible to accelerate electrons beyond a few tens of keV at Earth's low Mach number (1 ≤M <20) bow shock. Here we report observations of electrons energized by foreshock disturbances to energies up to at least approximately 300 keV. Although such energetic electrons have been previously observed, their presence has been attributed to escaping magnetospheric particles or solar events. These relativistic electrons are not associated with any solar or magnetospheric activity. Further, due to their relatively small Larmor radii (compared to magnetic gradient scale lengths) and large thermal speeds (compared to shock speeds), no known shock acceleration mechanism can energize thermal electrons up to relativistic energies. The discovery of relativistic electrons associated with foreshock structures commonly generated in astrophysical shocks could provide a new paradigm for electron injections and acceleration in collisionless plasmas.
SLAMS↗
MESSENGER Observations of Mercury's Bow Shock and Magnetopause
MESSENGER'S 14 January 2008 encounter with Mercury will provide the first new observations of the solar wind interaction with this planet since the Mariner 10 flybys that took place over 30 years ago. The closest approach distance for this first MESSENGER flyby is targeted for an altitude of 200 km as compared with the 707 km and 327 km attained by Mariner 10 on 29 March 1974 and 16 March 1975, respectively. The locations of the bow shock and magnetopause boundaries observed by MESSENGER will be examined and compared against those found in the earlier Mariner 10 measurements and the predictions of theoretical models and numerical simulations. The structure of the magnetopause will be investigated for the presence of flux transfer events or other evidence of magnetic reconnection as will the more general implications of these new MESSENGER bow shock and magnetopause observations for the global solar wind interaction with Mercury.
Slavin, James A.↗
Protons and alpha particles in field-aligned beams upstream of the bow shock
Measurements of H(+) and He(2+) ions in field-aligned beams (about 10 keV/nuc) made with the AMPTE-CCE spacecraft are reported. The proton beam population has a density of less than about 1 percent of the solar wind density and a significant thermal anisotropy, in agreement with previous observations. The observed beam velocities are in reasonable agreement with the 'direct reflection' model, in which a portion of the solar wind is reflected and energized at the earth's bow shock, but are consistently larger than expected from magnetosheath leakage models. The He(2+) ions in the beams have approximately the same velocity as the H(+) ions, but the He(2+) to H(+) density ratio is dramatically smaller than that measured simultaneously in the solar wind. The present beam observations were obtained during several of the time intervals previously analyzed by other workers, using data from the same spacecraft, who attributed the streaming upstream ions to magnetospheric rather than bow shock origin.
Ipavich, F. M.↗
Bow shock associated waves observed in the far upstream interplanetary medium.
Earth bow shock waves in far upstream interplanetary medium observed from magnetic data of Explorer 34 satellite
Fairfield, D. H.↗
Initial deceleration of solar wind positive ions in the earth's bow shock
Initial deceleration of solar wind positive ions upstream of earth bow shock determined from OGO 5 high time resolution plasma measurements
Neugebauer, M.↗
Reinterpretation of the Pioneer 6 bow shock crossing.
This paper re-examines and reinterprets the interesting bow shock crossing of Pioneer 6 on December 16, 1965, by combining the high-resolution data for the magnetic field measurements with all the available plasma data. It is shown that, although a small correction of the magnetic field data improves the validity test of the MHD Rankine-Hugoniot (R-H) conditions, it is the plasma density measurements that are the principal source of the remaining inconsistencies. With the exception of the densities, the best agreement between the measurements and the R-H relations is obtained when the specific heat ratio is slightly less than the classical value of 5/3 expected for a magnetized plasma in the magnetosheath. A more accurate shock normal determination has been made, and it is found that the shock itself is possibly in motion with respect to the earth and that locally it may be approximated as a normal shock.
Mariani, F.↗
A theory for the 2f(p) radiation upstream of the earth's bow shock
The mechanism responsible for the radiation observed near the earth bow shock at twice the plasma frequency f(p) is investigated theoretically. A model comprising two three-wave steps and involving Langmuir (L), ion-sound (S), and EM (t) waves is proposed: L + or - S yields L-prime; L + L-prime yields t. This model is shown to be consistent with observations of low-frequency S-like waves (Anderson et al., 1981), and further observational tests are suggested. A critical examination of the theory of Fung et al. (1982) is included, and it is found that an important term in the absorption coefficient was neglected. Correcting this error leads to an intrinsic theoretical brightness-temperature limit of 3 x 10 to the 9th K, well below the observed brightness temperature of the 2 f(p) radiation, about 10 to the 11th K.
Cairns, I. H.↗
Whistler wave bursts upstream of the Uranian bow shock
Observations of magnetic field wave bursts upstream of the Uranian bow shock are reported which were recorded prior to the inbound shock crossing. Three wave types are identified. One exhibits a broad spectral enhancement from a few millihertz to about 50 mHz and is seen from 17 to 10 hr prior to the inbound shock crossing. It is argued that these waves are whistler waves that have propagated upstream from the shock. A second wave type has a spacecraft frame frequency between 20 and 40 mHz, is seen only within or immediately upstream of the shock pedestal, is right-hand polarized in the spacecraft frame, and has a typical burst duration of 90 s. The third wave type has a spacecraft frame frequency of about 0.15 Hz, is seen exclusively within the shock pedestal, is left-hand polarized in the spacecraft frame, and has a burst duration lasting up to 4 min. It is argued that the low-frequency bursts are whistler waves with phase speed comparable to, but in excess of, the solar wind speed.
Smith, Charles W.↗
The earth's foreshock, bow shock, and magnetosheath
Studies directly pertaining to the earth's foreshock, bow shock, and magnetosheath are reviewed, and some comparisons are made with data on other planets. Topics considered in detail include the electron foreshock, the ion foreshock, the quasi-parallel shock, the quasi-perpendicular shock, and the magnetosheath. Information discussed spans a broad range of disciplines, from large-scale macroscopic plasma phenomena to small-scale microphysical interactions.
Onsager, T. G.↗
An empirical model of the Venusian outer environment. I - The shape of the dayside solar wind-atmosphere interface. II - The shape and location of the bow shock
Solar wind plasma and magnetic field data and ionospheric data obtained from the Pioneer Venus orbiter are discussed. The variation in the magnetic field pressure within the magnetic barrier is shown to be similar to that expected for the solar wind pressure variations along an obstacle's boundary when a more realistic approximation of the shape of the ionosphere is included. Simultaneous solar wind pressure, ionospheric pressure, and magnetic barrier pressure data reveal that the ionospheric pressure below the ionopause is approximately equal to the solar wind pressure. The magnetic barrier pressure is found to be equal to approximately 2/3 to 3/4 of both the solar wind pressure and the ionospheric pressure. Estimates of the hot plasma pressure contribution to the total pressure in the magnetic barrier vary from 1/4 to 1/3. Just below the ionopause the ionospheric pressure deviations from the mean ionospheric pressure are significant, especially below approximately 400 km; they appear to be indicative of the adjustment of the ionospheric structure to changeing solar wind conditions. A first-order model of the ionopause pressure variations as a function of height and solar-zenith angle is proposed. Venera 9 and Venera 10 bow shock crossings are then analyzed for solar zenith angles in the range from approximately 25 deg to approximately 153 deg. A comparison of Venera 9 and Venera 10 bow shock crossings with those observed by the Pioneer Venus orbiter suggests that both the secular variation and the latitudinal asymmetry may be responsible for the closer shock crossings of the Venera 9 and Venera 10 spacecraft.
Vaisberg, O. L.↗
Simulation of a perpendicular bow shock
Simulations of a high-Mach-number shock with parameters typical of the earth's bow shock are performed. The simulations rely on a hybrid code in which the ions are treated kinetically using standard particle-in-cell techniques and the electrons are treated as a massless, charge neutralizing fluid. One spatial dimension and all velocity and field components are included in the calculation. The simulations reproduce the observed ion reflection and overshoots in the magnetic field and density, features that are shown to be closely associated with ion gyration. It is noted that gyrating ions play a crucial role in building up and maintaining overshoots in the potential, density, and magnetic field.
Leroy, M. M.↗
Whistler mode wave propagation in the solar wind near the bow shock
The presence of whistler mode waves in, and upstream from, the bow shock has been well established by observation. Theoretical descriptions of the mode under solar wind conditions have been relatively meagre, however, and it may not be generally appreciated how readily whistler waves generated in the shock could occupy most of the region ahead of the shock most of the time. Graphic descriptions of phase and group velocities and group velocity directions for typical solar wind parameters are presented by using the cold plasma approximation over all appropriate frequencies and directions with respect to the IMF. The relations of whistler phase and group velocities to observations of a quasi-perpendicular shock crossing by ISEE are illustrated.
Greenstadt, E. W.↗