Engineering topics

Mozer, F. S.

Publications and source records attributed to Mozer, F. S..

At least 37 records · Page 2

NASA NTRS1995

ISEE 1 and Geotail observations of low-frequency waves at the magnetopause

Observations of waves at frequencies below approximately 200 Hz obtained near the magnetopause are presented. For one case identified in the ISEE 1 data as a period when steady state reconnection was occurring, there were waves below the lower hybrid frequency with amplitudes up to approximately 7 mV/m. Intense low-frequency waves with amplitudes up to approximately 20 mV/m at the subsolar magnetopause have also been observed by the Geotail electric field instrument. In some cases, large spiky fields were embedded in the waves. The waves observed by ISEE 1 and Geotail were large enough to provide the dissipation required for reconnection to occur.

Cattell, C.↗

NASA NTRS1994

Direct entry of dense flowing plasmas into the distant tail lobes

Electric field, magnetic field, and spacecraft potential measurements on the Geotail satellite have confirmed earlier observations of relatively dense flowing plasmas in the magnetotail lobes. Within these flowing plasmas, density discontinuities of factors of 2 to 4 were observed. At least 15 of the 18 magnetopause crossings that occurred during a 24-hour interval when the spacecraft was at GSM coordinates near X = -140 R(sub e), Y = 0, and Z = 15 R(sub e), were rotational discontinuities across which the magnetosheath plasma had direct entry into the tail lobes. Within the lobes near the rotational discontinuities, the spacecraft typically crossed a second boundary at which the plasma density decreased from its magnetosheath value by a typical factor of 1.5 to 3 while the magnetic field strength and flow speed increased. Equatorward of this density discontinuity, the plasma density and flow remained appreciable. At least 2 of the 18 magnetopause crossings may have been tangential discontinuities across which the density and magnetic field strength both changed. Within the lobes near these tangential discontinuities, significant densities of flowing plasma were observed. Since 11 of the 18 discontinuities were crossed within a time interval of less than 7 seconds, the bondary current layer was well-defined and very thin.

Mozer, F. S.↗

NASA NTRS1994

The morningside low-latitude boundary layer as determined from electric and magnetic field measurements on Geotail

On October 17, 1992, the Geotail satellite crossed the dawnside magnetopause approximately 41 times. At the majority of these crossings, the magnetic field and the normal component of the electric field were larger and the plasma density was smaller in a low-latitude boundary layer than they were in either the nearby magnetosheath or in the magnetosphere. These results are intepreted in terms of the Kelvin-Helmholtz instability associated with velocity shear at the magnetopause. Consistent with this interpretation, it is shown that the low-latitude boundary layer was the region where the flow decreased from its magnetosheath to magnetospheric value. Evidence is presented that the magnetopause was locally oriented within less than 20 deg of its nominal geometry on these crossings and that it moved with an amplitude of 1500-6000 kilometers. The thickness of the low-latitude boundary layer averaged 800 kilometers and the electric potential across it averaged 4 kilovolts with a spread of a factor of 2. Thus, the viscous interaction and similar processes are not significant contributors to magnetospheric convection.

Mozer, F. S.↗

NASA NTRS1994

Wave rectification in plasma sheaths surrounding electric field antennas

Combined measurements of Langmuir or broadband whistler wave intensity and lower-frequency electric field waveforms, all at 10-microsecond time resolution, were made on several recent sounding rockets in the auroral ionosphere. It is found that Langmuir and whistler waves are partically rectified in the plasma sheaths surrounding the payload and the spheres used as antennas. This sheath rectification occurs whenever the high frequency (HF) potential across the sheath becomes of the same order as the electron temperature or higher, for wave frequencies near or above the ion plasma frequency. This rectification can introduce false low-frequency waves into measurements of electric field spectra when strong high-frequency waves are present. Second harmonic signals are also generated, although at much lower levels. The effect occurs in many different plasma conditions, primarily producing false waves at frequencies that are low enough for the antenna coupling to the plasma to be resistive.

Boehm, M. H.↗

NASA NTRS1992

A two satellite study of nightside flux transfer events in the plasma sheet

The short-term (about 1 min) events during two consecutive substorms on March 23 1979 have been studied using high time resolution measurements of magnetic and electric fields and of the kiloelectronvolt electron flux at X about -21 R(e). Data obtained make it possible to describe the localized magnetic structures transported or propagated within the plasma sheet and to identify these events as plasma sheet nightside magnetic flux transfer events (NFTEs). The best examples of the NFTEs found so far are all observed in a thin portion of plasma sheet where the contraction of the reconnected field lines dominates over the oppositely directed pressure gradient force. Systematic differences in the magnetic variations observed at ISEE-1 and 2 indicate current concentration at the outer plasma sheet boundary during the passage of a NFTE.

Sergeev, V. A.↗

NASA NTRS1991

ISEE 1 observations of electrostatic ion cyclotron waves in association with ion beams on auroral field lines from about 2.5 to 4.5 R(E)

Quasi-monochromatic waves at about the hydrogen cyclotron frequency were observed as the ISEE 1 satellite traversed auroral field lines at radial distances of about 2.5-4.5 R(E) near midnight on June 19, 1981. Waves and both lower and higher frequencies were observed at higher altitudes, and possible electrostatic helium cyclotron and oxygen cyclotron waves occurred at lower altitudes. Upflowing hydrogen and oxygen beams and field-aligned currents occurred simultaneously. The features of the waves are most consistent with the current-driven mode. In addition, numerical studies of the linear dispersion relation, using parameters based on the observations, show that both the parallel and oblique two-stream modes and the ion-beam-driven modes were stable while oblique current-driven modes were unstable. The O(+) and H(+) distributions provide evidence for interactions with local electrostatic ion cyclotron waves and for the H(+)-O(+) two-stream instability at altitudes below the satellite.

Catell, C. A.↗

NASA NTRS1990

On the search for evidence of fast mode compressions in the near-earth tail - ISEE observations

A search for earthward propagating fast mode compressions in the near-earth tail has been conducted. ISEE electric and magnetic field data were studied for substorm and quiet times when the spacecraft was close to the neutral sheet, near midnight, and at radial distances of 5.5 to 13 R(E) (earth radii). Due to ISEE orbit characteristics, the set of events covered 12.5 hours, during which time the satellite remained between 8.5 and 13 R(E). Contrary to earlier ideas, no evidence for fast mode compression waves was found during the substorm events studied here, since plasma data and spacecraft potential data showed no density increases at the times of rapid magnetic field increases. For the one compression event for which a temporal offset between the ISEE 1 and ISEE 2 magnetic field structures could be clearly determined, the propagation velocity was about 140 km/s, well below the fast mode speed of about 400 km/s for the measured composition. During substorm events, the largest convection flows were earthward with magnitudes of 100-350 km/sec.

Moortgat, K. T.↗

NASA NTRS1990

The average tangential electric field at the noon magnetopause

Two hundred and five magnetopause passes of the ISEE 1 satellite through the magnetopause within 2 hrs of local noon during the time period 1977-1981 were examined in order to determine the relationship between the dawn-dusk tangential electric field at the magnetopause and the northward component of the magnetosheath magnetic field; the ratio of these quantities yields the speed of the plasma flow toward the magnetopause (i.e., the reconnection flow speed). The results indicate that, on the average, reconnection occurs at the subsolar magnetopause, and that the average reconnection flow speed of magnetosheath plasma toward the magnetopause is about 15 percent of the local Alfven speed.

Lindqvist, P.-A.↗

NASA NTRS1990

High-resolution sounding rocket observations of large-amplitude Alfven waves

Shear Alfven waves with amplitudes greater than 100 mV/m were observed on two recent sounding rocket flights. The largest waveforms are best described as a series of step functions, rather than as broadband noise or as single frequency waves. Complete two-dimensional E and B measurements at 4-ms time resolution were made, showing a downward propagation direction and implying insignificant reflection from the ionosphere at frequencies greater than 1 Hz. Intense, field-aligned, low-energy electron fluxes accompany the waves. Acceleration of these electrons by the Alfven waves is shown to be feasible. The waves in at least one case have a sufficently large ponderomotive potential to generate the observed density fluctuations of order one.

Boehm, M. H.↗

NASA NTRS1990

Dual sounding rocket observations of low-altitude electrostatic shocks

Two sounding rockets were used to simultaneously place two payloads on nearly the same magnetic field lines in the late-evening auroral zone. The dc electric field measurements obtained by the payloads imply a parallel potential of several kV below the higher payload, probably occurring between the two payloads. No possible resistive mechanism in observed in the 100 Hz-10 kKz band which could support the parallel field; this implies the existence of resistance-generating turbulence which are either at other frequencies, or of a type not measured by the probes, or localized parallel potentials not coincident with the payload trajectories.

Boehm, M. H.↗

NASA NTRS1987

Electric field measurements at subcritical, oblique bow shock crossings

ISEE-1 electric field measurements at three oblique, subcritical dispersive bow shock crossings are presented. The potential drops across the shock due to the large spatial scale normal component of the electric field were found to vary between 340 and 520 V. The measurements provide the first observations in a space plasma of the oscillations in the normal component of the electric field connected with the whistler precursor phase standing at a collisionless shock. Intense, rapidly varying electric fields with peak amplitudes ranging up to 100 mV/m were observed at the magnetic ramp of the shock in the high time resolution data.

Wygant, J. R.↗

NASA NTRS1987

Microphysics of the auroral acceleration region of other regions of the magnetosphere

Electric field and plasma measurements pertinent to the microphysics of the auroral acceleration region are reviewed. Observations in other regions of the magnetosphere, which appear to involve similar physical processes, are summarized in order to emphasize the requirement on Cluster instrumentation for wide dynamic range, high time resolution, time domain field, and particle measurements. It is suggested that the microphysics of current driven instabilities in the auroral acceleration region is duplicated in the high latitude boundary of the plasma sheet and that the macroscale structure of the tail is determined by this microphysics.

Mozer, F. S.↗

NASA NTRS1987

Double layers above the aurora

Two different kinds of double layers were found in association with auroral precipitation. One of these is the so-called electrostatic shock, which is oriented at an oblique angle to the magnetic field in such a way that the perpendicular electric field is much larger than the parallel electric field. This type of double layer is often found at the edges of regions of upflowing ion beams and the direction of the electric fields in the shock points toward the ion beam. The potential drop through the shock can be several kV and is comparable to the total potential needed to produce auroral acceleration. Instabilities associated with the shock may generate obliquely propagating Alfven waves, which may accelerate electrons to produce flickering auroras. The flickering aurora provides evidence that the electrostatic shock may have large temporal fluctuations. The other kind of double layer is the small-amplitude double layer found in regions of upward flowing in beams, often in association with electrostatic ion cyclotron waves. The parallel and perpendicular electric fields in these structures are comparable in magnitude. The associated potentials are a few eV. Since many such double layers are found in regions of upward flowing ion beams, the combined potential drop through a set of these double layers can be substantial.

Temerin, M.↗

NASA NTRS1987

Substorm-associated lower hybrid waves in the plasma sheet observed by ISEE 1

Observations of the electric field at frequencies from 2-128 Hz, using the burst mode of the spherical double probe on ISEE 1, have been examined for a time period previously identified as containing the traversal of a near-earth neutral line past the satellite. Intense waves (3 to over 30 mV/m) at approximately half the lower hybrid frequency were observed throughout the plasma sheet from the neutral sheet to the boundary, but only during the period of the large dc electric field and E x B velocity associated with the substorm neutral line. The wave number deduced from linear fits of the data was comparable to the inverse electron gyroradius. These results are consistent with the lower-hybrid drift instability. Although peaks between the ion and electron plasma frequency were sometimes observed simultaneously, the integrated power below 100 Hz was usually at least one to two orders of magnitude greater than that above 100 Hz. Although theoretical work has suggested that the instability would be suppressed at the neutral sheet, the largest waves observed occurred right at the neutral sheet when the southward component of the magnetic field was 6 gamma. The observed waves could provide an anomalous resistivity of about (3-1000) x 10 to the -7th S (compared to the classical value of 1 x 10 to the -18th S).

Cattell, C. A.↗

NASA NTRS1986

ISEE observations of the plasma sheet boundary, plasma sheet, and neutral sheet. I - Electric field, magnetic field, plasma, and ion composition

The first simultaneous study of dc and ac electric and magnetic fields, E x B velocity, plasma flows, ratio of plasma to magnetic field pressure, total energy density, energetic particles, and ion composition from the ISEE satellites and ground and interplanetary magnetic fields has been made to determine (1) the relationship of the previously observed electric fields at the plasma sheet boundary and at the neutral sheet to plasma parameters, and (2) whether the phenomena occurring during quiet and active times were consistent with the formation of a near-earth neutral line during substorms or with the boundary layer model. Five observations made during the study of two substorms were seen to be in agreement with the neutral-line model. The observations are consistent with the satellite being located at varying distances from the neutral line and diffusion region where reconnection and plasma acceleration were occurring. Although the z component (into or out of the ecliptic plane) of E x B convection was generally toward the neutral sheet, there were examples when it was consistent with the inferred motion of the plasma sheet past the satellite. A synthesis of previous reports on large electric fields at the plasma sheet boundary and variable fields at the neutral sheet including the associated plasma flows is also described.

Cattell, C. A.↗

NASA NTRS1986

Large plasmaspheric electric fields at L approximately 2 measured by the S3-3 satellite during strong geomagnetic activity

Large plasmaspheric electric fields at L is approximately 2 measured by the S3-3 satellite during strong geomagnetic activity are reported. Since these measurements have amplitudes comparable to those of the local corotation electric field, during such events the plasmasphere is expected to get strongly altered event at such low L-values. Furthermore, those measurements could contribute to the understanding of the physics of the convection/electric field penetration to the low latitude plasmaphere as well as the disturbed dynamo, during strong geomagnetic activity. For this purpose, critical parameters related to geomagnetic activity are also presented for the reported electric field events.

Gonzalez, W. D.↗

NASA NTRS1986

Experimental determination of the dominant wave mode in the active near-earth magnetotail

Measurements of the low frequency (2-128 Hz) electric field in the plasma sheet at approximately 19 earth radii during a substorm period obtained from the burst mode on the spherical double probe on the ISEE-1 satellite are examined. The data are analyzed to determine the frequencies and wave-lengths of the waves. It is detected that the observed frequencies correlate well with lower hybrid frequencies, the spectra have narrow peaks, and waves are present from the high latitude plasma sheet boundary to the neutral sheet. The observations are compared with theories of broad-band electrostatic waves. The data reveal that lower hybrid drift waves become unstable when the plasma sheet thins prior to substorm onset.

Cattell, C. A.↗

NASA NTRS1985

Electric fields and convection velocities associated with flux transfer events

A survey of the electric field and (E x B)/B-squared convection velocities associated with 23 flux transfer events (FTEs) in the magnetosheath and magnetosphere is presented. Twelve-second averaged electric field data show perturbations in the component of the electric field perpendicular to the magnetopause, with an average magnitude of 3.5 mV/m associated with the FTEs. Direct flux transfer events have a northward, and reverse flux transfer events a southward, E x B velocity component, in agreement with the current FTE model. The flux tubes moved across the magnetopause plane at an average E x B speed of 125 km/s with respect to the ambient E x B flow, with events located on the dawn (dusk) side tending to move downward (duskward). No large spiky electric fields of the type observed elsewhere in the magnetosphere were detected.

Dailey, R.↗