Engineering topics

Russell, C. T.

Publications and source records attributed to Russell, C. T..

At least 163 records · Page 9

NASA NTRS1995

Observations of Ionospheric Escape on Venus' Nightside

A population of low-energy (0-250 V E/q) ions with tailward directed velocity vectors and energies above that for escape from Venus is evident in nightside data from the Ames plasma analyzer on the Pioneer Venus Orbiter spacecraft. Good correlations with solar wind parameters were not obtained for the magnitudes of these ion fluxes, but tendencies for occurrence at times of tailward oriented magnetic fields and for alignment of the ion flows with the magnetic field were found. These tendencies seemed to be enhanced for higher-energy ions. In a few cases where comparisons were made, the ion fluxes were consistent with simultaneous O(+) measurements by the neutral mass spectrometer experiment on the spacecraft. The mean flux observed of the escaping nightside ions, averaged over an approximately 10-week-long spacecraft nightside season, was less than 2 x 10(exp 6)/sq cm/s.

Mihalov, J. D.↗

NASA NTRS1995

Observations of Ionospheric Escape on Venus' Nightside

Mihalov, J. D.↗

NASA NTRS1995

Studies of the draping and flaring angles of the Mars and Earth magnetotails

Observations of the Mars tail by the spacecraft have been used to estimate the draping angle of the magnetic field within the tail and the boundary flaring angle. The boundary of the tail is defined by the sudden disappearance of the proton flux by the TAUS ion spectrometer. Solar wind measurements by the TAUS instrument are used to calculate the approximate solar wind dynamic pressure when the spacecraft is within the tail boundary. The average draping angle (Acrsin((square root of (B(sub y)(exp 2) + B(sub z)(exp 2)))/B(sub T))) is found to be 27.2 deg +/- 1.4 deg. The draping angle magnitude depends on the solar wind dynamic pressure, but is quite variable. The flaring angle of the tail boundary at X = -2.5 R(sub M) has also been calculated from the balance of pressure between the lobe of the Martian tail and the component pressures of the solar wind. The flaring angle depends strongly on the solar wind dynamic pressure, and this dependence is identical to that obtained at the Earth by Petrinec and Russell. However, the magnitude of the flaring angle at Mars X = -2.5 R(sub M) is one-half the value obtained at Earth for -22.5 R(sub E) is less than or equal to X -10 R(sub E).

Zhang, T.-L.↗

NASA NTRS1995

Ion populations in the tail of Venus

Plasma measurements in the tails of Venus showed the existence of several ion populations. Measurements performed on Venera and Pioneer Venus spacecraft at different planetocentric distances showed the evolution of the plasma parameters along the tail. Low-energy ion fluxes measured in the tail at close downstream distances, are also observed farther downstream, and show low acceleration from 0.5 R(sub V) to 12 R(sub V). High energy ions (energetic O(+) ions) reported from Pioneer Venus Orbiter (PVO) observations in the tail at 10-12 R(sub V) seem to be the same ion component that was observed as energetic ions at the tail boundary close to the planet on Venera spacecraft. We give evidence that these ions are accelerated in the narrow shear layer near the tail boundary.

Vaisberg, O.↗

NASA NTRS1995

Comparison of properties of upstream whistlers at different planets

Whistler mode waves have been recorded in the upstream region of Mercury, Venus, Earth and Saturn. They are elliptically polarized and observed typically at frequencies between 0.1 to 4 Hz. These intrinsically right handed waves can be left-handed polarized in the spaceframe as a result of strong negative Doppler shift. The waves propagate at an angle between 10 and 60 deg to the background magnetic field, with (Delta B)/B rarely exceeding 0.1. Comprehensive studies of these waves at Earth and Venus indicate that upstream whistlers are generated at the shock rather than locally in the foreshock. In this paper, we compare properties of upstream whistlers at all these planets. We also discuss the utilization of selected properties of these waves to evaluate the effective Alfvenic Mach number and the shock thickness at Mercury where solar wind measurements are not available.

Orlowski, D. S.↗

NASA NTRS1995

Properties of ultra low frequency upstream waves at Venus and Saturn: A comparison

The upstream regions of all planets, except Pluto, have been investigated, using in situ spacecraft measurements and a variety of analysis techniques. The detailed studies at Earth indicate that these waves are generated locally in the magnetically connected solar wind by the interaction with ions backstreaming from the shock. However, since the properties of the solar wind vary with heliocentric distance and since properties of planetary shocks depend on plasma beta, interplanetary magnetic field (IMF) spiral angle and Mach number, the amount of heating, acceleration efficiencies, etc. significantly change with heliocentric distance. In turn the waves seen at each planet propagate not in the same but different (physical) propagation modes. In this paper we compare the ULF wave observations at an outer and an inner planet. We use the results of the ratio, quantites easily derivable with sufficient accuracy at each planet. We use the full electromagnetic dispersion relation for comparison with theoretical predictions.

Orlowski, D. S.↗

NASA NTRS1995

A study of flux transfer events at different planets

Flux transfer events (FTEs) are disturbances in and near the magnetopause current layer that cause a characteristic signature in the component of the magnetic field parallel to the average boundary normal. These disturbances have been observed at Mercury, Earth and Jupiter but not at Saturn, Uranus or Neptune. At Earth, FTEs last about 1 minute and repeat about every 8 but at Mercury, a much smaller magnetosphere, the events last seconds and are tens of seconds apart. These features have been interpreted in terms of magnetospheric flux ropes connected to the interplanetary magnetic field, arising as the result of reconnection. An analogous phenomenon occurs at Venus where magnetic flux ropes arise at the ionosphere, a boundary between a very strongly magnetized one. However, here the flux ropes do not appear to be due to reconnection.

Russell, C. T.↗

NASA NTRS1995

The solar wind interaction with Venus: A comparison of Galileo and Pioneer Venus observations

The rudimentary measurements of the instruments on Pioneer Venus over a 14-year span have provided a strong framework for the interpretation of the observations with a more sophisticated instrument package during the Galileo Venus flyby in February 1990. In some cases the Galileo results provided independent confirmation of earlier inferences. In other cases completely new data were obtained. Nevertheless, because of limitations of the instruments and the trajectory and thermal restraints some outstanding questions were not addressed. Much has been learned but there is still much more to do.

Russell, C. T.↗

NASA NTRS1995

Venus planetary lightning rate as deduced from VLF bursts

Statistical studies of the VLF bursts detected in the nightside ionosphere of Venus show that the bursts fall into two classes. The first consists of signals detected when vertical propagation within the whistler-mode resonance cone is allowed. The second consists of signals whose burst rate decreases rapidly as a function of increasing altitude, with a scale height of about 20 km. These non-whistler-mode signals also display a strong dependence on local time, with the burst rates being largest in the post-dusk local time sector. Since these signals are not propagating we assume that they correspond to a 'near-field' or prompt response to a lightning stroke. As such we can use these signals to estimate the planetary lightning rate, and we find that the rate at Venus is comparable to or greater than the terrestrial planetary rate of 100 flashes/sec.

Ho, C.-M.↗

NASA NTRS1995

A simple test of the induced nature of the Martian tail

The cross flow direction of the interplanetary magnetic field is strongly correlated with the cross flow direction several hours earlier and later. This correlation allows a simple test of the nature of the magnetic field in the Martian magnetotail. If the magnetotail is entirely induced, then the cross tail direction of the magnetic field should be along the direction of the cross flow component just upstream of the bow shock. We find that these directions of the tail field and the implementary magnetic field are so highly correlated that any intrinsic magnetic field of Mars must make at most a small contribution to the magnetotail. We estimate an upper limit to the magnetic moment of Mars to be about 4 x 10(exp 11) T(cu m).

Russell, C. T.↗

NASA NTRS1995

Solar cycle variation of interplanetary shocks, coronal mass ejections, and stream interactions observed at 0.7 AU

A survey of the Pioneer Venus Orbiter (PVO) magnetometer and plasma data from 1979-1980, shows that the occurrence frequency of interplanetary shocks, coronal mass ejections (CMEs) and stream interactions observed at 0.7 AU exhibits a solar cycle variation. As previously found at 1 AU, the observed number of both interplanetary shocks and CMEs peaks during solar maximum (approximately 16 and approximately 27 per year, respectively) and reaches a low during solar minimum (approximately 0 and approximately 7 per year, respectively), in phase with the variation in smoothed sunspot number. The number of stream interactions observed varies in the opposite manner, having a minimum during solar maximum (approximately 15 per year) and a maximum during solar minimum (approximately 34 per year). The percentage of CMEs and stream interactions producing interplanetary shocks also varies during the solar-cycle and exhibits interesting behavior during the declining phase. While the number of CMEs observed during this phase is decreasing, the percentage of CMEs producing interplanetary shocks reaches a maximum. Also, while the number of stream interactions observed is increasing, but has not reached maximum during the declining phase, the percentage of stream interactions producing interplanety shocks is at a maximum.

Lindsay, G. M.↗

NASA NTRS1995

Propagation and damping of broadband upstream whistlers

Previous studies indicated that damping rates of upstream whistlers strongly depend on the details of the electron distribution function. Moreover, detailed analysis of Doppler-shift and whistler dispersion relation indicated that upstream whistlers propagate obliquely in a broad band. In this paper we present results of a kinetic calculation of damping lengths of wide-band whistlers using the sum of 7-drifting bi-Maxwellian electron distributions as a best fit to the International Sun Earth Explorer (ISEE) 1 electron data. For 2 cases, when upstream whistlers are observed, convective damping lengths derived from ISEE magnetic field and ephemeris data are compared with theoretical results. We find that the calculated convective damping lengths are consistent with the data and that upstream whistlers remain marginally stable. We also show that the slope of plasma frame spectra of upstream whistlers, obtained by direct fitting of the observed spectra is between 5 and 7 with a sharp lower frequency cutoff corresponding to a wavelength of about one ion inertial length. When the solar wind velocity is directed largely along the wave normal of the upstream whistlers the polariztion of the right hand waves becomes reversed and low frequencies are switched to high resulting in a peaked spectrum with a strong high frequency cutoff. The overall spectral, wave and particle characteristics, proximity to the shock as well as propagation and damping properties indicate that these waves cannot be generated locally. Instead the observed upstream whistlers arise in the shock ramp most likely by a variety of cross-field drift and/or anisotropy driven instabilities.

Orlowski, D. S.↗

NASA NTRS1995

Experimental studies of the properties of 'simulated' upstream turbulence using a statistical multipoint method

In this report we present a different approach to the multipoint measurement of magnetic fields and plasma. This is called the multi-spacecraft ensemble technique (MET), essentially free of process restrictions, such as linearity and stationarity. We comprehensively discuss the other conditions and limitations intrinsic to this statistical method. We also show the results of the application of the ensemble method to the synthetic data obtained from a hybrid simulation in the region upstream of a quasi-parallel shock. The important implications of the above approach for the CLUSTER mission are discussed.

Orlowski, D. S.↗

NASA NTRS1995

A study of the solar wind deceleration in the Earth's foreshock region

Previous observations have shown that the solar wind is decelerated and deflected in the earth's upstream region populated by long-period waves. This deceleration is corelated with the 'diffuse' but not with the 'reflected' ion population. The speed of the solar wind may decrease tens of km/s in the foreshock region. The solar wind dynamic pressure exerted on the magnetopause may vary due to the fluctuation of the solar wind speed and density in the foreshock region. In this study, we examine this solar wind deceleration and determine how the solar wind deceleration varies in the foreshock region.

Zhang, T.-L.↗

NASA NTRS1995

Ultra low frequency waves at the Earth's bow shock

The Earth's bow shock is a bountiful generator of waves. Some of these waves have group velocities that exceed the solar wind velocity directed into the shock and can propagate upstream against the flow. Upstream whistlers observed close to one Hertz in the spacecraft frame have been seen many Earth radii upstream. A second whistler mode wave, called the precursor, propagates upstream along the shock normal but is phase standing in the solar wind flow. The damping of both whistler mode waves is consistent with Landau damping. At low Mach numbers the precursor is connected to the non-coplanarity component in the shock ramp. At higher Mach numbers the upstream waves cannot propagate upstream and ion reflection becomes more important in providing free energy for wave particle interactions. The non-coplanarity component is still present but it now initiates a downstream wave train. Generally the waves just downstream from the bow shock are left hand circularly polarized ion cyclotron waves propagating along the magnetic field at the Alfven velocity. When the upstream Mach number is high and the helium content of the plasma is high, mirror mode waves are observed.

Russell, C. T.↗

NASA NTRS1995

Observation of a slow-mode shock in the dayside magnetopause reconnection layer

Plasma and magnetic field data from the International Sun Earth Explorer (ISEE) 2 spacecraft recorded on 29 Oct 1979 provide evidence for a slow shock (SS) in the reconnection layer of the dayside magnetopause. This layer is bounded on the magnetosheath side by the SS and on the magnetospheric side by a rotational discontinuity (RD). The direction of the accelerated plasma flow, the earthward sense of the normal magnetic field across both discontinuities, and the relative orientation of the SS and the RD all indicate that the reconnection site was located south of the spacecraft. Examination of the substantial pressure anisotropy downstream of the SS explains two unusual properties of the shock: (1) the slow-mode and intermediate-mode phase speeds are inverted downstream of the SS such that the RD propagates behind the SS rather than ahead of it; (2) the magnetic wave polarization reserves such that the SS initially displays a left-handed polarization and then switches to a right-handed polarization inside the shock structure.

Walthour, D. W.↗

NASA NTRS1995

Data management, archiving, visualization and analysis of space physics data

A series of programs for the visualization and analysis of space physics data has been developed at UCLA. In the course of those developments, a number of lessons have been learned regarding data management and data archiving, as well as data analysis. The issues now facing those wishing to develop such software, as well as the lessons learned, are reviewed. Modern media have eased many of the earlier problems of the physical volume required to store data, the speed of access, and the permanence of the records. However, the ultimate longevity of these media is still a question of debate. Finally, while software development has become easier, cost is still a limiting factor in developing visualization and analysis software.

Russell, C. T.↗

NASA NTRS1995

Educational software for the visualization of space plasma processes

The UCLA Space Physics Group has developed educational software composed of a series of modules to assist students with understanding basic concepts of space plasmas and charged particle motion. Present modules cover planetary magnetospheres, charged particle motion, cold plasma waves, collisionless shock waves, and solar wind. The software is designed around the principle that students can learn more by doing rather than by reading or listening. The programs provide a laboratory-like environment in which the student can control, observe, and measure complex behavior. The interactive graphics environment allows the student to visualize the results of his or her experimentation and to try different parameters as desired. The current version of the software runs on UNIX-based operating systems in an X-Windows environment. It has been used in a classroom setting at both UCLA and the University of California at San Diego.

Russell, C. T.↗