C. Russell - Academia.edu (original) (raw)

Papers by C. Russell

Eos, Transactions American Geophysical Union, 1994

An important use of ground magnetometer observations in the 21st century is magnetoseismic resear... more An important use of ground magnetometer observations in the 21st century is magnetoseismic research, which can be performed through two different methodologies. Normal-mode magnetoseismology uses the field line resonance (FLR) frequencies to calculate the plasma density in the magnetosphere. Travel-time magnetoseismology estimates the start time and location of impulsive events in the magnetosphere, such as sudden impulses and substorm onsets, by timing the arrival of impulse signals, and through the process the density structure of the magnetosphere can also be inferred. An existing magnetometer project for magnetoseismic research is the nine-station Mid-continent Magnetoseismic Chain (McMAC) that provides observations along 330&deg magnetic longitude in the U.S. and Mexico. The more recent Falcon magnetometer project further augments the FLR observations in the U.S. by setting up new stations spanning from Alaska to Maryland. Aided by the recent finding that FLR signatures can usu...

Eos, Transactions American Geophysical Union, 1985

The term “solar-terrestrial relations” (or “solar-terrestrial physics”) has, in recent years, ass... more The term “solar-terrestrial relations” (or “solar-terrestrial physics”) has, in recent years, assumed a wide range of meanings. In its broadest interpretation it encompasses the full gamut of space plasma physics (or solar system space physics); in particular, it encompasses the interaction of solar system plasmas with all the planets and their atmospheres, not just the earth and its atmosphere. In its narrowest interpretation it refers to the series of links through which solar activity influences the earth's magnetosphere, upper atmosphere, and troposphere. The term “space plasma physics” refers explicitly to the former, broader topic, i.e., the physics of solar system plasmas and magnetic fields, their myriad manifestations, and their interactions with solar system bodies and their atmospheres.

Il Nuovo Cimento C, 1980

ABSTRACT

During the years 2007-2009 of solar minimum, the STEREO dual spacecraft have observed around 100 ... more During the years 2007-2009 of solar minimum, the STEREO dual spacecraft have observed around 100 shocks driven by the interaction of fast solar wind and slow moving plasma. These shocks have low-moderate Mach number (Mms 1.1 2.5) and in most cases are quasi-perpendicular (thetaBn > 45° ), with only 20 quasi-parallel (thetaBn < 45° ) shocks. As they travel the

ABSTRACT Dawn, a solar-powered, ion-propelled mission, was launched on September 27, 2007, reachi... more ABSTRACT Dawn, a solar-powered, ion-propelled mission, was launched on September 27, 2007, reaching its first target, Vesta, on July 16, 2011. Dawn orbited Vesta until September 5, 2012, and is now on its way to Ceres, where it will enter orbit in early 2015 [Fig.1].

For the last 25 years, large-scale field-aligned currents (Birkeland currents) have been consider... more For the last 25 years, large-scale field-aligned currents (Birkeland currents) have been considered the main contributor of the electromagnetic energy that powers auroral acceleration processes. However, we have found evidence for global contributions from another source. Data that were collected from the Polar spacecraft over the course of one year show that the flow of Alfven wave electromagnetic energy at geocentric distances of 4-7 Re delineates the statistical location of the auroral oval. Furthermore, the magnitude and flow direction of the Alfven wave Poynting flux suggest that this Poynting flux is a major energy contributor for auroral acceleration processes and, ultimately, for auroral emissions along the entire auroral oval. The globally occurring Alfven waves thus provide an important link in the chain of energy transfer processes from the magnetosphere to the ionosphere.

Electromagnetic ion cyclotron (EMIC) waves inside the magnetosphere have frequencies located at t... more Electromagnetic ion cyclotron (EMIC) waves inside the magnetosphere have frequencies located at the high frequency end of the ULF spectrum. These waves usually appear in wave packets, leading to their original name ``pearls''. In the past, most in situ observations of these EMIC waves were made near the equator. Thus little is known about the characteristics of these waves at mid- and high latitudes. In this study we use the observations by Polar to examine the generation mechanism and the propagation of these waves. We find that Polar data show two conditions where strong EMIC wave packets tend to occur. At magnetically quiet times, Pc 1 wave packets may be found over a wide range of L-values in the outer magnetosphere. These waves are left-handed polarized near the equator but more linearly polarized at higher latitudes. Their frequencies are controlled by the magnetic field strength at the equator. These wave characteristics suggest that they are generated near the equa...

Planetary and Space Science, 1994

In this study we use 14 years of Pioneer Venus Orbiter Electric Field Detector (OEFD) data to def... more In this study we use 14 years of Pioneer Venus Orbiter Electric Field Detector (OEFD) data to define the characteristics of (VLF) burst activity in the nightside ionosphere of Venus. Our statistical results show that there are essentially four types of VLF signals. The first type of signal is only observed in the 100 Hz channel and not in any of the higher frequency channels (730 Hz, 5.4 kHz or 30 kHz). Occurrence of these waves is controlled by the magnetic field with a weaker dependence on electron density. The occurrence of these waves is controlled by the magnetic field with a weaker dependence on electron density. The occurrence rate decreases with increasing altitude to a height of 600 km. For higher altitudes beyond 600 km the occurrence rate remains roughly constant. The statistics of these signals are what one would expect for whistler mode waves from a subionospheric source. The second type of signal is broadline wave activity appearing below 300 km in the low altitude ionosphere. These signals often occur in all four channels of the OEFD. These signals are also thought to come from a subionospheric source. The third type of signal appearing near the edge of the planetary optical shadow. They are probably ion acoustic waves generated by a current driven instability associated with plasma clouds in the wake. The fourth type of signal is a narrow band wave. It occurs in either of the two high frequency channels in the high altitude tail region, and is attributed to locally generated Langmuir waves. In addition, we also observe spacecraft interference noise in both the 100 and 730 Hz channels. These signals mainly occur near the edge of the planetary optical shadow and have an inbound and outbound asymmetry in activity.

Physics of the Earth and Planetary Interiors, 1979

Journal of Geophysical Research, 1981

Data from the fluxgate magnetometer, plasma wave experiment and Langmuir probe aboard Pioneer Ven... more Data from the fluxgate magnetometer, plasma wave experiment and Langmuir probe aboard Pioneer Venus are used to investigate the characteristic thickness length scale of the ionopause current sheet, as well as how this length scale is controlled. Thickness is found to be a bistatic quality, large scales being associated with high field strengths and current sheet altitudes below 300 km, while smaller scales are found with lower field strengths and ionopause altitudes above 300 km. Ion collisions and plasma wave activity contribute to the formation of the broader, low-altitude ionopause current sheets. Although evidence suggests that the wave activity influences the thin ionopause current sheets, a simple model points to the control of the thin ionopause current sheets by ionospheric ion and electron temperatures

Journal of Geophysical Research: Space Physics, 1992

Observations of the low‐latitude boundary layer in the subsolar region when the interplanetary ma... more Observations of the low‐latitude boundary layer in the subsolar region when the interplanetary magnetic field (IMF) is strongly northward indicate that the boundary layer consists of steplike multiple layers rather than a single diffusive layer. These sublayers can be formed by spatially limited, temporally varying reconnection near the polar cusp. In this model when the interplanetary magnetic field is strongly northward a magnetosheath flux tube reconnects in the north and south beyond the cusp. The tube shortens itself and reorients to align itself with other magnetospheric field lines and eventually be assimilated with other magnetospheric field lines. Energy from the shortening of the flux tube and the reduction of magnetic energy is transferred into the magnetosphere and increases the pressure above its initial equilibrium value while the reconnected flux tube sinks into the magnetosphere. The interchange instability is one of the possible mechanisms to disperse and expand the...

Journal of Geophysical Research, 1986

The steady state gas dynamic model of magnetosheath magnetic fields previously developed by Sprei... more The steady state gas dynamic model of magnetosheath magnetic fields previously developed by Spreiter and Stahara (1980) is generalized for the common situation of a temporally varying interplanetary field orientation. Examples for the particular case of Venus in the solar wind illustrate the application of the model to the passage of rotational discontinuities and MHD waves through planetary magnetosheaths. The results of this model illustrate how the field structure near a planetary magnetopause or ionopause can be affected by interplanetary field variations rather than by local processes because of the “pile up” of magnetosheath fields from a sequence of upstream fields. Changes in the spectrum of interplanetary waves on their transmission to the magnetopause are also indicated.

Journal of Geophysical Research: Space Physics, 2007

Shortly after 0600 UT on 7 April 2000 a tangential discontinuity (TD) in the solar wind passed th... more Shortly after 0600 UT on 7 April 2000 a tangential discontinuity (TD) in the solar wind passed the Advanced Composition Explorer satellite (ACE). It was characterized by a rotation of the interplanetary magnetic field (IMF) by ∼145° and more than a factor‐of‐2 decrease in the plasma density. About 50 min later, Polar encountered more complex manifestations of the discontinuity near noon in the magnetosheath outside the Northern Hemisphere cusp. On the basis of Polar observations, theoretical modeling, and MHD simulations we interpret the event as demonstrating that (1) a fast mode rarefaction wave was generated during the TD‐bow shock interaction, (2) the fast wave carried a significant fraction of the density change to the magnetopause while the remainder stayed with the transmitted discontinuity, and (3) magnetic merging occurred between IMF field lines within the magnetosheath on opposite sides of the discontinuity's surface as it approached the magnetopause. Before the disco...

Journal of Geophysical Research: Space Physics, 1993

The magnetic structure and energy dissipation at low‐Mach‐number, quasi‐parallel collisionless sh... more The magnetic structure and energy dissipation at low‐Mach‐number, quasi‐parallel collisionless shocks are examined through observations obtained by the ISEE 1 and 2 spacecraft at seven crossings of the Earth's dayside bow shock. The Alfvén Mach number of the shocks in this set ranges from 2.0 to 3.7, and the angle θBn between the shock normal and the average upstream magnetic field direction ranges from 2° to 39°. The shocks all exhibit a fairly short‐scale‐length ramp where the principal jumps in the electron temperature, ion temperature, and magnetic field strength take place. Large‐amplitude, low‐frequency, transverse waves in the magnetic field are present in and downstream from the ramp, with more modest waves upstream. The amplitude of the downstream waves is typically larger than can be accounted for by shock compression of the upstream waves. The electron heating represents about 6% of the dissipated bulk flow energy, consistent with observations in other parameter regim...

Journal of Geophysical Research: Space Physics, 1983

The energies of the field‐aligned proton beams observed upstream of the earth's bow shock are... more The energies of the field‐aligned proton beams observed upstream of the earth's bow shock are tested, on a statistical basis, against a simple reflection model. The comparison is carried out using both plasma and magnetic field data collected by the ISEE 2 spacecraft. The observations refer to the period from November 5 to December 20, 1977. According to this model, some of the solar wind protons incident upon the earth's shock front when reflected upstream gain energy by displacement parallel to the interplanetary electric field. The energy gained in the reflection can be described as a function of the angles between the interplanetary magnetic field, the solar wind bulk velocity, and the local shock normal. The task of finding these angles, i.e., the expected source point of the reflected ions at the earth's shock front, has been resolved using both the measured magnetic field direction and the actual beam trajectory. The latter method, which takes into account the ion...

Journal of Geophysical Research: Space Physics, 1982

Plasma and magnetic field data from ISEE 1 and 2 are examined for 5 passes of the magnetopause re... more Plasma and magnetic field data from ISEE 1 and 2 are examined for 5 passes of the magnetopause region at 20°–40° northern latitudes and ∼0800 to 1215 hours local time. These intervals contained a total of 15 well‐defined magnetic flux transfer events, which occurred in the magnetosheath as well as the magnetosphere. In either case, flux transfer events are characterized by a mixture of magnetosheath and magnetospheric particles. This fact strongly supports the hypothesis that flux transfer events represent encounters of reconnected flux tubes. Inside all of the studied events, the magnetic field strength as well as the sum of plasma and magnetic pressures is strongly enhanced. This excess pressure appears to be balanced by the tension of the ambient magnetic field lines as they are draped around the reconnected flux tube. The different observed magnetic field signatures are consistent with expectations for encounters of the flux tubes at different relative locations. Only those even...