Magnetospheric electric field measurements during sudden commencements

Direction measurements of electric fields were made in the outer magnetosphere during two sudden commencements in 1972. These measurements were observed with the double floating probe experiment carried aboard the IMP 6 satellite. The initial variations of the measured electric field consisted of an increase from a background of about 1 mv/meter to some 10 mv/meter at about 7 rE (earth radi) and to some 4 mv/meter at 3 rE. These initial electric field disturbances were longitudinal, oriented counter clockwise about an axis pointed north. A solution of Maxwell's third equation is derived for these measurements using a quasi-static version of Mead's model of the magnetosphere B (t). This solution seems to describe well the magnitude and direction of the initial perturbation of the electric field vectors observed during these two sudden commencements. After the initial increase, the measured electric field rings several times with periods of the order of minutes. This observed oscillatory behavior correlates with magnetic observatory records taken near the foot of the magetic field line passing through the satellite

Early results from ISEE-A electric field measurements

In the solar wind and in middle latitude regions of the magnetosphere, spacecraft sheath fields obscure the ambient field under low plasma flux conditions such that valid measurements are confined to periods of moderately intense flux. Initial results show: (1) that the DC electric field is enhanced by roughly a factor of two in a narrow region at the front, increasing B, edge of the bow shock, (2) that scale lengths for large changes in E at the subsolar magnetopause are considerably shorter than scale lengths associated with the magnetic structure of the magnetopause, and (3) that the transverse distribution of B-aligned E-fields between the outer magnetosphere and ionospheric levels must be highly complex to account for the random turbulent appearance of the magnetospheric fields and the lack of corresponding time-space variations at ionospheric levels. Spike-like, non-oscillatory, fields lasting less than 0.2 seconds are occasionally seen at the bow shock and at the magnetopause and also intermittently appear in magnetosheath and plasma sheet regions under highly variable field conditions

The spherical probe electric field and wave experiment

The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonlinear processes that result in acceleration of plasma, and the analysis of large scale phenomena where all four spacecraft are needed

On ionospheric composition measurements with an R.F. impedance probe

Consideration is given to extending various methods used for determining electron number density in the ionosphere to ion composition measurements. A technique involving the impedance of an antenna operated in a frequency range on the order of the ion cyclotron frequency to the electron cyclotron frequency appears promising. Theoretical impedance results for some idealized combinations of ions as well as typical ion mixtures encountered in the ionosphere illustrate application of the technique. The advantages and limitations of the impedance probe are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32914/1/0000294.pd

Evolution of the proton ring current energy distribution during 21–25 April 2001 storm

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95267/1/jgra18324.pd

Transport of the plasma sheet electrons to the geostationary distances

The transport and acceleration of low‐energy electrons (50–250 keV) from the plasma sheet to the geostationary orbit were investigated. Two moderate storm events, which occurred on 6–7 November 1997 and 12–14 June 2005, were modeled using the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM) with the boundary set at 10  R E in the plasma sheet. The output of the IMPTAM was compared to the observed electron fluxes in four energy ranges (50–225 keV) measured by the Synchronous Orbit Particle Analyzer instrument onboard the Los Alamos National Laboratory spacecraft. It was found that the large‐scale convection in combination with substorm‐associated impulsive fields is the drivers of the transport of plasma sheet electrons from 10  R E to geostationary orbit at 6.6  R E during storm times. The addition of radial diffusion had no significant influence on the modeled electron fluxes. At the same time, the modeled electron fluxes are one (two) order(s) smaller than the observed ones for 50–150 keV (150–225 keV) electrons, respectively, most likely due to inaccuracy of electron boundary conditions. The loss processes due to wave‐particle interactions were not considered. The choice of the large‐scale convection electric field model used in simulations did not have a significant influence on the modeled electron fluxes, since there is not much difference between the equipotential contours given by the Volland‐Stern and the Boyle et al . (1997) models at distances from 10 to 6.6  R E in the plasma sheet. Using the TS05 model for the background magnetic field instead of the T96 model resulted in larger deviations of the modeled electron fluxes from the observed ones due to specific features of the TS05 model. The increase in the modeled electron fluxes can be as large as two orders of magnitude when substorm‐associated electromagnetic fields were taken into account. The obtained model distribution of low‐energy electron fluxes can be used as an input to the radiation belt models. This seed population for radiation belts will affect the local acceleration up to relativistic energies. Key Points Transport of plasma sheet electrons due to convection and substorms Importance of boundary conditions in plasma sheet Importance of magnetic field model choicePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97187/1/jgra50047.pd

Entropy mapping of the outer electron radiation belt between the magnetotail and geosynchronous orbit

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94614/1/jgra21264.pd