Gary W. Hoogeveen

Ulysses solar wind plasma observations from pole to pole

We present Ulysses solar wind plasma data from the peak southerly latitude of −80.2° on 12 September 1994 through the corresponding northerly latitude on 31 July 1995. Ulysses encountered fast wind throughout this time except for a 43° band centered on the solar equator. Median mass flux was nearly constant with latitude, while speed and density had positive and negative poleward gradients, respectively. Solar wind momentum flux was highest at high latitudes, suggesting a latitudinal asymmetry in the heliopause cross section. Solar wind energy flux density was also highest at high latitudes.

Experimental constraints on pulsed and steady state models of the solar wind near the Sun

Ulysses observations of the high-latitude solar wind were combined with Spartan 201 observations of the corona to investigate the nature and extent of uncertainties in our knowledge of solar wind structure near the Sun. In addition to uncertainties stemming from the propagation of errors in density profiles inferred from coronagraph observations [see, e.g., Lallement et al., 1986], an assessment of the consequences of choosing different analysis assumptions reveals very large, fundamental uncertainties in our knowledge of even the basics of coronal structure near the Sun. In the spirit of demonstrating the nature and extent of these uncertainties we develop just one of a generic class of explicitly time-dependent and filamentary models of the corona that is consistent with the Ulysses and Spartan 201 data. This model provides a natural explanation for the radial profiles of both the axial ratios and apparent radial speeds of density irregularities measured at radial distances less than 10 Rs using the interplanetary scintillation technique.

Properties of arc‐polarized Alfvén waves in the ecliptic plane: Ulysses observations

Ulysses observations of the interplanetary magnetic field reveal well-ordered rotations on the timescale of several hours. These have been previously identified as arc-polarized Alfven waves. Rotational discontinuities (RDs) are often an integral part of the wave. This study focuses on a statistical description of these rotations (ARCs) in the ecliptic plane. It is found that (1) most ARCs are limited to 180° or less in rotation ; (2) these ARCs account for between 5 and 10% of the total data set ; (3) there appears to be no preferred helicity ; (4) the minimum-variance direction typically makes a large oblique angle with the average magnetic field (), while the intermediate-variance direction is loosely aligned with ; (5) most of the events display a small but significant nonzero magnetic field component in the direction of minimum variance ; (6) the cross helicity of the ARCs tends to be higher than during non-ARC intervals ; (7) there are 2.4 times more discontinuities during ARC intervals than during non-ARC intervals ; (8) essentially all ARCs are propagating outward in the rest frame of the solar wind plasma ; and (9) there is no simple relationship between the rate of occurrence of the ARCs and heliocentric distance. Comparing these results with the predicted signatures of a number of models, it is found that arc-polarized Alfven waves with embedded RDs propagating along the minimum-variance direction best fit the majority of events.

The Triton-Neptune plasma interaction

The Voyager 2 encounter with Neptune and Triton in August 1989 showed a large ionosphere at Triton. Subsequent studies have tried to explain the production of such high levels of ionization but have ignored the possible plasma dynamics originating from the interaction between Neptunes magnetosphere and Triton. This study applies knowledge gained from studying the solar wind-Venus interaction to this case. We find that observations made by Voyager 2 can be explained by downward convection of magnetospheric plasma into Tritons atmosphere, with the flow momentum transferred to the neutral atmosphere near an altitude of 650 km. We show that momentum transfer is accomplished as both the convective velocity and the magnetic field go to zero. The mechanism by which the ionosphere is produced was identified previously as impact ionization from hot electrons originating in Neptunes magnetosphere. These precipitating hot electrons are shown in this study to be unaffected by a magnetic field below roughly 650 km. This is a result not previously anticipated, and one which implies that the plasma interaction between Neptunes magnetosphere and Triton cannot be ignored.

Radio interferometer measurements of plasmasphere density structures during geomagnetic storms

The Los Alamos plasmaspheric drift radio interferometer is a ground-based array that regularly measures periodic disturbances in the plasmasphere. These plasmaspheric density structures have been shown to depend on geomagnetic activity, as indicated by Kp. However, a direct storm time analysis of their behavior has not been done. This paper studies the amplitude, drift velocity, and location of these structures before, during, and after the onset of major geomagnetic storms. Distinct large-amplitude, storm time signatures are found during the first night after onset, continuing through the third night; there were significantly more storm time signatures during nighttime than daytime. The L shells on which the disturbances existed were found to decrease after storm onset, indicating a possible shrinking of the plasmasphere.

The Search for Solar Gravity-Mode Oscillations in the Solar Wind Using it Ulysses Plasma Data

AbstractA recent report that energetic particles measured in the solar wind may be influenced by solar gravity-mode (

Total-electron-content signatures of plasmaspheric motions

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Observations of inner plasmasphere irregularities with a satellite‐beacon radio‐interferometer array

-mode) oscillations motivated the search for