Gilbert D. Mead

Space-Age Geodesy: The NASA Crustal Dynamics Project

The NASA Crustal Dynamics Project has deployed satellite laser ranging (SLR) systems and very-long-baseline-interferometer (VLBI) systems for measurements of global and regional crustal motions and Earth rotation parameters. In 1984, the several year buildup of the network approached full capability. During 1984, the SLR systems measured 142 unique baselines between stations for the purpose of determining plate motion between the North American, Pacific, South American, Nazca, Australian, and Eurasian plates; 31 baselines for internal deformation of the same plates; and 9 baselines for regional deformation in the area of the western North American plate boundary. During 1984, the VLBI systems measured 24 baselines for plate motion between the North American, Pacific, and Eurasian plates; 37 baselines for internal deformation of the same plates; and 101 baselines for regional deformation in the area of the western North American plate boundary. Both the SLR and VLBI stations operated throughout the September 1983 to October 1984 international MERIT campaign of measurements of the Earths polar motion and changes in rotation rate. NASAs future plans are to continue these measurements through at least 1990 and to initiate a joint NASA/ European SLR measurement campaign for determining regional crustal deformation in the Mediterranean area.

Pogo and Pangaea

Abstract Long wavelength magnetic anomalies of crustal origin derived from the POGO and MAGSAT satellite data often display a strong continuity across the now-rifted continental margins when the continents are reassembled into Pangaea. These anomalies predate the breakup of the supercontinent and represent major blocks whose crustal properties are broadly similar even though those blocks are no longer contiguous.

Jupiter's Radiation Belts: Can Pioneer 10 Survive?

Model calculations of Jupiters electron and proton radiation belts indicate that the Galilean satellites can reduce particle fluxes in certain regions of the inner magnetosphere by as much as six orders of magnitude. Average fluxes should be reduced by a factor of 100 or more along the Pioneer 10 trajectory through the heart of Jupiters radiation belts in early December. This may be enough to prevent serious radiation damage to the spacecraft.

The motion of trapped particles in a distorted field.

The motion of charged particles in a geomagnetic field distorted by the solar wind is examined, using adiabatic theory. It is shown that the drift motion of particles trapped on high L-shells depends strongly on their equatorial pitch angle. Those mirroring near the equator move in on the night side, while those mirroring at low altitudes move out, thus producing a significant Splitting of the L-shell with pitch angle. One consequence is that the very high latitude lines on the day side may contain trapped particles near the equator, but none near the ends of the lines. The opening up of field lines in the geomagnetic tail may be the Controlling factor governing the high-latitude limit of trapping on both the day side and the night side.

Neutral points on the boundary of the closed magnetosphere

Theoretical studies of a field-free plasma incident upon a magnetic dipole lead to a closed magnetosphere with two neutral points in the noon magnetic meridian, at a latitude of ± 70°–75° and a geocentric distance of approximately 10 RE. The position of the neutral points with respect to the dipole axis is not greatly affected by the angle of incidence of the solar wind. Although the field magnitude near the neutral points is only a fraction of the dipole field, the direction is seen to reverse on opposite sides of the neutral point. Near the boundary the field direction is parallel to the boundary and tends to point towards the neutral point in the Northern hemisphere.

LOW-ENERGY CHARGED PARTICLE ENVIRONMENT OF THE EARTH

Survey in satellite era of energetic particle radiations, plasmas and magnetic fields in space including solar wind, solar cosmic rays, etc