SPA-GRL Issue Highlights

Perry et al. use the "frozen-in" ionization state of solar wind iron (Fe) ions as a tracer to study the transport of solar plasma material to the cusp during a coronal mass ejection (CME) event that occurred May 1-3, 1998, a period of high solar activity. Fe ions were significantly enriched during the CME. The authors compare for the first time ion composition data from the Advanced Composition Explorer spacecraft and measurements from the Polar spacecraft at high latitudes in the region of the mid-altitude northern cusp. A good correlation between the measurements from the two satellites indicates that during periods of southward interplanetary magnetic field direct entry of solar wind material occurred.

To better understand the magnetic field observations made by the Mars Global Surveyor, Purucker et al. invert a global distribution of radial magnetic field observations which they then use to produce an altitude-normalized map of the field at 200 km. Focussing on observations taken below 200 km altitude, the authors find good correlations between their observations and tectonics, and suggest that a major change in crustal properties is associated with faulting. They find some significant magnetic features in young, sparsely cratered plains, and suggest that these terrains represent thin cover over ancient terrains.

Pickup ions modify the solar wind flow in the outer heliosphere, especially beyond 30 AU. Wang et al. use observations from Voyager 2 and Ulysses to investigate the effect of these ions. (The spacecraft were at the same latitude in the southern heliosphere at the beginning of 1999.) The authors input hourly average data from Ulysses for the period 1998-1999 into a one-dimensional numerical model, map the evolution of solar wind to the location of Voyager 2 (currently at a distance beyond 60 AU), and compare the numerical output for 1999 with the spacecraft's observations. They calculate that the pickup ions decrease the solar wind speed by ~ 40 km/s near 60 AU, and deduce the interstellar neutral hydrogen density to be 0.05 cm-3.

Using measurements made by the Geotail satellite in 1995-1998 of energetic low-charge-state heavy ions (LCSHI) sunward of Earth's bow shock, Christon et al. find that the LCSHI are often accompanied by sunward energetic electron bursts and by enhanced interplanetary magnetic field (IMF) fluctuations. Intervals of strong LCSHI flux tend to occur when geomagnetic conditions are perturbed. The authors identify energetic ionospheric origin ions, O+1, N+1 and O+2, in the upstream region; these ions stream sunward away from the Earth along generally radial IMF, and are more common than previously thought.