Ulysses observations of a ``density hole'' in the high-speed solar wind
Abstract
Ulysses observations at mid and high heliographic latitudes have revealed a solar wind devoid of the large variations in density, temperature, and speed that are commonly observed at low latitudes. One event, however, observed on May 1, 1996, while Ulysses was located at ~3.7AU and 38.5°, stands out in the plasma data set. The structure, which is unique in the Ulysses high-latitude data set, is seen as a drop in proton density of almost an order of magnitude and a comparable rise in proton temperature. The event lasts ~3<fraction shape="case" style="single" align="center"><num>1</num><den>2</den></fraction> hours giving the structure a size of ~9.6×106km (0.06 AU) along the spacecraft trajectory. Minimum variance analysis of this interval indicates that the angle between the average magnetic field direction and the minimum variance direction is ~92°, suggesting that the ``density hole'' may be approximated by a series of planar slabs separated by several tangential discontinuities. We discuss several possible explanations for the origin of this structure, but ultimately the origin of the density hole remains unknown.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- February 1998
- DOI:
- 10.1029/97JA02142
- Bibcode:
- 1998JGR...103.1933R
- Keywords:
-
- Ulysses Mission;
- Solar Wind Velocity;
- Solar Protons;
- Plasma Density;
- Solar Magnetic Field;
- Coronal Holes;
- Plasma Temperature;
- Proton Density (Concentration);
- Interplanetary Physics: Solar wind plasma;
- Interplanetary Physics: Sources of the solar wind;
- Solar Physics;
- Astrophysics;
- and Astronomy: Corona;
- and Astronomy: Coronal holes