Ulysses Solar Wind Observations Over the Poles of the Sun (SWOOPS) Proton Particle Distribution Functions, Level H2, 4 min Data

This File contains the Distribution Function of Protons. DATA REDUCTION: The SWOOPS (Solar Wind Observations Over the Poles of the Sun) Ion Instrument is a Spherical-Section Curved-Plate Electrostatic Analyzer. Particle Arrival Directions are measured in Spacecraft Coordinates of Azimuth (scanned by Spacecraft Rotation) and Elevation (determined by the Detector Number) Angles. The Spacecraft Spin Axis was oriented toward the Earth. The Energy/Charge (E/q) Resolution was about 2.5% while the Azimuth (Phi) and Elevation (Theta) Resolutions were both ~5.6°. A Description of the SWOOPS is given in a Paper by S.J. Bame, D.J. McComas, B.L. Barraclough, J.L. Phillips, K.J. Sofaly, J.C. Chavez, B.E. Goldstein, and R.K. Sakurai, Astronomy and Astrophysics Supplement Series, Ulysses Instruments Special Issue, Vol. 92, No. 2, p.237-265, 1992. The Number of Counts in each E/q-Phi-Theta Bin were examined to determine the Peak of the Proton and Alpha Particle Distribution, respectively, and the Vector Magnetic Field (in Spacecraft Coordinates) was obtained for the Time at which the Peak was measured. A "coarse" Two-Dimensional Matrix was then formed by rotating the Data into a Coordinate System with Axes parallel and perpendicular to the Field Direction. Note that Gyrotropy is assumed in making that Transformation. The Resolution of the Matrix is "coarse" because the Vector Velocity assigned to each Bin was taken to be at the Center of the Bin. In reality, the Counts in each Bin were probably not smoothly distributed in Velocity Space over the Bin, but were weighted toward the Part of the Bin nearest the Center of the Peak of the Velocity Distribution. The "coarse" Distribution would thus yield Values for the Density and Temperature that were higher than the true Values. A Correction for that effect was accomplished by fitting Contours to the coarse Distribution, breaking each Bin or Pixel into Subpixels, and then using the Contours and the calibrated Angular Responses to distribute the Counts among the Subpixels. New Contours were then computed and the Process was continued until it converged. More Details about this Deconvolution of the Angular Data are given in the Appendix of a Paper by Neugebauer, M., et al., "Ion distributions in large magnetic holes in the fast solar wind" J. Geophys. Res., 106, 5635, 2001. This Procedure generated the Matrix of Velocity Distribution Functions of Protons and Alpha Particles parallel and perpendicular to the simultaneously measured Magnetic Field.