Description of the Solar Wind Ion Survey Spectrogram

The responses of the Solar Wind Ion Analyzer were averaged for about 50 minutes. For each of the 32 E/Q passbands, the responses of all twelve sensors in all sectors were scanned, and the peak response for each passband was determined. The logarithm (base 10) of each of these responses was color coded and displayed in the Energy-time spectrogram.

Velocity moments of these averaged distribution functions were integrated to obtain the ion number density and flow velocity:

The number density is plotted in the second panel and the magnitude of the flow velocity is shown in the third panel. The polar angles of the flow velocity, ø (ø = 180° is anti-sunward) and ( is the S/C spin plane) are plotted in the fourth panel.

The kinetic temperature was computed from the distribution function by integrating:

The CPI solar wind ion analyzer is an E/Q analyzer and the initial distribution functions were calculated assuming that the plasma is H⁺. Care must be taken when multi-component plasmas are present. If He⁺⁺ is present and is flowing with the same speed as the H⁺ component, it will contribute to the distribution function at twice the velocity (four times the energy) of the H⁺. To facilitate the automated processing of these data the above integral was evaluated between |v_min| = 171 km/s and |v_max| = 1.35 × |u|. The resulting temperatures produce excellent fits to the observations. When He⁺⁺ is present the distribution functions are consistent with an He⁺⁺ temperature, T_He⁺⁺ = 4 × T_H⁺, i.e., the H⁺ and He⁺⁺ have similar thermal velocities.