J. Geophys. Res. - Space Physics - Vol. 103 , No. A8 , p. 17,205
The Proton Monitor, a small subsensor in the CELIAS/MTOF experiment on the SoHO spacecraft, was designed to assist in the interpretation of measurements from the high mass resolution main MTOF sensor. In this paper we demonstrate that the Proton Monitor data may be used to generate reasonably accurate values of the solar wind proton bulk speed, density, thermal speed, and north/south flow direction. Correlation coefficients based on comparison with the solar wind measurements from the SWE instrument on the WIND spacecraft range from 0.87 to 0.99. Based on the initial 12 months of observations, we find that the proton momentum flux is almost invariant with respect to the bulk speed, confirming a previously published result. We present observations of two interplanetary shock events, and of an unusual solar wind density depletion. This large density depletion, and the correspondingly large drop in the solar wind ram pressure, may have been the cause of a nearly simultaneous large increase in the flux of relativistic magnetospheric electrons observed at geosynchronous altitudes by the GOES 9 spacecraft. Extending our data set with a 10-year time span from the OMNIWeb data set, we find an average frequency of about one large density depletion per year. The origin of these events is unclear; of the 10 events identified, 3 appear to be corotating and at least 2 are probably CME-related. The rapidly available, comprehensive data coverage from SoHO allows the production of near real time solar wind parameters that are now accessible on the World Wide Web.