Abstract. The proton monitor, a small subsensor in the Charge, Element, and Isotope Analysis System/Mass Time-of-Flight (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. On the basis of 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. IntroductionThe The proton monitor is a subsensor of the MTOF experiment. MTOF determines high-resolution mass spectra of heavy solar wind ions and uses a very wide bandwidth energyper-charge analyzer to maximize counting statistics (at the expense of charge state information) for rare elements and isotopes. Since SOHO is not a spinning spacecraft, the deflection system was designed to have a wide angular acceptance in two dimensions. The PM was designed to assist in the interpretation of MTOF data and for that reason uses a similar wide bandwidth (and wide angular acceptance) analyzer that 17,205
Chromium and iron are two heavy elements in the solar wind with similar masses. The MTOF (Mass Time Of Flight) sensor of the CELIAS investigation on the SOHO spacecraft easily allows these two elements to be resolved from one another. Taking the ratio of the densities of these two elements-as opposed to considering their absolute abundances-minimizes the effects of uncertainties in instrument efficiency. Measurements of the abundance ratio are presented here. The First Ionization Potential (FIP) of chromium is 6.76 eV, while the FIP of iron is 7.87 eV. Since Cr and Fe have similar FIPs the ratio of their abundances should not be biased by the FIP effect which is well known in different solar wind flows. Therefore the Cr/Fe ratio from the MTOF data should give a good measure of the photospheric abundance ratio. We also compare the ratio measured in this work to the meteoritic value.
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