Solar Wind Iron Charge States Observed With High Time Resolution With CELIAS/CTOF

M.R. Aellig, H. Grünwaldt, P. Bochsler, P. Wurz, S. Hefti, R. Kallenbach, F.M. Ipavich, D. Hovestadt, M. Hilchenbach, and the CELIAS Team

Paper presented at the 5th SOHO Workshop, 17-20 June, 1997, Oslo, Norway

The SOHO/CELIAS/CTOF (Charge Time Of Flight) mass spectrometer measures the ionic and elemental composition of minor ions in the solar wind. From Fe charge spectra we derive the so-called freeze-in temperature with a time resolution of five minutes. Changes in coronal electron temperature as well as in density manifest themselves in a variation of freeze-in temperatures, making the latter a powerful tool for remote coronal diagnostics. Unlike dynamic solar wind properties (velocity, density, kinetic temperature, etc.) the freeze-in temperature of minor ions does not alter on the way from the inner corona to 1 AU. Variations are observed on timescales down to several hours, sometimes without any substantial change in solar wind plasma parameters. Applying basic plasma diffusion equations, we conclude that the temporal variations in freeze-in temperature are best explained in terms of spatial changes in coronal conditions. These observations confirm that the filamentary structures of the inner corona observed in H-alpha survive in the interplanetary medium at least out to 1 AU. Furthermore, we emphasize the prospect to map the in situ measured freeze-in temperature back to individual coronal phenomena which are accessible to optical observation.

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Last Update: May 16, 1997, Peter Wurz