Fe/O ratio behavior as an indicator of solar plasma state at different solar activity manifestations and in periods of their absence

Abstract

Abstract. We report the results of the investigation into plasma physical characteristics at various solar activity manifestations and in periods of their absence. These results have been obtained from quantitative estimates of the relative abundance of Fe and O ions in different energy ranges. Maximum values of the Fe/O ratio is shown to correspond to particle fluxes from impulsive flares for ions with energies <2 MeV/n (the most significant manifestation of the first ionization potential (FIP) effect). In particle fluxes from gradual flares, the Fe/O value decreases smoothly with ion energy and is noticeably inferior to values of fluxes in impulsive events. We have established that the properties of flares of solar cosmic rays indicate their belonging to a separate subclass in the total population of gradual events. Relying on Fe/O variations, we propose an explanation of the solar plasma behavior during the development of flares of both classes.Magnetic clouds (a separate class of coronal mass ejections (CME)), which have turbulent compression regions and are sources of strong geomagnetic storms, exhibit a relative composition of Fe ions comparable to the abundance of Fe in ion fluxes from gradual flares.We have found out that the Fe/O value can be used to detect penetration of energetic flare plasma into the CME body at the initial phase of their joint development and to estimate its relative contribution.During solar minimum with complete absence of sunspots, the Fe/O ratio at a distance of 1 AU show absolutely low values of Fe/O=0.004-0.010 in the energy range from 2-5 to 30 MeV/n. This is associated with the manifestation of the cosmic ray anomalous component, which causes an increase in the intensity of ion fluxes with a high FIP, including oxygen (O), and elements with a low FIP (Fe) demonstrate weakening of the fluxes. As for particles with higher energies (E k >30 MeV/n), the Fe/O increase is due to the decisive influence of galactic cosmic rays on the composition of admixtures in the solar wind under solar minimum conditions. The abundance of heavy elements in galactic cosmic rays 30-500 MeV/n is similar to values in fluxes from gradual flares during high solar activity.During solar minimum without sunspots, the Fe/O behavior for different ion energy ranges in plasma flows from coronal holes (CH) and in the solar wind exhibits only minor deviations. At the same time, plasma flow associated with the disturbed frontal CH region can be sources of moderate geomagnetic storms.