Iron charge state distributions as an indicator of hot ICMEs: Possible sources and temporal and spatial variations during solar maximum

Abstract

It has been shown that Fe charge states greater than and equal to 16 are often observed in the presence of interplanetary coronal mass ejections (ICMEs) at 1 AU. These elevated charge states, representative of hot source regions on the Sun, provide an identifier of ICMEs independent of expansion processes and heliocentric distance. Using this new identifier, we present a comparative study of Fe charge state distributions as a function of latitude and time. We compare Fe charge state data from the ACE spacecraft in the ecliptic plane with that from the Ulysses spacecraft along its orbit from low to high latitudes. We discuss the frequencies of high Fe charge state distributions through a range of latitudes on the approach toward solar maximum. Close to solar maximum, we find almost an order of magnitude fewer hot ICMEs at higher latitudes than in the ecliptic. We offer an explanation for the existence of high Fe charge states in hot ICMEs as a result of magnetic connectivity to flaring regions.