Abundance Variation at the Vicinity of an Active Region and the Coronal Origin of the Slow Solar Wind

Abstract

The solar wind ion composition is generally frozen-in within 5 R☉ of the Sun. Many characteristics in the elemental abundances measured in the solar wind are believed to be set at the chromospheric and low coronal levels. By connecting plasma parameters in the coronal and in situ solar wind data, valuable insights can be obtained as to how and where the solar wind is produced. Elemental abundance is found to vary across solar structures and heliocentric heights, as well as in the solar wind. Therefore, solar wind elemental composition data (such as those from SWICS on board ACE), combined with spectroscopic observations of the inner corona (such as those from UVCS on board SOHO), are ideal for investigating the coronal origin of the solar wind. We present such joint analysis using data from SOHO UVCS and ACE SWICS. In 1999 October, UVCS observed the west limb corona at 1.64 R☉ for 7 days with the passing of an equatorial coronal hole followed by an active region complex. This corresponds to a rarefaction transition from fast to slow wind as measured by ACE. This presents an unprecedented opportunity for comparing the variations in the coronal plasma properties with those in the solar wind. We present the analysis for the electron temperature, density, and elemental abundances during this period. We compare these properties between the two data sets and discuss the implications on the formation region of the slow solar wind. Treatment of the line-of-sight effect in the UVCS data, along with 3D MHD coronal field models, are employed to connect the coronal and solar wind data.