Elemental Fractionation in the Slow Solar Wind

Abstract

Slow solar wind, found at low heliographic latitudes, and fast solar wind, associated with high-latitude coronal holes, are fundamentally different: slow solar wind is more variable and is biased in elements with low first ionization potentials (FIPs), whereas fast solar wind is steady and has at most limited FIP bias. It has been recently argued that these differences are consequences of a continuous reorganization of the Sun's magnetic field described by a new heliospheric magnetic field model. This continuous reorganization requires a sustained reconnection process at low latitudes between open magnetic field lines and large coronal loops. Arguably, the slow solar wind originates from material stored on large coronal loops which is released sporadically because of reconnection. The fast solar wind is released on continuously open magnetic field lines. In this paper a theory for FIP fractionation is developed which depends on the wave heating of minor ions which extends below the transition region. The wave heating may be natural on the closed field configurations of large coronal loops but not in the open configurations associated with fields emanating from coronal holes. Therefore, the theory naturally leads to a differentiation in FIP fractionation between fast and slow solar wind.