Elemental Fractionation of the Solar Wind as Indicators of Coronal Source Regions and Physical Processes.

Abstract

Heavy ions in the solar wind record the history of physical events occurring to a given parcel of plasma during its escape from the solar atmosphere. Heating, acceleration, and interactions with waves, particles, and magnetic fields all imprint their signatures in the elemental composition and ionic charge states of heavy ions which carry the information unchanged from a few solar radii all the way to the edge of the heliosphere. Therefore by studying heavy ions in the solar wind near-Earth, we are able to peer back into the corona and gain valuable insight concerning physical processes within a region currently inaccessible to direct satellite exploration.

Understanding how mass and energy is released from the Sun and transported into interplanetary space is of increasing importance to our modern society which depends on space-based technology for global navigation and communications. In this work we explore the source regions, release and acceleration mechanisms, and elemental fractionation of the slow solar wind. In particular we seek to answer the following questions: (1) “How much plasma, if any, do the largest coronal loops contribute to the solar wind?”, (2) “Where and how does closed filed plasma escape into the solar wind and become accelerated?”, and (3) “What are the physical conditions and time scales required for gravitational settling?”. Towards these ends, we delve into over 20 years of solar wind data from two nearly identical Solar Wind Ion Composition Spectrometer (SWICS) instruments which flew onboard the Ulysses (1990 – 2009) and Advanced Composition Explorer (ACE; 1998 - present) spacecraft. We utilize novel analysis methods and discover the existence of a new class of solar wind events which we call “heavy ion dropouts”. These dropouts have distinctive, mass-fractionated elemental composition indicative of specific coronal conditions and probable source regions. By analyzing the temporal and spatial variability of heavy ion dropouts and comparing our observations to basic simulations of the solar corona, we are able to provide fresh insight which may be used to constrain, validate, and refine prevailing solar wind theories.