Solar Coronal Holes and Open Magnetic Flux

Abstract:

Using SDO/AIA and STEREO/EUVI EUV data in conjunction with an instrument-specific adaptive intensity thresholding algorithm, we are able to track coronal hole boundaries across the entire solar surface at a cadence of 12 hours. SOHO/EIT provides earlier era data, allowing the building EUV coronal hole maps over the course of a solar rotation. We find that for solar cycle 23 the unsigned magnetic flux enclosed by coronal hole boundaries ranges from (2-5)x10^{22} Mx, covering 5%-17% of the solar surface. For solar cycle 24 this flux ranges from (2-4)x10^{22} Mx, covering 5%-10% of the solar surface. Using a surface flux transport model, we compare observational coronal hole boundaries and computed potential open field for solar cycles 23 and 24. From both our observed coronal holes and modeled open magnetic field, we find that low-latitude regions are significant in area, contributing to the total open magnetic flux, and should be considered in more significant detail.