Flows and Nonthermal Velocities in Solar Active Regions Observed with the EUV Imaging Spectrometer onHinode: A Tracer of Active Region Sources of Heliospheric Magnetic Fields?

Abstract

From Doppler velocity maps of active regions constructed from spectra obtained by the EUV Imaging Spectrometer (EIS) on the Hinode spacecraft we observe large areas of outflow (20-50 km s -->−1) that can persist for at least a day. These outflows occur in areas of active regions that are faint in coronal spectral lines formed at typical quiet-Sun and active region temperatures. The outflows are positively correlated with nonthermal velocities in coronal plasmas. The bulk mass motions and nonthermal velocities are derived from spectral line centroids and line widths, mostly from a strong line of Fe XII at 195.12 A. The electron temperature of the outflow regions estimated from an Fe XIII to Fe XII line intensity ratio is about -->(1.2–1.4) × 106 K. The electron density of the outflow regions derived from a density-sensitive intensity ratio of Fe XII lines is rather low for an active region. Most regions average around -->7 × 108 cm -->−3, but there are variations on pixel spatial scales of about a factor of 4. We discuss results in detail for two active regions observed by EIS. Images of active regions in line intensity, line width, and line centroid are obtained by rastering the regions. We also discuss data from the active regions obtained from other orbiting spacecraft that support the conclusions obtained from analysis of the EIS spectra. The locations of the flows in the active regions with respect to the longitudinal photospheric magnetic fields suggest that these regions might be tracers of long loops and/or open magnetic fields that extend into the heliosphere, and thus the flows could possibly contribute significantly to the solar wind.