Fast prograde coronal flows in Sun-as-a-star EUV

We report the discovery and characterization of high-speed (10-100 km/s) flows detected in EUV emission lines characteristic of active regions. These findings use Sun-as-a-star spectroscopy in the range 33-103~nm provided by the EVE/MEGS-B spectrometer on the Solar Dynamics Observatory. This instrument has spectral binning at 0.04~nm, but we find that the data have great stability and low line-centroid noise levels, well below 1~pm for relative measurements over 1-h sampling. This corresponds to Doppler signals of less than 1~km/s, substantially smaller than the diurnal signal produced by SDO’s geosynchronous orbital motion.EVE detects this orbital motion cleanly in low-excitation lines such as Lyman-gamma. In higher-excitation lines we see ubiquitous high-speed Doppler signatures, variable on active-region time scales of days, and increasing in amplitude with temperature of formation. The flows show amplitudes as large as 80~km/s in Si XII (52.1 nm, log(T) = 6.9) in October-December 2010, for example, and are consistent with prograde coronal motions: redshifted at the W limb and blueshifted at the E limb. The Doppler shifts correlate well with AIA-derived image distributions.