Temporal variability of active region outflows

Abstract

Recent observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode have shown that low-density areas on the periphery of active regions are characterized by strong blueshifts in the emission of spectral lines formed at 1MK. These Doppler shifts have been associated with outward propagating disturbances observed with extreme-ultraviolet and soft X-ray imagers. Since these instruments can have broad temperature responses, we investigate these intensity fluctuations using the monochromatic imaging capabilities of the EIS wide slit (slot) and confirm their 1MK nature. We also look into their spectral temporal variability using narrow slit observations and present the first Doppler movies of the outflow regions. We find that the Fe XII 195.119 blueshifted spectral profiles at their footpoints exhibit transient blue wing enhancements on timescales as short as the 5 minute cadence. We have also looked at the fan peripheral loops observed at 0.6MK in Si VII 275.368 in those regions and find no sign of the recurrent outward propagating disturbances with velocities of 40-130km s-1 seen in Fe XII. We do observe downward trends (15-20km s-1) consistent with the characteristic redshifts measured at their footpoints. We, therefore, find no evidence that the structures at these two temperatures and the intensity fluctuations they exhibit are related to one another. © 2011. The American Astronomical Society. All rights reserved.