The Evolution of the EM Distribution in the Core of an Active Region

We study the spatial distribution and evolution of the slope of the Emission Measure between 1 and 3~MK in the core active region NOAA~11193, first when it appeared near the central meridian and then again when it re-appeared after a solar rotation. We use observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode, with a new radiometric calibration. We also use observations from the Atmospheric Imaging Assembly (AIA) aboard Solar Dynamics Observatory (SDO). We present the first spatially resolved maps of the EM slope in the 1--3~MK range within the core of the AR using several methods, both approximate and from the Differential Emission Measure (DEM). A significant variation of the slope is found at different spatial locations within the active region. We selected two regions that were not affected too much by any line-of-sight lower temperature emission. We found that the EM had a power law of the form EM~$propto T^{b}$, with b = 4.4$pm0.4$, and 4.6$pm0.4$, during the first and second appearance of the active region, respectively. During the second rotation, line-of-sight effects become more important, although difficult to estimate. We found that the use of the ground calibration for Hinode/EIS and the approximate method to derive the Emission Measure, used in previous publications, produce an underestimation of the slopes. The EM distribution in active region cores is generally found to be consistent with high frequency heating, and stays more or less the same during the evolution of the active region.

Observations of Plasma Upflow in a Warm Loop with Hinode/EIS

A complete understanding of Doppler shift in active region loops can help probe the basic physical mechanism involved into the heating of those loops. Here we present observations of upflows in coronal loops detected in a range of temperature temperatures (log T=5.8 - 6.2). The loop was not discernible above these temperatures. The speed of upflow was strongest at the footpoint and decreased with height. The upflow speed at the footpoint was about 20 km/s in Fe VIII which decreased with temperature being about 13 km/s in Fe X, about 8 km/s in Fe XII and about 4 km/s in FeXIII. To the best of our knowledge this is the first observation providing evidence of upflow of plasma in coronal loop structures at these temperatures. We interpret these observations as evidence of chromospheric evaporation in quasi-static coronal loops.