Plasma draining and replenishing near a solar active region inferred from cross-correlation between radiation intensity and Doppler shift

Abstract

Using observations from the EUV Imaging Spectrometer (EIS) onboard Hinode, we exam the plasma dynamics around the edge of the active region 10977, possibly associated with the source of nascent slow/intermediate solar wind. The correlation between the temporal profiles of the radiation intensity and Doppler shift for each emission line are analyzed. And three small regions with positive correlations for all the five emission lines are selected for a detailed analysis. In this work, Doppler blue (red) shift is defined as negative (positive). We find that in Region 1, the radiation intensity (Doppler velocity) decreases by about 15% (about 3 km s−1), and logarithmical differential emission measures (lg(DEMs)) reduces by about 0.06–0.10% at all temperatures, called “weak dimming”, during a 30-min interval. In Region 2 and Region 3, however, the radiation intensity (Doppler velocity) increases by about 15% (about 3 km s−1), and lg(DEMs) increases by about 0.06%–0.10% at all temperatures, called “weak brightening”. Such weak dimming (weak brightening) could reflect a slow draining (replenishing) of plasma in the solar wind flux tubes, possibly due to a larger (smaller) outflow flux at high altitude than at low altitude. These suggest that the plasma supply could be intermittent with an alternation of draining and replenishing, for which the underlying physical process is yet unknown, at the source region of slow/intermediate solar wind.