Line Profile Asymmetries, Densities, Spicules, and Nanoflares

EUV spectral line profiles from hot plasmas often have a subtle asymmetry. Enhancements in the blue wing are indicative of fast upflows, perhaps associated with the hot tips of type II spicules and perhaps associated with chromospheric evaporation due to coronal nanoflares. Klimchuk (2012, JGR) recently discussed three observational tests of the hypothesis that spicules provide most of the hot plasma observed in the corona. He found that the hypothesis fails two of the tests. We here examine the third test, based on conservation of mass, which relates the density of the fast upflow to the density of the slow cooling downflow. We use a pair of density sensitive Fe XIV lines observed by Hinode/EIS to measure the densities of the excess blue wing emission and of the line core. The densities are comparable. This is consistent with what is expected for coronal nanoflares, but far different from what is expected for spicules. If spicules provided most of the hot plasma that exists in the corona, the blue wing density would be approximately two orders of magnitude larger than the core density. We conclude from this and the other two tests that spicules inject only a small amount of hot plasma into the corona. We describe our results and a new iterative method that we have developed to detect subtle features in line profiles, call intensity conserving spline interpolation (ICSI).