  Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily at Sun
center from the end of 2006 to early 2011, we studied the long-term evolution
of the quiet corona. The light curves of the higher temperature emission lines
exhibit larger variations in sync with the solar activity cycle while the
cooler lines show reduced modulation. Our study shows that the high temperature
component of the corona changes in quiet regions, even though the coronal
electron density remains almost constant there. The results suggest that heat
input to the quiet corona varies with the solar activity cycle.
