  Recent spectroscopic observations have revealed the ubiquitous presence of
blueward asymmetries of emission lines formed in the solar corona and
transition region. These asymmetries are most prominent in loop footpoint
regions, where a clear correlation of the asymmetry with the Doppler shift and
line width determined from the single Gaussian fit is found. Such asymmetries
suggest at least two emission components: a primary component accounting for
the background emission and a secondary component associated with high-speed
upflows. The latter has been proposed to play a vital role in the coronal
heating process and there is no agreement on its properties. Here we slightly
modify the initially developed technique of Red-Blue (RB) asymmetry analysis
and apply it to both artificial spectra and spectra observed by the EUV Imaging
Spectrometer onboard Hinode, and demonstrate that the secondary component
usually contributes a few percent of the total emission, has a velocity ranging
from 50 to 150 km s-1 and a Gaussian width comparable to that of the primary
one in loop footpoint regions. The results of the RB asymmetry analysis are
then used to guide a double Gaussian fit and we find that the obtained
properties of the secondary component are generally consistent with those
obtained from the RB asymmetry analysis. Through a comparison of the location,
relative intensity, and velocity distribution of the blueward secondary
component with the properties of the upward propagating disturbances revealed
in simultaneous images from the Atmospheric Imaging Assembly onboard the Solar
Dynamics Observatory, we find a clear association of the secondary component
with the propagating disturbances.
