  Quasi-periodic intensity disturbances propagating upward along the coronal
structure have been extensively studied using EUV imaging observations from
SOHO/EIT and TRACE. They were interpreted as either slow mode magnetoacoustic
waves or intermittent upflows. In this study we aim at demonstrating that time
series of spectroscopic observations are critical to solve this puzzle.
Propagating intensity and Doppler shift disturbances in fanlike coronal loops
are analyzed in multiple wavelengths using the sit-and-stare observations from
Hinode/EIS. We find that the disturbances did not cause the blue-wing asymmetry
of spectral profiles in the warm (~1.5 MK) coronal lines. The estimated small
line-of-sight velocities also did not support the intermittent upflow
interpretation. In the hot (~2 MK) coronal lines the disturbances did cause the
blue-wing asymmetry, but the double fits revealed that a high-velocity minor
component is steady and persistent, while the propagating intensity and Doppler
shift disturbances are mainly due to variations of the core component,
therefore, supporting the slow wave interpretation. However, the cause for
blueward line asymmetries remains unclear.
