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

Propagating Intensity Disturbances in Fan-like Coronal Loops: Flows or Waves?