Working Group 6: Flows vs. Waves - Does it Matter?

Group Leaders: Ineke De Moortel, Hui Tian

Observations of propagating disturbances (PDs) along coronal structures have been reported by a number of authors since 1999. PDs are present in a large fraction of coronal loops, polar plumes and field lines opened by CMEs. These PDs are mostly interpreted as slow magnetoacoustic waves. However, there has recently been substantial debate within the community as to whether these perturbations are slow magnetoacoustic waves or quasi-periodic upflows. Despite their small amplitude, it has been suggested that they could play a substantial role in the coronal energy and/or mass cycle, solar wind mass supply, and perhaps also additional acceleration of CMEs.

Identifying the true nature of the PDs is essential to clarify their (potential) role as a possible energy transfer mechanism or for coronal seismology purposes. Distinguishing between waves and flows is less straightforward than one might expect. The only distinguishing observational characteristics identified so far are subject to large errors, due to the low signal-to-noise ratio of these small amplitude perturbations (observational data appear to have been pushed to their (current) limits). The waves and flows interpretations can each explain some of the observed properties, but neither can currently account for all of the observational signatures.

The issues this group will focus on include (but are not limited to)

  • What is the root cause of the periodic disturbances (i.e. how are they generated) and what determines their observed speeds and periodicities?
  • Are there other distinguishing signatures/properties of waves and flows apart from the ones proposed in the literature so far? Will we ever be able to discriminate or are both waves and flows present?
  • Why are the propagating disturbances only seen for short distances along coronal structures? If they are waves, what is the relevant damping mechanism? If they are flows, what happens to the material?
  • Are the disturbances in CME-induced dimming regions similar to those in AR boundaries? What role do they play in the recovery of dimming and acceleration of CMEs?