A Complication to the "Coronal Seismology" Paradigm

Wednesday, December 1, 2010

Quasi-periodic propagating disturbances are frequently observed in coronal intensity image sequences. These disturbances have historically been interpreted as being the signature of slow-mode magnetoacoustic waves propagating into the corona from the lower atmosphere and have been a strong driving influence of "Coronal Sesimology". Coronal Seismology uses the observed properties of the observed magnetohydrodynamic waves as probe of the physical properties (temperature, density, magnetic field, etc) of the solar atmosphere.

De Pontieu & McIntosh (2010) and Tian, McIntosh & De Pontieu (2010) provided detailed analysis of Hinode EUV Imaging Spectrometer (EIS) timeseries observations of an active region shows strongly correlated, quasi-periodic, oscillations in intensity, Doppler shift, and line width. The enhancements in these "moments" of the line profile are generally accompanied by a faint, quasi-periodically occurring, excess emission at ~100 km/s in blue wing of the several high signal-to-noise coronal emission lines. These quasi-periodic upflows have been identified with high velocity mass flows triggered in the lower solar atmosphere and can be directly identified in simultaneous image sequences obtained by the Hinode X-Ray Telescope (XRT) as well as broadband imagers on the Solar Dynamics Observatory and STEREO spacecraft.

The results of these papers appear to push the growing debate of "waves vs flows" in favor of the latter, as such correspondences are hard to reconcile in the wave paradigm although it should be noted that the insertion of a mass "plug" from the lower atmosphere will undoubtedly trigger the propagation of a wave through the corona. Future work will investigate the prevalence of one flavor of disturbance over the other and the balance between the two.