First SDO/AIA Observations of Global Coronal EUV "Waves": Multiple Components and "Ripples"

Details First SDO/AIA Observations of Global Coronal EUV "Waves": Multiple Components and "Ripples" First SDO/AIA Observations of Global Coronal EUV "Waves": Multiple Components and "Ripples"

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh13a..07l&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SH13A-07

Astronomy and Astrophysics

Astrophysics

[7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7513] Solar Physics, Astrophysics, And Astronomy / Coronal Mass Ejections, [7549] Solar Physics, Astrophysics, And Astronomy / Ultraviolet Emissions

Scientific paper

Global coronal EUV disturbances (so-called "EIT waves") are useful diagnostics for physical conditions on the Sun. Major drawbacks that hindered our understanding of this phenomenon were previous instruments' single view point, low cadence (e.g., 12 minutes of EIT), and limited wavelength coverage. The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) observes the full-sun corona at 10 EUV and UV wavelengths, covering a wide range of temperatures, with high resolution (1.4") and cadence (up to 12 s). It thus offers a great chance to end the decade long debate on the nature of global EUV "waves". We present here the first AIA observations of such phenomenon on 2010 April 8 revealed in unprecedented detail and discuss their physical implications. The disturbance exhibits two components: one weak, diffuse pulse superimposed by multiple strong, sharp fronts, which again have slow and fast components. The disturbance originates in front of erupting coronal loops and the slow sharp front undergoes acceleration, both implying the disturbance being driven by the coronal mass ejection (CME). Even at a 20 s cadence, the diffuse pulse propagates at a surprisingly constant velocity of ~200 km/s, weakly dependent on direction. The fast sharp front overtakes the slow front, producing multiple "ripples" and steepening of the local pulse, and both fronts propagate independently afterwards. These resemble the nature of real waves. Unexpectedly, the amplitude and FWHM of the diffuse pulse decreases linearly with distance. The diffuse pulse appears as emission enhancement at hotter 193 Å but reduction at cooler 171 Å, suggestive of heating, while the sharp fronts appear as enhancement at both wavelengths, indicating density increase. As evidence for both wave and non-wave models of "EIT waves" has been found, we suggest that a hybrid model combining both mechanisms (e.g., Cohen et al. 2010) may best explaine the data. In addition to the global EUV disturbance, we found fast (600-1100 km/s) features repeated at 100 s intervals as tentative evidence of fast mode MHD waves. Discoveries of the fast features, multiple ripples, and two-component fronts were made possible for the first time thanks to AIA's high cadences and sensitivities.

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