Direct Imaging by SDO AIA of Quasi-periodic Fast Propagating Waves of ~2000 km/s in the Low Solar Corona

Abstract: Quasi-periodic, propagating fast mode magnetosonic waves in the corona were difficult to observe in the past due to relatively low instrument cadences. We report here evidence of such waves directly imaged in EUV by the new SDO AIA instrument. In the 2010 August 1 C3.2 flare/CME event, we find arc-shaped wave trains of 1-5% intensity variations (lifetime ~200 s) that emanate near the flare kernel and propagate outward up to ~400 Mm along a funnel of coronal loops. Sinusoidal fits to a typical wave train indicate a phase velocity of 2200 +/- 130 km/s. Similar waves propagating in opposite directions are observed in closed loops between two flare ribbons. In the k-$\omega$ diagram of the Fourier wave power, we find a bright ridge that represents the dispersion relation and can be well fitted with a straight line passing through the origin. This k-$\omega$ ridge shows a broad frequency distribution with indicative power at 5.5, 14.5, and 25.1 mHz. The strongest signal at 5.5 mHz (period 181 s) temporally coincides with quasi-periodic pulsations of the flare, suggesting a common origin. The instantaneous wave energy flux of $(0.1-2.6) \times 10⁷ ergs/cm<sup>2/s$ estimated at the coronal base is comparable to the steady-state heating requirement of active region loops.