THREE-DIMENSIONAL CORONAL SLOW MODES: TOWARD THREE-DIMENSIONAL SEISMOLOGY

On 2008 January 10, the twin Solar Terrestrial Relations Observatory A and B spacecraft conducted a high time cadence study of the solar corona with the Extreme-Ultraviolet Imager instruments with the aim of investigating coronal dynamics. Observations of the three-dimensional propagation of waves within active region coronal loops and a measurement of the true coronal slow mode speed are obtained. Intensity oscillations with a period of approximate to 12 minutes are observed to propagate outward from the base of a loop system, consistent with the slow magnetoacoustic mode. A novel analysis technique is applied to measure the wave phase velocity in the observations of the A and B spacecraft. These stereoscopic observations are used to infer the three-dimensional velocity vector of the wave propagation, with an inclination of 37 degrees +/- 6 degrees to the local normal and a magnitude of 132 +/- 9 and 132 +/- 11 km s(-1), giving the first measurement of the true coronal longitudinal slow mode speed, and an inferred temperature of 0.84 +/- 0.12 MK and 0.84 +/- 0.15 MK.