Preliminary Results of Auroral Dynamics Observed by the ATV-VIS Imager aboard EXOS-D (AKEBONO)

The visible (Oxygen green line: 557.7 nm) TV camera aboard EXOS-D (Akebono) takes successive auroral images every 8 sec, which are characterized as a snapshot image of a wide area with high spatial and temporal resolutions. The followings are some preliminary results, when the satellite was located at altitudes of 3000 to 4700 km in the southern hemisphere. (1) At the magnetospheric disturbances, the faint enhanced aurora (MLT width less than about 0.2 hours ≈3°) along the meridian at the pre-midnight was formed, extending from 74° CGL down to 65° CGL. The brightening of the spot was first activated at the higher latitude with subsequent propagation/elongation to the lower latitude. (2) During the storm recovery phase the brightening was confined to a small region (MLT width being less than 0.2 hours or about 330 km across in the ionosphere) of discrete aurora in the high latitude side of the midnight auroral oval. Newly intensified auroral arcs along the pre-existing faint discrete aurora were successively coming out to the westwards. (3) The discrete auroral arc showed a clockwise rotation viewed in the direction of the geomagnetic field. (4) Interestingly, a 557.7 nm airglow layer was observed whenever the field of view covered the earth's limb.