First satellite‐imaging observation of medium‐scale traveling ionospheric disturbances by FORMOSAT‐2/ISUAL

On the night of May 16, 2007, a satellite limb imager of FORMOSAT‐2/ISUAL observed wave‐like structures of the 630‐nm airglow simultaneously with an all‐sky imager deployed at Darwin in Australia. The height of the airglow layer was estimated as 220 km, and the structures were aligned in the northeast‐southwest orientation with a wavelength of ∼300 km and propagated toward the northwest with a phase velocity of ∼100 m s−1, showing typical characteristics of the nighttime medium‐scale traveling ionospheric disturbances (MSTIDs). We conclude that ISUAL for the first time succeeded in observing the airglow layer altitude and airglow structures modulated by MSTID from space. Such a satellite limb airglow imaging could be a new tool to characterize ionospheric irregularities on a global level.