Geomagnetic conjugate observation of nighttime medium‐scale and large‐scale traveling ionospheric disturbances: FRONT3 campaign

Abstract

The third FRONT (F‐region Radio and Optical measurement of Nighttime TID) campaign was carried out during the new‐moon period of May–June 2003, in order to investigate the geomagnetic conjugacy of medium‐scale and large‐scale traveling ionospheric disturbances (MSTIDs/LSTIDs) at midlatitudes. Seven all‐sky airglow imagers were operated in Japan and Australia. For almost all clear‐sky nights, we observed MSTIDs in the 630‐nm airglow images with horizontal wavelengths of 100–400 km propagating southwestward in Japan and northwestward in Australia. All of them show a one‐to‐one correspondence of wave structures between the Northern and Southern Hemispheres, indicating strong electrodynamic coupling between the two hemispheres through the geomagnetic field line. We also found that airglow intensity variations with a timescale longer than that of MSTIDs often show a good correlation between the two hemispheres. On 28 May, we succeeded in detecting an equatorward propagating LSTID (spatial scale ∼1000 km) as airglow enhancements at the conjugate stations. The airglow peak of the LSTID in the Northern Hemisphere was ∼20 min earlier than that in the Southern Hemisphere, indicating that the observed LSTID is caused by a wave in the neutral atmosphere rather than by an electric field structure.