Open Access

Imaging observations of the equatorward limit of midlatitude traveling ionospheric disturbances

  • K. Shiokawa1,
  • Y. Otsuka1,
  • M. K. Ejiri1,
  • Y. Sahai1,
  • T. Kadota1,
  • C. Ihara1,
  • T. Ogawa1,
  • K. Igarashi2,
  • S. Miyazaki3 and
  • A. Saito4
Earth, Planets and Space201454:BF03352421

Received: 31 October 2000

Accepted: 25 July 2001

Published: 18 June 2014


This paper reports the first attempt to observe the equatorward limit of medium-scale traveling ionospheric disturbances (TIDs) in the middle latitudes. The TIDs usually propagate southwestward in the northern hemisphere. An all-sky cooled-CCD imager measured 630-nm airglow at a southern island of Japan, Okinawa (26.9°N, 128.3°E, geomagnetic latitude (MLAT) = 17.0°), during the FRONT-2 campaign of August 4–15, 1999. The TIDs were detected at the mainland of Japan (21°–36° MLAT) by the total electron content (TEC) observations of more than 1000 GPS receivers. In the August 4 event, the TIDs moving southwestward was seen only in the northern sky of Okinawa as a depletion band in the 630-nm airglow images. In the August 6 event, the TIDs were not seen in the 630-nm images at Okinawa, although weak TID activity was observed by the GPS network at the mainland of Japan. The TEC data also showed weakening of the TID activity below 18° MLAT. Based on these observations, we suggest that there is a possible limit of medium-scale TID propagation around 18° MLAT.