University of Crete Island of Crete

Large-scale traveling ionospheric disturbances
observed by GPS receiver networks

T. Tsugawa1, K. Shiokawa2, H. Hayashi2, N. Nishitani2, Y. Otsuka2, T. Ogawa2, J. Lei3, A. Saito4
  1. National Institute of Information and Communications Technology, Koganei, Tokyo, Japan
  2. Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi, Japan
  3. High Altitude Observatory, National Center for Atmospheric Research, Colorado, USA
  4. Department of Geophysics, Graduate School of Science, Kyoto University, Japan

We report recent observations of large-scale traveling ionospheric disturbances (LSTIDs) using GPS receiver networks. LSTIDs generally have horizontal wavelengths of more than 1,000 km and periods of 30-180 min. They are believed to be ionospheric manifestations of the passage of atmospheric gravity waves that are generated at high latitudes by energy input from the magnetosphere. Dense GPS receiver networks in Japan (GEONET: GPS Earth Observation Network System) can provide high-resolution total electron content (TEC) maps that reveal precise spatial structure and temporal evolution of LSTIDs. Time sequences of these TEC maps give reliable wave parameters, such as wavelength, propagation velocity, direction, period, amplitude, and damping rate. Geomagnetic conjugate observations of LSTIDs between the northern and southern hemispheres revealed their non-conjugacy. On December 15, 2006, a prominent northward propagating LSTID has been observed by the GEONET and the SuperDARN Hokkaido HF radar in Japan. Comparison between the observations and the CMIT model simulation indicates that it propagated from the high latitudes of the southern hemisphere into the northern hemisphere over Japan. Statistical study of LSTIDs over Japan revealed that they can be observed even under quiet conditions. These quiet-time LSTIDs are often observed in winter and in the daytime. Their equatorward propagation direction and the seasonal and local-time variations of their occurrence are consistent with those of daytime medium-scale TIDs (MSTIDs) detected with dense and wide TEC maps over North America. The quiet-time LSTIDs and the daytime MSTIDs may be the same ionospheric phenomena.

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