Northward-propagating nighttime medium-scale traveling ionospheric disturbances observed with SuperDARN Hokkaido HF radar and GEONET

We report on the characteristics of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) propagatingnorthward observed with the SuperDARN Hokkaido HF radar, which has a field of view to the north of Japan, and occasionallywith the GNSS Earth Observation NETwork (GEONET), which provides total electron content (TEC) data over Japan. From statisticalanalysis of MSTIDs observed with the Hokkaido radar during nighttime (1700–0700 LT) from January 2007 to July 2009, wefind that these MSTIDs traveling northward, although rare in comparison with those traveling southwestward, have a relativelyhigh occurrence rate after sunset and around midnight in May and August, which is partly consistent with the occurrence rate ofMSTIDs over Japan observed with GEONET in 2002, when the MSTID event database is available. We also use the data fromsimultaneous observation of nightside MSTIDs by the Hokkaido radar and GEONET to find that when the HF radar observednorthward-propagating MSTIDs, GEONET did not always observe such MSTIDs with the same propagation direction. Judgingfrom this result and considering the HF radar field of view located to the north of the GEONET coverage area, we speculate thatsome physical parameters of the ionosphere/thermosphere over Japan differ from those to the north of Japan, which may result inthe inconsistency of MSTID propagation direction. The present results provide new knowledge of MSTIDs propagating northwardusing the Hokkaido radar, whose field of view was not covered by GEONET.