Traveling ionospheric disturbances near London, Canada

Observations of medium scale traveling ionospheric disturbances (TIDs) from near London, Canada (43°N, 81°W geographic) using spaced transmitter technique at 4 MHz have been done for 112 years. Most of the best data are for daytime TIDs because of the use of 4 MHz. Using this data set we have derived properties of the TIDs such as the speed, direction of propagation and their diurnal, seasonal, and annual variations. Speeds and directions show similar diurnal variations during all months. Typical daytime speeds are of the order of 160 m/s and nighttime speeds are of the order of 300 m/s. Daytime directions are approximately eastward in morning hours and gradually rotate clockwise to approximately southward in late afternoon. Parameters of the TIDs are consistent with two possible sources: upward propagated and filtered mesospheric gravity waves, and/or the sunrise terminator.