MF radar observations of terdiurnal tide in the mesosphere and lower thermosphere at Wakkanai [formula omitted], Japan

MF radar observations of winds in the mesosphere and lower thermosphere (MLT) at Wakkanai (45.4° N, 141.7° E) have been significantly contributing to the studies of MLT dynamics. The present paper is an attempt to describe the characteristics of the terdiurnal tide at Wakkanai. We have used the continuous data gathered during the 5-year period 1997–2001. Mainly, the analysis focuses upon the seasonal aspects of the terdiurnal tide characteristics. The observed results have been compared with the results reported at London, Ontario, another station located at a similar midlatitude (43° N) sector. It is observed that the terdiurnal tide is a regular feature in the MLT region. There exists strong day-to-day variability in the terdiurnal tide amplitudes. Short-time variability confirms that the terdiurnal oscillation can have an amplitude comparable to that of the diurnal and semidiurnal tides on occasions. Presence of dominant 8-h oscillation is observed in all seasons. However, a strong seasonal dependence is not observed in their amplitude variations. Amplitudes show slightly larger values in the winter season than the corresponding values in the summer season. The terdiurnal amplitudes at Wakkanai are more comparable to the diurnal tide amplitudes than the semidiurnal values. Comparison of the observed characteristics at Wakkanai and London reveals some similarities as well as differences.