Observations of the quasi-2-day wave in the mesosphere and lower thermosphere over Yamagawa and Wakkanai

[1] Mesospheric/lower thermospheric (MLT) winds observed at Yamagawa (31.2degreesN, 130.6degreesE) and Wakkanai (45.4degreesN, 141.7degreesE), using the spaced-antenna technique, have been analyzed to study features of the quasi-2-day oscillations. We have used 4-5 years (1996-2000) of near-continuous data for the analysis. Our results are consistent with the reports at other midlatitude sites. The analysis reveals that the wave features observed at these two stations are similar. The occurrence of the wave event (probably the same) is seen at both stations during the same days. The wave is found every year with the maximum amplitude in the summer months. The meridional component has larger amplitudes than the zonal component. Comparing the amplitudes at the two stations, we find that the values observed at Yamagawa are larger than those at Wakkanai. The amplitude appears to attain its maximum value at around 90 km at both stations. Substantial year-to-year variations are observed in the 2-day wave amplitude. The average wave period observed at Yamagawa and Wakkanai is approximately 48 hours. The study also explores the dependence of the 2-day wave on the background atmospheric circulation. However, further analysis on wave events is needed to obtain a better understanding of this aspect. The results of the present study are also compared with the earlier meteor radar observations in Kyoto, Japan, and some other midlatitude observations. Further coordinated studies are suggested to investigate horizontal structure and generating mechanism of the 2-day wave.