Study of mesosphere lower thermosphere (MLT) mean winds over Yamagawa (31.2°N, 130.6°E) during 1996-1998

The mean motions in the mesosphere and lower thermosphere from 70 to 98 km were observed with the recently installed MF radar at Yamagawa (31.2°N, 130.6°E). We have utilized the continuous wind data collected during the 3‐year period 1996–1998. Seasonal variations of mean winds over the site are constructed and the climatologies are then compared with observations from similar latitudes and the latest empirical model results. The mean zonal circulation in the mesosphere is characterized by a clear annual variation with summer westward (easterly) flow and winter eastward (westerly) flow. The summer westward jet closes at a height in between 80 and 85 km. Southward motion exhibits its dominance at 90–98 km during all times of the year, and at lower heights (70–90 km), southward/northward motions predominate during summer/winter season. The annual mean zonal wind has an eastward motion in the 70–98 km. It maximizes at around 90 km with a strength of 15–17 m/s. The annual mean meridional circulation shows both poleward and equatorward motions. Harmonic analysis of mean zonal winds clearly demonstrates the dominance of annual oscillation over the other periods. Comparison of mean winds over Yamagawa, Japan, and London, Ontario, Canada, demonstrates that the zonal circulation over these two sites has some similar features. Similarly, the results compared for Yamagawa and Urbana show some consistency in mean wind circulation. The paper also presents the results of the comparison of MF radar‐derived winds and the HWM93 model outputs. There is reasonable agreement between the observation and the model values.