Mean winds in the mesopause region observed by MF radars at 31° and 45°N

Mean winds in the mesopause region (78-98 km) were observed in northern (45 degrees N) and southern (31 degrees N) Japan by MF radars. The change of the horizontal wind vector with height is illustrated by means of hodographs for solstices and equinoxes. The observations in southern Japan show a stronger meridional wind than in northern,Japan. At the December solstice 1996 the meridional wind over southern Japan changes from a northward wind of around 15 m/s at 78 km to a southward wind of 10 m/s at 98 km height. At the March-and September equinoxes the southward wind increases from around 0 to 15 m/s in this region. The observed meridional wind is significantly stronger than he meridional wind of the empirical HWM93 wind model, but is in agreement with previous observations by the MU radar in Kyoto (35 degrees N). The temporal behaviour of the mean wind hodographs is shown for the three annual cycles from 1994-1997 over southern Japan. (C) 1998 Elsevier Science Ltd. All rights reserved.