A new method of hodograph analysis is introduced and applied to studies of long period wind oscillations (2 to 10-hour period) in the upper mesosphere, observed by a triangle of medium frequency radars (500 km spacing) in the Canadian Prairies. This is compared with a method of spatial Fourier analysis which is also employed to study these oscillations. The results of these analyses are shown to be consistent with the behavior of atmospheric gravity waves: in particular, the gravity wave propagation directions are found to vary with season and with latitude. However, the directions do not seem to be consistent with blocking by the mean wind field, probably due to the gravity waves having phase velocities much higher than typical mean winds. ¿ American Geophysical Union 1995