A 6.5-DAY WESTWARD PROPAGATING PLANETARY WAVE - ORIGIN AND CHARACTERISTICS

A large (10-30 m s(-1)) 6-7 day period westward propagating planetary wave was seen in both ground radar and satellite data within the 80-10 0 km height regime during August and September 1993. Previous analyses of these data argue that it was most likely a manifestation of the (1 ,-2) Rossby planetary wave commonly referred to as the 5-day wave, per haps shifted to longer periods by interaction with the mean zonal wind s. Ln this study the global scale wave model (GSWM [Hagan et al., 1993 ]) is used to analyze the characteristics of this westward propagating wave. We propose that the observed wave is not a Doppler-shifted 5-da y wave but rather an unstable mode, drawing energy from unstable regio ns in the upper mesosphere, whose realization is global in scale. The concept of atmospheric instability is used to determine a likely sourc e region, and the model is used determine the characteristic period, g rowth rate, and perturbation fields of the instability-driven wave.