Global study of northern hemisphere quasi-2-day wave events in recent summers near 90 km altitude

We attempt to find the northern hemisphere zonal wavenumber for a striking quasi-2-day wave “event” or “burst” observed near 90 km altitude in the summer of 1992. A unique set of data on the upper atmosphere from nine radar sites is analysed (spacings ∼400– ∼ 12,000 km), and compared with expectations from models. The 2-day wave phase comparison, which finds zonal wavenumber m = 4, is conclusive. Determination of n, which defines the meridional wave amplitude structure, is not attempted, as the sites here have only a small latitude spread (21°N to 55°N). Also the amplitude seems to be unstable showing some sort of modulation which is not simultaneous at all sites. Finally, the radars have not been “calibrated” against each other in terms of wind speed. This calibration would have to be done before small differences in wave amplitude could be believed. A similar event in 1991 for which fewer sites are available is also discussed. Here the choice between m = 3 and 4 is not as clear.