High‐frequency radar observations of atmospheric gravity waves in the high‐latitude ionosphere

Abstract

The Johns Hopkins University high‐frequency coherent scatter radar at Goose Bay, Labrador, often observes the effects of propagating atmospheric gravity waves, particularly in ground backscatter returns. To date, these waves have been identified in late fall and early winter on propagation paths directed over the Davis Strait, between northeastern Canada and Greenland. The waves appear as spatially localized enhancements in the backscattered power and as quasiperiodic fluctuations in the backscattered powers, Doppler velocities, and reflection heights. They are generally observed during daylight hours and are usually accompanied by backscatter from higher‐latitude ionospheric irregularities that appear to be located near the ionospheric convection reversal boundary. The lowest frequencies associated with the gravity waves lie in the range 0.4 to 0.6 mHz, and the wavelengths lie in the range 300 to 600 km. The waves generally propagate equatorward at an angle of 150° to 180° east of geographic north. During intervals with an expanded polar cap, northward propagating gravity waves are sometimes observed. Measurements of the parameters of the waves and the ranges to the sources suggest that the waves are excited at a height of 100 to 150 km near the convection reversal boundary and the polar cusp, and that the bulk of the observed perturbations are due to Earth‐reflected waves.