Goose Bay radar observations of Earth‐reflected, atmospheric gravity waves in the high‐latitude ionosphere

Abstract

In the late fall and early winter, The Johns Hopkins University HF radar at Goose Bay, Labrador, observes the effects of atmospheric gravity waves on radar transmissions that are obliquely reflected from the ionosphere and subsequently backscattered from the Earth's surface. The waves exist under a wide variety of geomagnetic conditions; how ever, they are particularly noticeable under quiet conditions (0 ≤ Kp ≤ 1 +). The clearest signatures of the waves are spatially localized enhancements in the backscattered power and quasi‐periodic fluctuations in the backscattered powers, Doppler velocities, and reflection heights. The waves are generally observed during daylight hours and propagate equatorward from regions of high‐latitude ionospheric backscatter that are located near the ionospheric convection reversal boundary. The gravity waves appear to be generated just equatorward of the dayside flow‐reversal boundary in the vicinity of the auroral electrojet at altitudes of 115 to 135 km and propagate approximately perpendicular to the boundary along azimuths ranging from 156° to 180°. The waves propagate obliquely downward through the lower atmosphere until they are reflected by the Earth's surface back into the upper atmosphere. The frequencies associated with these gravity waves cover the range of 0.3 to 0.6 mHz, with wavelengths of 300 to 500 km, and with average phase velocities of 110 to 180 m/s. The maximum phase speeds are 270 to 300 m/s, which is slightly less than the speed of sound in the lower atmosphere. Poleward‐propagating gravity waves are sometimes observed under disturbed conditions when the polar cap and convection reversal boundary have expanded equatorward.