Fig. 11
From: Statistical investigation of gravity wave characteristics in the ionosphere
GW characteristics obtained from 2D analysis for the period September 2018–August 2019 (solar minimum). a Apparent horizontal velocities obtained by sounding at 3.59 and/or 4.65 MHz, b azimuth of propagation, c apparent horizontal velocities obtained by sounding at 4.65 MHz only, d azimuth difference ϕ between apparent horizontal velocities and velocities of neutral winds. The values are color–coded. Dashed lines indicate times of sunrise and sunset