Horizontal velocities and propagation directions of gravity waves in the ionosphere over the Czech Republic

Abstract

Using a five‐point continuous Doppler sounding system operating at 3.59 MHz, developed at the Institute of Atmospheric Physics AS CR (IAP), we investigate propagation directions and velocities of gravity waves (GWs) at altitudes from ∼150 to ∼250 km over the western part of the Czech Republic. The velocities and directions are computed from the time delays between the observations of corresponding GWs at different reflection points that correspond to various sounding paths. We focused on the GWs that produce an S‐shaped trace in Doppler shift spectrograms and are observed close to sunrise and sunset. We have selected about 100 of such events. Our results show that the analyzed GWs propagate with typical horizontal velocities from ∼100 to ∼200 m/s. The north‐south component of GW velocities depends on the season, it is directed northward in the summer and southward in the winter. At the same time, the north‐south component of the neutral winds calculated by the horizontal wind model HWM07 has the opposite sign. Typical observed periods of the analyzed waves range from ∼10 to ∼30 min.