Figure 4

Measured power spectra. Measured power spectra of velocities’ fluctuations along the magnetic field line at an altitude of 150 km are compared with predicted contributions due to atmospheric waves radiated by infragravity waves in the ocean. The spectra are measured by radio sounding of the ionosphere using an onshore Dynasonde (Wright and Pitteway 1999; Zabotin et al. 2006) HF radar system located at NASA’s Wallops Island Flight Facility, Virginia, USA. The five panels refer to five distinct seasons in 2013 to 2014, and each panel contains four experimental spectral estimates obtained from the data series, specific dates and times of which are listed in the text. Blue dots show the results of spectral measurements. Red curves represent the results of smoothing the experimental spectra using a 0.5-mHz sliding window. Black curves show contributions of the atmospheric waves of oceanic origin, which are estimated for various ocean depths (200, 1,000, and 5,000 m, top to bottom) using a semi-empirical model (Godin et al. 2013) of the IGW spectra.