Earth–ionosphere waveguide Earth and the ionosphere. The round-the-world nature of the waveguide produces resonances, like a cavity, which are at ~7 Hz. Radio propagation within the ionosphere depends on frequency, angle of incidence, time of day, season, Earth's magnetic field, and solar activity. At vertical incidence, waves with frequencies larger than the electron plasma frequency (f) of the F-layer maximum (1) f = 9 (N) kHz (N in cm is the electron density) can propagate through the ionosphere nearly undisturbed. Waves with frequencies smaller than f are reflected within the ionospheric D-, E-, and F-layers. f is of the order of 8–15
Rough Waves Shukei (), whose still-extant paintings include a number of dynamic and mysterious images of sea waves, among them "Egret, Moon, and Wave" and "The Wind and the Waves". "Rough Waves" also reflects the influence of Tawaraya Sōtatsu, who specialized in gloomy landscapes, but is nevertheless an independent interpretation by Ogata of the frightening and violent force of the sea. "Rough Waves" impressed Ogata’s follower Sakai Hōitsu, who in 1805 created his work "Waves", in which he tried to convey a similar frightening atmosphere and a premonition of danger. At some time in the past, Hōitsu's family had commissioned work from