Physical mechanisms associated with long range propagation of signals from ionospheric heaters

Summary form only given. Long range (hundreds and thousands km) propagation of heater-produced signals has been studied in experiments with EISCAT and HAARP ionospheric heating facilities (A. V. Zalizovski et al., Radio Sci., 44, RS3010, 1-12, 2009; V. G. Galushko et al., Antennas Prop. Mag., IEEE, 50, 155-161, 2008) and with several globally distributed receiving sites. Two different modes of propagation can be distinguished in the signals spectra. The first one is the regular multihop ionospheric propagation of HF waves radiated by the side lobes of the heater´s antenna array. A distinctive feature of the second component is strong variations in the Doppler frequency shift, which in most cases were synchronous at the different receiving sites. This effect is most likely produced by dynamic effects at the ionospheric altitudes within the main beam of the heater.