The spatial distribution features of three Alpha transmitter signals at the topside ionosphere

The spatial distribution features of electric field over three Alpha transmitters in Russia were analyzed based on the Demeter satellite records at local nighttime during the solar minimum in December of 2008, where the three transmitters are with the same emitted power of 500 kW and the same radio waves at 11.9 kHz, 12.6 kHz, and 14.9 kHz. The results of observations showed that the maximal electric field reached −80 to −70 dB (hereafter referred as to V/m) at 660 km altitude, and the horizontal covered area even exceeded 80° in longitude with electric field above −100 dB at 14.9 kHz. The lowest electric field and the smallest longitude scale were detected over Krasnodar (KRA), which is demonstrated that the lower ionosphere plays an important role in attenuating the energy as suggested by the simulation results from the full‐wave propagation model. Another feature over KRA was the significant decrease in electromagnetic field strength at 11.9 kHz and 12.6 kHz, being one order of magnitude lower than the other two transmitters, where the lower hybrid resonance waves affected severely the whistler mode wave mode propagation. Compared with the ground very low frequency observations at Tonghai and Ya'an in China, the most complex variations were observed from KRA, while the east transmitter Khabarovsk maintained high strength of electromagnetic power in a longer distance than the middle transmitter Novosibirsk in local nighttime, which is consistent with the large covering scale in the topside ionosphere due to the enhancement by wave‐particle interaction from the other transmitter. Key Points The electric field can reach −80 to −70 dB (V/m) with the emitted power being 500 kW in solar minimum winter season in local nighttime The big decrease at 11.9 kHz and 12.6 kHz over KRA was related to the higher electron density and LHR frequency in the lower ionosphere The large‐scale strong electromagnetic intensity over KHA was verified by satellite and ground measurements possibly from NWC