VLF/LF sounding of the lower ionosphere to study the role of atmospheric oscillations in the lithosphere-ionosphere coupling

It is shown that sounding of the lower ionosphere boundary by subiono-spheric signals from powerful VLF/LF transmitters can be a useful tool for the investigation of Planetary Waves (PW) with periods in a range of 2-30 days. A specific spring-time transition in the PW dynamic periodograms is revealed from our analysis of several years data using Tsushima, Japan VLF transmitter (10.2 kHz) along the path with length of about 1000km. Earthquake influence in the periodograms could be sometime recognized as an appearance of specific wavelets. We discuss a possibility of PW transportation from the bottom to the upper atmosphere as modulation of shorter-scale gravity waves (GW) inside the troposphere and subsequent demodulation of the GW at the atmosphere-ionosphere boundary for the explanation of observational results. The existence of modulation due to gravity waves in LF signal amplitude is presented to support the above hypothesis.

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