VLF monitoring of atmosphere-ionosphere boundary as a tool to study planetary waves evolution and seismic influence

It is shown that sounding of the lower ionosphere boundary by subionospheric signals from powerful VLF transmitters can be a useful tool for investigation of the 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 the analysis of several years data using Tsushima, Japan VLF transmitter (10.2 kHz) along the path with length of about 1000 km. 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 explanation of the observational results. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.