An attempt to detect atmospheric free oscillations by a new array deployment of micro-barometers

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Network Construction(1) We replaced a 10 MHz clock of our micro-barometer system with a 50 MHz clock to increase resolution especially on a higher frequency side. We also developed a telemeter data-transmission system which enabled us to retrieve network data by PC at hand.(2) We installed the system at each of 14 stations of our network in the Kanto-Tokai districts. , which is now in routine operation. The amount of the data now available is not as large as originally anticipated because of the compelling change of the system design.(3) We examined the noise spectrum of air pressure fluctuation at each station and found a strange behavior of aero-acoustic tremor. We detected aero-gravity waves at 1-5mHz propagating from the west to east at a speed of 60 m/s.(4) We summarized the observational results obtained by the beginning of 2007, which were reported at an international conference in Greece.Results from Data Analyses and Theoretical Analyses(1) We developed an excitation model that can explain the observed resonance phenomenon of free oscillations between the solid Earth and the atmosphere, based on which we estimated the pressure amplitudes of atmospheric free oscillations to show that the detection is feasible.(2) We analyzed the IRIS seismograms to show that the excitation source of background free oscillations lies in the Pacific. The source moves seasonally. The sources are not limited to shallow seas but should extend to abyssal planes.(3) We detected background Love waves from tiltmeter network data in Japan. Kinetic energy ratio of Love to Rayleigh waves is approximately one. The background waves are strongest from ocean-continent borders, next from abyssal planes and weakest from continents.(4) We developed an excitation model attributing background Love and Rayleigh waves to topographic coupling of infragravity waves that effectively generates tangential stress acting on the presumed seafloor horizon.