Correlation of Winds and Geographic Features with Production of Certain Infrasonic Signals in the Atmosphere

Summary Of the waves which propagate in the atmosphere at acoustic velocity in the period range from 10 to 100 s, one type has been classified by triangulation as arising principally from mountainous regions. These signals were first described as 'northwesters' or '310 ers' by the NBS Geoacoustics Group under R. K. Cook at Washington, D.C., from the predominant direction of arrival. Subsequent operation of an observatory at Boulder, Colorado by Vernon Goerke gave a source region by triangulation in the Pacific Northwest, primarily in Montana and Alberta. Installations of observatories at College, Alaska (Wilson) and Pullman, Washington-Moscow, Idaho (Craine and Thomas) enlarged the data base available, and triangulation showed the principal source areas to be along the coast of British Columbia and in the inland Rocky Mountains of the British Columbia-Alberta border. This paper discusses the presently known characteristics of this class of infrasonic waves, locates the triangulation areas, reviews selected events, and suggests that certain of these waves are produced as aerodynamic sound. The paper shows a correlation between the 500 mb jet stream velocity and direction in these mountainous regions, and the detection of these atmospheric pressure waves.