This paper presents results of studies in atmospheric ultrasonics in unforested areas in the tropics and in the temperate zone. Data of practical interest in regard to the possibilities of ultrasonic signaling were obtained. Fundamental ultrasonic phenomena of propagation were investigated and their causes isolated through correlations with simultaneously observed micrometeorological phenomena. It was found that at times the open air is a scattering, as well as absorbing, medium. Values of absorption coefficients are presented for frequencies up to 30 kc.