Pulse trains with periods of the order of a minute occur in the natural VLF signals emitted in the exosphere. Composed of otherwise ordinary VLF emissions, the long‐period pulses always rise in frequency. At magnetically conjugate points the long‐period pulse signals are received simultaneously. The period of the pulsation events exhibits a latitude dependence, becoming longer at higher latitudes. On the basis of available data, a hypothesis associating hydromagnetic waves with emitting particles is offered to account for the observed properties of the pulsations.

An ins trument, developed at NBS, has enabled continuous observations of VLF e mi ss ions. The continuous data has permitted the identifi cation of some new characteristics of VLF emissions, and new information on the statistics of the occurre nce of VLF e mission activity. The contin uous recordings are able to document the morphology of VLF emiss ion events and, therefor e, acc ura tc correlations with other geophysical phenom ena are possible. Co rrelations of VLF em ission activity with abno rm al D-reg ion absorption, X-ra y events, and magnetic a ctiv ity are prcsented.

B S<2 pi z c s c g-p g4 > °°.