This paper describes a method for obtaining rapid measurements of the phase differences between signals from the ionosphere at two pairs of aerials. Measurements were made, during quiet ionospheric conditions, on the first hop near-vertical reflections using a pulsed 1· 98 MHz radiowave transmitter. Evidence is presented to suggest that a relationship exists between wavelike disturbances of a period of 3 min in the Es layer and pressure oscillations at ground level. From ionosonde records of

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... ionospheric stations around Australia it was found that a large-scale travelling ionospheric disturbance was moving in the F region with a speed of 350 msec-1 towards the south-west. It was overhead at Brisbane at the time the small-scale structure was observed in the E region. Two other cases are also presented to show correlation between Es layer structures and ground pressure oscillations.