A RECENT publication1 from this laboratory has discussed the existence of large travelling ionospheric disturbances which during winter daylight hours travel from south to north over the east coast of Australia. This type of disturbance first described by Munro and Heisler2 has been tracked from Hobart to Townsville, a distance of 3,000 km. with no apparent change in amplitude. Moreover, the frontal extent of the phenomenon is at least 1,000 km. and may be greater. Munro3 found evidence in the northern hemisphere ionosonde records of similar disturbances travelling south during the winter months. This has been confirmed by Wells4 and verified at Stanford University in a recent report5 which shows how back-scatter techniques have been used to find many examples of giant travelling ionospheric disturbances, some of which have been shown to extend at least from the east to the west coasts of America and to travel distances of 4,000 km.