Abstract
Twelve acoustic grenade experiments were conducted during the period September 1968–February 1969 from Barrow, Alaska (71N). These measurements were intended to monitor the transition in the thermal structure of the mesosphere from the persistent summertime case to the dynamic and highly variable winter-time case. The disturbed features typical of winter appeared in the high mesosphere in September, and at successively lower altitudes until December, at which time the full winter structure had been established. In early January, a warming at the stratopause began a chain of events which eventually would restore the summertime structure and thus complete the cycle.
