TITLE: Atmospheric Gravity Waves and Their Ducting in the Mesosphere and Lower Thermosphere

SPEAKER: Professor Michael P. Hickey,

TIME: Thursday Nov. 8, 2001 at 4 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

In this colloquium I will provide a brief description of the structure of the atmosphere followed by an introduction to atmospheric gravity waves. The importance of these waves to the winds of the mesosphere and lower thermosphere region will be discussed . In particular, their role in the large-scale circulation from summer to winter with consequences for the seasonal variation of the mean temperature will also be elucidated. In this respect, it will be shown that gravity waves can be considered the motor of a global-scale refrigerator. The principles of gravity wave ducting in the mesosphere/lower thermosphere region will be introduced, and a full-wave model capable of simulating this ducting will be described. Observations showing preferred directions of gravity wave propagation will be presented, and model results supporting the claim that these are ducted gravity waves will be discussed. The claim that airglow observations may allow ducted waves to be discriminated from freely propagating waves will be addressed using our model, and shown to be useful for only the highest frequency, fastest gravity waves.