Upper atmospheric waves, turbulence, and winds: Importance for mesospheric and thermospheric studies

U.S. scientists interested in the physics and chemistry of the upper atmosphere (i.e., that region above the Earth's stratosphere, encompassing the mesosphere [∼50–100km], the mesopause region [∼85–100 km], the lower thermosphere [∼100–180km], and the upper thermosphere [∼180–1000km]) have increasingly come to recognize the importance of atmospheric waves of all types. Gravity/buoyancy waves, planetary waves, and tides pervade the upper atmosphere and are, in fact, ubiquitous features of all planetary atmospheres. Upper atmospheric waves generated by dynamical processes propagate vertically and horizontally, dissipate, interact nonlinearly, and profoundly influence the flows of momentum, energy, and constituents on a global basis. These waves also pass vertically through the various regions or “spheres” (troposphere, stratosphere, etc.) of the atmosphere and, in so doing, impel scientists in previously compartmentalized subdisciplines to assess the effects of the processes that couple these regions. For example, tropospheric gravity waves generated by air flow over topographic features can propagate vertically through the stratosphere and dissipate within the mesosphere [e.g., Fritts, 1994]. These “breaking” waves alter the global thermal and wind structures, producing a large mesopause temperature anomaly (cold summer pole, warm winter pole). The mesopause turbulence generated by breaking gravity waves on Earth is substantial and has been noted by astronauts during the gentle buffeting of the reentering Space Shuttle [A. England, private communication, 1994].