Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsa11a..06a&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SA11A-06
Other
0300 Atmospheric Composition And Structure, 1600 Global Change
Scientific paper
The upper atmosphere is strongly linked to the lower atmosphere via a number of dynamical, radiative, kinetic, and other processes. An overview of recent CEDAR modeling results will be presented to demonstrate the importance of these coupling mechanisms for the thermal structure of the mesosphere and lower thermosphere (MLT). The temperature distribution observed in the MLT is characterized by a very cold summer mesopause and a relatively warm winter mesopause at middle and high latitudes. Dissipation and breaking of small-scale gravity waves propagating from sources in the lower atmosphere have long been considered responsible for driving this unusual latitudinal-seasonal temperature distribution. Recently, after the introduction of the Doppler-spread parameterization of gravity waves by Prof. C. O. Hines, it has become possible to produce very realistic simulations that compare well with in-situ and remote temperature observations in the MLT. The observed increases in greenhouse gases related to the global warming in the lower atmosphere should produce a substantial ``greenhouse cooling'' in the upper atmosphere. Increased amounts of CO2, for example, result in a strong in-situ cooling in the MLT. Absorption of a colder infrared radiation emanating from the stratosphere may also contribute to the overall cooling observed in the MLT during the last several decades. Although the direct radiative cooling is no longer important at higher altitudes, the molecular thermal conduction acts to cool down the thermosphere. The strong thermospheric cooling in turn results in the neutral density decreases in agreement with recent analyses of historic satellite-drag data.
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