Assessment of the non-hydrostatic effect in general circulation models (GCMs)

Details Assessment of the non-hydrostatic effect in general circulation models (GCMs) Assessment of the non-hydrostatic effect in general circulation models (GCMs)

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa12a..08d&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA12A-08

Physics

0355 Thermosphere: Composition And Chemistry, 3367 Theoretical Modeling, 3369 Thermospheric Dynamics (0358), 3384 Acoustic-Gravity Waves

Scientific paper

Under hydrostatic equilibrium, a typical assumption used in global thermosphere ionosphere models, the pressure gradient in the vertical direction is exactly balanced by the gravity force. Using the Global Ionosphere Thermosphere Model (GITM), which solves the complete vertical momentum equation, the primary characteristics of non-hydrostatic effects on the upper atmosphere are investigated. Our results show that after a sudden intense enhancement of high-latitude Joule heating, the vertical pressure gradient force can locally be 25 percent larger than the gravity force, resulting in a significant disturbance away from hydrostatic equilibrium. This disturbance is transported from the lower altitude source region to high altitudes through an acoustic wave, which has been simulated in a global circulation model for the first time. Due to the conservation of perturbation energy, the magnitude of the vertical wind perturbation increases with altitude and reaches 150 (250) m/s at 300 (430) km during the disturbance. The upward neutral wind lifts the atmosphere and raises the neutral density at high altitudes by a factor of two. While the time scale of the buoyancy acceleration perturbation is around 5-10 minutes in this case, the large vertical wind (above 50 m/s) at 300 km altitude lasts for a significantly longer time, and depends on the lifetime of the forcing. These large vertical winds are observed and are not typically reproduced by hydrostatic models of the thermosphere and ionosphere.

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