The stratopause semiannual oscillation in the NCAR Community Climate Model. [NCAR (National Center for Atmospheric Research)]
- National Center for Atmospheric Research, Boulder, CO (United States)
The middle atmospheric version of the NCAR Community Climate Model (CCM2) has been used to study development of the equatorial semiannual oscillation (SAO) in the stratosphere. The model domain extends from the ground to about 80 km, with a vertical resolution of 1 km. Transport of nitrous oxide (N[sub 2]O) with simplified photochemistry is included in the calculation to illustrate the influence of tropical circulations on the distribution of trace species. Diagnosis of model output reveals two distinct phases in the evolution of the zonal mean state on the equator. In December, a strong and broad easterly jet appears near the stratopause in connection with a midlatitude wave event that reverses the winter westerlies of the Northern Hemisphere throughout the upper stratosphere. When the wave forcing dies out, the radiative drive allows the westerlies to recover at midlatitudes, while easterlies persist in the tropics. The resulting strong meridional gradient of the zonal mean wind provides favorable conditions for the development of inertial instability at lower latitudes. In equinoctial conditions, a jet of westerlies appears in the lower equatorial mesosphere and descends to lower altitudes. The descent of the westerly jet does not reproduce well the observed behavior of the SAO westerly phase, either in amplitude or in the extent of downward propagation. The model does not simulate the [open quotes]double peak[close quotes] observed in the tropical distribution of N[sub 2]O. Comparison of wave amplitudes in the model with those derived from satellite observations shows the calculated amplitudes are larger than observed in the upper stratosphere. It follows that inadequate Kelvin wave forcing is not the cause of the weak westerly phase, and that some other mechanism must be responsible for generation of the strong westerly phase observed. 54 refs., 40 figs.
- OSTI ID:
- 5582674
- Journal Information:
- Journal of the Atmospheric Sciences; (United States), Vol. 50:21; ISSN 0022-4928
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
EARTH PLANET
CLIMATE MODELS
NITROUS OXIDE
ATMOSPHERIC CHEMISTRY
STRATOSPHERE
ATMOSPHERIC CIRCULATION
COMPUTERIZED SIMULATION
EQUATOR
MESOSPHERE
METEOROLOGY
NORTHERN HEMISPHERE
OSCILLATIONS
PHOTOCHEMISTRY
TEMPERATURE DISTRIBUTION
WAVE PROPAGATION
WIND
CHALCOGENIDES
CHEMISTRY
EARTH ATMOSPHERE
MATHEMATICAL MODELS
NITROGEN COMPOUNDS
NITROGEN OXIDES
OXIDES
OXYGEN COMPOUNDS
PLANETS
SIMULATION
540120* - Environment
Atmospheric- Chemicals Monitoring & Transport- (1990-)
540110