Thermospheric Dynamics during September 18-19, 1984. 2. Validation of the NCAR Thermospheric General Circulation Model

The validation of complex nonlinear numerical models such as the thermospheric general circulation model (NCAR TGCM) requires a detailed comparison of model predictions with data. The Equinox Transition Study (ETS) of September 17-24, 1984, provided a unique opportunity to address the verification of the NCAR TGCM, since unusually large quantities of high-quality thermospheric and ionospheric data were obtained during an intensive observation interval. A quantitative statistical comparison of the predicted and measured winds indicates that the equatorward winds in the model are weaker than the observed winds, particularly during storm times. This is consistent with predicted latitudinal temperature gradients and storm time density increases which are much smaller than the observed values. Soft particle precipitation or high- altitude plasma heating is invoked as a possible source of the additional high- latitude heating required by the model. A quiet day phase anomaly in the measured F region winds which is not reproduced by the model suggests the occurrence of an important unmodeled interaction between upward propagating semidiurnal tides and high-latitude effects. Wind data from altitudes below 100 km indicate shortcomings in the generic equinox solar minimum tidal specification used in the TGCM. The lack of appropriate data to specify input fields seriously impairs our ability to generate realistic global thermospheric simulations. The problem is particularly acute in the southern hemisphere. Reprints. Pub. in Jnl. of Geophysical Research, v94 nA12 p16,945-16, 959, 1 Dec 1989. See also Part 1, ADA221495.