SOME ASPECTS OF THE SENSITIVITY OF STRATOSPHERIC CLIMATE SIMULATION TO MODEL LID HEIGHT

Two ensembles of simulations of the middle atmosphere are compared for early northern hemisphere winter. The two ensembles differ only in th e position of the model lid (80 km or 96 km). Two sets of comparisons are carried out using a primitive equation mechanistic model; the firs t uses Rayleigh friction in the mesosphere to mimic the effect of grav ity waves, and the second uses the Hines gravity wave parameterization . Simulations which use Rayleigh friction are found to show little cli matic sensitivity to the position of the lid. Simulations which use th e Hines parameterization are shown to be very sensitive to the positio n of the lid, and this sensitivity is seen directly up to six scale he ights below the lid. Indirect effects may extend throughout the middle atmosphere. This sensitivity is believed to be due to real circulatio n changes and not any numerical artifacts resulting from reflections f rom the model lid.