Friday, 12 June 2009: 9:00 AM
Pinnacle A (Stoweflake Resort and Confernce Center)
We use the NOGAPS-ALPHA GCM to investigate the effects of longitudinal variations in stratospheric ozone (LVSO) on the circulation of the middle atmosphere. The NOGAPS-ALPHA model extends from the surface to 100 km and combines an operational weather forecast model with an interactive middle atmosphere component that contains parameterized ozone photochemistry. We isolate the effects of LVSO by comparing model simulations using 3-D versus 2-D prognostic ozone heating fields. The simulations are performed for Northern Hemisphere (NH) winter, comparing the results for December, January and February. First results show that the effects of LVSO on the NH December zonal-mean circulation is relatively small and confined to a narrow latitude belt centered in the upper stratosphere-lower mesosphere. The effects of LVSO on the January NH zonal-mean circulation are dramatic. The LVSO cause the 2-D jet core to descend from ~80 km to ~65 km, the maximum wind speed to increase from ~40 m/s to ~ 60 m/s, and the jet half-width to narrow by about ~3º latitude. The effects of LVSO on the NH zonal-mean circulation during February are greater than December but less than January. To explain these model results, an ozone-modified refractive index (OMRI) is used to diagnose the differences between the 3-D and 2-D ozone simulations for each winter month. The OMRI, which explicitly accounts for the longitudinal variations in ozone heating produced by the planetary wave field, is used to distinguish between ozone transport and photochemically accelerated cooling in altering the planetary wave drag and, correspondingly, the zonal-mean circulation. Additional diagnostic calculations involving EP flux divergence, residual meridional and vertical velocities, and refractive indices show how the LVSO affects the model circulation throughout the NH stratosphere and troposphere. The role that LVSO plays in communicating human-caused and naturally-generated perturbations in troposphere-stratosphere coupled system is discussed.
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