[A-CG30] Extratropical oceans and atmosphere

[ACG30-06] Effects of mid-latitude SST fronts on the middle atmosphere through upward propagating atmospheric waves

★Invited Papers

*Yoshio Kawatani¹, Hisashi Nakamura², Kaoru Sato³, Shingo Watanabe¹ (1.Japan Agency for Marine-Earth Science and Technology, 2.Research Center for Advanced Science and Technology, The University of Tokyo, 3.Department of Earth and Planetary Science, The University of Tokyo)

Keywords:middle atmosphere

We have investigated the effects of mid-latitude Sea Surface Temperature (SST) fronts on the middle atmosphere by using the high-top T106L168 MIROC AGCM. This model has horizontal and vertical resolutions of ~120km and 550 m, respectively, with model top of ~95 km. Non-orographic gravity wave parameterizations were not included. We have conducted two idealized experiments. One used the SST having realistic meridional gradients with zonally uniformed (control run), and the other did the SST with smoothing the meridional gradients of mid-latitude SST front (no SST front run; NF run), similar to the previous study (Nakamura et al. 2008). The previous numerical experiments indicated that with/without SST front showed several differences, such as precipitation, heat fluxes, baroclinic wave activities in the troposphere, and so on. Here we show by our model experiments that more gravity waves are generated around baroclinic waves in the control run, which propagate into the stratosphere and mesosphere. Wave momentum fluxes associated with gravity waves are larger from the upper troposphere to ~0.03 hPa, and westward forcing due to these waves are much larger in the control run than in the NF run. Gravity waves generated in the NF run has smaller amplitude than the control run, and then are dissipated at higher altitudes. As a results, shapes of the zonal mean zonal winds including polar night jets are more realistic in the control run. We would indicate that the SST fronts have impact on not only troposphere but on the middle atmosphere.