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Abstract:
Effects of mid-latitude Sea Surface Temperature (SST) fronts on the middle atmosphere were investigated by using the high-top 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 with realistic meridional gradients (control run), and the other did the SST with smoothing meridional gradients of mid-latitude SST front (no SST front run; NF run), similar to the previous study (e.g., Nakamura et al. 2008). Previous numerical experiments showed that mid-latitude SST fronts affect precipitation, heat fluxes, and baroclinic wave activities in the troposphere. Our model experiments further showed that more gravity waves were generated around baroclinic waves in the control run than the NF run, which propagate into the stratosphere and mesosphere. Wave momentum fluxes associated with these gravity waves are larger from the upper troposphere to ~0.03 hPa, resulting in larger westward forcing in the control run. Amplitudes of gravity waves in the NF run were smaller than those in the control run, and these waves tend to be dissipated at higher altitudes. Shapes of the zonal mean zonal winds including polar night jets are more realistic in the control run, indicating the SST fronts have impact on not only the troposphere but also on the middle atmosphere.
