We use a simple GCM to investigate two aspects of the general circulation of the atmosphere. First, we investigate the effects of zonal jet structure on the leading mode of variability in the Northern Hemisphere. Model results reveal that the leading mode of variability is dependent on the distance between the eddy-driven and subtropical jets. These results provide a possible explanation for the reduced amplitude of the Northern Annular Mode in the Pacific sector relative to that in the Atlantic sector. Second, we explore the response of the Brewer-Dobson circulation to warming of the tropical troposphere that is qualitatively consistent with the warming typically associated with a doubled CO2 environment in climate models. The strength of the modeled Brewer-Dobson circulation increases in response to the tropospheric tropical warming. A simple dynamical mechanism is found that forces the observed increase in the strength of the circulation. The tropical warming causes the baroclinicity to increase in mid-latitudes, which leads to increased wave activity. Increased wave propagation from the troposphere results in stronger EP flux convergence in the stratosphere that drives a stronger Brewer-Dobson circulation.
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