| The classical laboratory simulations suggest that the generalcirculation of a rotating fluid is determined both by the rotationrate and by the differential diabatic heating. As these laboratoryexperiments only crudely represent the atmosphere, it is worthwhile tofurther quantify the effect of the two external forcings usingnumerical models. So far numerical experiments have been mainlyfocused on the role of the earth´s rotation rate. As acomplementation, this paper studies the impact of the latitudinalheating from the sun on the general circulation. A ′dry′ atmosphericGCM is used for this purpose. The diabatic forcing is parameterizedby a Newtonian forcing. With this parameterization, the strength ofthe net latitudinal differential heating is controlled by thepole-to-equator difference in the restoring temperature, DT. To studythe effect of differential thermal forcing on the general circulation,the model is integrated using different DT.It is found that an increase in the differential heating leads tostrengthen the general circulation. The strengthening is characterizedby regimes with different types of mean-flow eddy interactions. Forextremely weak differential heating, the general circulation isdescribed by a Hadley circulation with no eddy activity. As thedifferential heating increases, an indirect circulation in conjunctionwith large-scale waves emerges at the mid-latitudes and a weak polarcell appears in the polar region. The most pronounced waves aresynoptic ones, and have wave number 6 and 7. As the differentialheating further increases, the indirect circulation increases both instrength and size and covers the entire mid-latitude and polarregion. This change is accompanied by a change in waves. The waveshave now larger spatial scales with the dominant wave number being 3.The changes in the general circulation and the mean-flow eddy regimescan be summarized from an energetic point of view. The increase indifferential heating leads to an increase in available potentialenergy, which is then transferred into the mean kinetic energy(i.e. the energy of the mean circulation). As long as the meancirculation is weak and stable, as generated by a weak differentialthermal forcing, the available potential energy generated by thedifferential forcing will be entirely used to generate and maintainthe mean circulation. Once the mean circulation becomes unstable, theavailable potential energy will also be used to ′feed′ the eddies. Inthis sense, the different mean-flow eddy regimes represent differentways of a fluid to adapt to an increase in available potential energy. |
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