Tuesday, 16 January 2007: 2:00 PM
"Two Worlds" View on the General Circulation of the Atmosphere - From Phillips (1956) to NICAM (2006) and Beyond
217C (Henry B. Gonzalez Convention Center)
Half a century has passed since the first numerical experiment of the general circulation of the atmosphere by Phillips appeared. Since then, global atmosphere models have made great progress and they are successfully applied to numerical weather prediction and climate prediction as well as simulation. The driving force of the atmospheric motions is basically differential heating arising from imbalance of net radiation heating. It is well known that there are two components in differential heating; latitudinal and vertical ones. So far, global atmosphere models have been developed mostly by focusing on simulations of large (synoptic) scale weather systems in the middle-high latitudes such as extratropical cyclones and fronts and so on which are produced by the latitudinal differential heating or baroclinic instability. In the tropics primary energy source for atmospheric motions is static instability caused by the vertical differential heating. The convection to compensate the radiative imbalance takes place as meso-scale convective systems consisting from cumulonimbi and they are elementary components for producing various weather and circulation systems in the tropics. Despite of its importance, in atmosphere models, structure and dynamics of the vertical convection have not been expressed explicitly by grids but “parameterized” because the horizontal scale of convective clouds is too small to be expressed by grids of global models so far. By remarkable progress of computer power it is now possible to treat convective clouds explicitly equally as baroclinic eddies in middle-high latitudes. Nonhydrostatic ICosahedral Atmosphere Model (NICAM) developed at the Frontier Research Center for Global Change (FRCGC) is the first global atmosphere model to resolve convective systems in the tropics with a 3.5km mesh, at the highest resolution. The aqua-planet experiment by use of the model may be regarded as a tropical counterpart of Phillips' numerical experiment. Results of numerical experiments performed at FRCGC will be reported by focussing on various forms (or modes) of the occurence of convections and associated circulations in the tropics. On the basis of these experiments together with the observations the author will try to contrast phenomena and dynamics of the two worlds: The quasi-2-D vortex world in the middle-high latitudes and the convection-wave world in the tropics.