Equivalent finite volume and Eulerian spectral transform horizontal resolutions established from aqua-planet simulations

The equivalent resolutions for two different global dynamic cores are established when they are coupled to the sub-grid scale parametrization suite of the Community Atmosphere Model (CAM3). One core adopts the common Eulerian spectral transform formalism, the other adopts a finite volume approach. The equivalent resolutions are established over a range of resolutions employed today for climate models. The comparison is done in the context of the Aqua Planet Experiment (APE). Thus, it is based on the characteristics of free, unforced motions, due in large part to the dynamic component driven by the parametrized processes and explicit dissipation. The forced component arising from surface orography and land-ocean-sea-ice contrasts is not considered. The resolution equivalences are demonstrated for a number of model fields. These include selected time averaged, global and zonal averaged fields, the meridional structure of eddy kinetic energy and eddy temperature variance, the mean meridional eddy transports, the characteristics of tropical wave propagation and probability density functions of precipitation. These fields indicate that the 2 degrees finite volume model is equivalent to T42 spectral transform model, 1 degrees is equivalent to T85 and 0.5 degrees is equivalent to T170. This proportional relationship does not hold at lower resolutions.