Performance of the HOMME dynamical core in the aqua-planet configuration of NCAR CAM4: equatorial waves

A new atmospheric dynamical core, named the High Order Method Modeling Environment (HOMME), has been recently included in the NCAR-Community Climate System Model version 4 (CCSM4). It is a petascale capa- ble high-order element-based conservative dynamical core developed on a cubed-sphere grid. We have examined the model simulations with HOMME using the aqua-planet mode of CAM4 (atmospheric component of CCSM4) and evaluated its performance in simulating the equatorial waves, considered a crucial element of climate variability. For this we compared the results with two other established models in CAM4 framework, which are the finite-volume (FV) and Eulerian spectral (EUL) dynamical cores. Although the gross features seem to be comparable, important differences have been found among the three dynamical cores. The phase speed of Kelvin waves in HOMME is faster and more satis- factory than those in FV and EUL. The higher phase speed is attributed to an increased large-scale precipitation in the up- per troposphere and a more top-heavy heating structure. The variance of the n= 1 equatorial Rossby waves is underesti- mated by all three of them, but comparatively HOMME sim- ulations are more reasonable. For the n= 0 eastward inertio- gravity waves, the variances are weak and phase speeds are too slow, scaled to shallow equivalent depths. However, the variance in HOMME is relatively more compared to the two other dynamical cores. The mixed Rossby-gravity waves are feeble in all the three cases. In summary, model simulations using HOMME are reasonably good, with some improve- ment relative to FV and EUL in capturing some of the im- portant characteristics associated with equatorial waves.