Two-dimensional Hadley circulation modeling as a test bed for high resolution climate simulation

A realistic two-dimensional Hadley circulation simulation has been developed under a SciDAC project to assess the performance of new physics schemes in a high-resolution climate model. The horizontal resolution of global climate simulations is increasing significantly, O (a few km), and schemes for model physics are being upgraded to achieve optimal performance. The Energy Exascale Earth System Model (E3SM) is a new generation global model developed by DOE, and a future version, also known as SCREAM, will use a 3 km horizontal mesh with cutting-edge schemes representing atmospheric turbulence and cloud microphysics. However, performance and lurking difficulties with these new physics schemes at such high-resolution global model are largely unknown. Ideally a series of global high-resolution simulations of sufficiently long duration are desired to assess performance. In practice current computing power is a limitation. We approach this problem by applying two-dimensional Hadley circulation modeling that simulates many types of clouds and scale interactions. These cannot be simulated by a single column model or a coarse-grid global model. The Hadley circulation is, to first order, representative of the general circulation and hence climate. It is a complicated phenomenon related to multiple interacting physical processes. Since two-dimensional simulation is simple and lightweight, we can save computation in the zonal direction and easily increase model resolution and the number of experimental cases. A test experiment has been completed using 2 km horizontal grid spacing. 50 days of time integration with 512 cores of CPU required only 4 days. The results show realistic features of the Hadley circulation and suggest the two-dimensional Hadley circulation modeling can serve as a testbed for assessing, inter alia, model parameterizations and their influence on the circulation. The model can also serve as a tool to study various aspects associated with the Hadley circulation.