Changes to the Brewer-Dobson Circulation and cold point tropopause in perturbed-climate global storm-resolving model simulations

Global storm-resolving models (GSRMs), which have <5km grid horizontal grid spacing, have become increasingly common tools to study the atmosphere because of their ability to explicitly simulate deep convection that must be parameterized in traditional global climate models (GCMs). However, these models are computationally expensive to run for long periods of time. While GSRMs have shown promising results in simulating deep and overshooting convection, it is still uncertain whether these models can reproduce key climate processes occurring on longer time scales, like the Brewer-Dobson Circulation, with fidelity to the real world. Recently, the GFDL X-SHiELD global storm-resolving model was run freely at 3.25 km resolution for two years with a control simulation of the current climate as well as perturbed-climate simulations with uniform +4K SSTs and/or 4xCO2. We evaluate the simulated Brewer-Dobson Circulation in the X-SHiELD GSRM simulations by calculating the transformed Eulerian mean residual circulation and comparing it to ERA5 reanalysis. We find that the X-SHiELD control simulation reasonably reproduces the circulation observed in the ERA5 reanalysis. We then use the perturbed-climate simulations to investigate how the Brewer-Dobson Circulation may change in a warmer climate and compare the GSRM-simulated changes to those predicted from GCMs. We also examine trends in the tropical cold point tropopause, which regulates the amount of water vapor entering the lower stratosphere. Changes in the cold point height from the control to perturbed simulations far exceed changes in the cold point temperature, consistent with past GCM studies that have shown a rise in the tropopause in a warming climate. Overall, these results suggest that longer GSRM simulations may be useful tools to help understand changes in the cold point and stratospheric circulation due to climate change.