12 November 2015

Dynamical Convergence on the Jet Stream in Aquaplanet AGCMs


Projecting the tropospheric shifts of the jet stream and the imbedded turbulent winds is a large challenge with important implications for predicting changes in regional precipitation patterns in the extratropics. To better understand uncertainty in the jet streams simulated in climate models, U.S. Department of Energy researchers at Pacific Northwest National Laboratory and collaborators at Cornell University investigated the possible convergence of jet position and intensity in global climate simulations. Analyzing a set of global atmospheric simulations in an aquaplanet at horizontal resolutions ranging from 30 km to 240 km, the team found a systematic poleward shift of the jet position with increasing model resolution. The poleward shift of the eddy-driven jet can be attributed to the smaller effective diffusivity of the model in the midlatitudes allowing more wave activity to survive the dissipation to reach the subtropical critical latitude for wave breaking. With increasing resolution, the eddy-driven westerlies show a consistent sign of convergence toward a more poleward position. In addition, the jet stream core intensity tends to decrease with resolution. Because of the prominent influence of the jet stream on midlatitude climate features such as storm tracks and blocking, these biases have undermined the effectiveness of climate models in not only simulating the present climate but also projecting future trends. These findings can serve as an important theoretical basis for the modeling centers across the world in their choice of the appropriate resolution of the atmospheric component for future generations of the Coupled Model Inter-Comparison project (CMIP6). 

L. Ruby Leung
Pacific Northwest National Laboratory (PNNL)
Lu, J, G Chen, LR Leung, DA Burrows, Q Yang, K Sakaguchi, and S Hagos.  2015.  "Towards the Dynamical Convergence on the Jet Stream in Aquaplanet AGCMs."  Journal of Climate 28(17): 6763–6782, doi:10.1175/JCLI-D-14-00761.1.

This manuscript benefited greatly from the very constructive comments of Edwin Gerber during the review process. This study is supported by the Office of Science of the U.S. Department of Energy as part of the Regional and Global Climate Modeling Program. PNNL is operated for DOE by Battelle Memorial Institute under Contract DE-AC05-76RL01830. GC and DAB are supported by NSF Grant ATM-1064079 and DOE Grant DE-FOA-0001036.