PNNL

The Science

To capture both large- and small-scale Earth system processes, global and regional models run in both fine and coarse modes, with grid spacing ranging from a few kilometers to hundreds of kilometers. Scientists remain unclear about how vertical motions in storm systems change transport of air masses and momentum across scales. Limited understanding of this process—referred to as convective momentum transport, or CMT—introduces large uncertainty into how these components are represented at different model resolutions.

A research team led by scientists at the U.S. Department of Energy's Pacific Northwest National Laboratory studied wind momentum transport by convection at different scales and used their new understanding to evaluate and improve a parameterization for large-scale models. Results showed for the first time a strong scale dependence of the time evolution and vertical structure of wind momentum transport in storms.

The Impact

CMT has a strong influence on global atmospheric circulations and Earth system processes, but model formulations often oversimplify its effects. This study provides a better understanding of CMT at different scales and new insights for improving simulations of circulations in global models.

Reference: Y.-C. Liu, J. Fan, K.-M. Xu, G.J. Zhang, "Analysis of Cloud-Resolving Model Simulations for Scale Dependence of Convective Momentum Transport." Journal of the Atmospheric Sciences 75(7), 2445-2472 (2018). [https://doi.org/10.1175/JAS-D-18-0019.1]