Improving Momentum Transport Processes in E3SM

We have modified the source spectrum parameterization of convectively generated gravity waves and have significantly improved the representation of the quasi-biennial oscillation (QBO) in the lower tropical stratosphere. 

Motivation: Transport of momentum throughout the atmosphere in large part controls the global circulation, and hence moisture and precipitation patterns. However, several momentum transport processes occur on scales much smaller than a global circulation model (GCM) grid box, and hence have to be parameterized. Improvements in the representation of subgrid momentum transport can lead to significant model improvements in the representation of wind stresses, moisture and precipitation patterns, and organized modes of variability. This project aims to improve the representation of subgrid momentum transport within convection and from orographic and convectively generated gravity waves, in order to improve existing biases in the representation of precipitation and surface stresses, as well as in the representation of the mean state and variability in the stratosphere in the Energy Exascale Earth System Model (E3SM).

Technical Approach: In this project we will (a) verify the parameterization of convective momentum transport (CMT) within the deep convection scheme, (b) implement a multiscale coherent structure parameterization (MCSP), (c) implement a new parameterization of orographic gravity waves, and (d) modify the source spectrum parameterization of convectively generated gravity waves (CGGWs). CMT parameterization and MCSP will be verified using the output from mesoscale simulations of convection, which will be performed using the Weather Research and Forecasting (WRF) model. Newly implemented orographic gravity wave parameterization and modifications to the parameterization of CGGWs will be evaluated using observations from super-pressure balloons. 

Anticipated Outcomes: We anticipate the above changes to E3SM will help to alleviate the following currently existing biases: double intertropical convergence zone, excessive wind stress over Southern Ocean, precipitation biases, including over tropical west Pacific, weak convectively-coupled waves (Kelvin and Madden-Julian Oscillation), too strong and too fast quasi-biennial oscillation in the lower stratosphere, too few sudden stratospheric warmings. The changes that will be implemented could also potentially improve the representation of El Nino Southern Oscillation.

Project Term: 
2018 to 2021
Project Type: 
Cooperative Agreement (CA)