Understanding Changes in Cloud Simulations from E3SM Version 1 to Version 2
Scientists at Lawrence Livermore National Laboratory within the Atmospheric, Earth, and Energy Division, along with collaborators from scientists from Pacific Northwest National Laboratory and Brookhaven National Laboratory, examined the model behavior change in clouds from E3SMv1 to v2. The focus is to document clouds simulated by the E3SMv2 and understand what causes the model behavior change in clouds relative to E3SMv1 using the COSP satellite simulators.
The results from the sensitivity tests, through isolating the impact of changes in model parameters, provide more insights into future model development.
One robust improvement in E3SMv2 compared to its earlier version is the increase of stratocumulus clouds along the subtropical west coast of continents in both Hemispheres. But we also found E3SMv2 shows a slightly larger negative bias in total low clouds than E3SMv1 in other regions in tropical and subtropical oceans. From our sensitivity tests, we found these changes are mainly due to the re-tuning of CLUBB. The tuning made in MG2, ZM, and the use of the new trigger all help offset the reduction of clouds made by the CLUBB tuning over the tropical and midlatitude regions. But they play a bigger role in other types of clouds, such as the ZM tuning is mainly on optically intermediate and thick high clouds.