E9.1 E3SM Assessment with CONUS RRM grid and the CAPT approach

Poster Title	A Study on the Summer Precipitation Bias in E3SM over the Central U.S. with the RRM Grid and the CAPT Approach
Authors	Xue Zheng, Chris Golaz, Shaocheng Xie, Wuyin Lin, Qi Tang
First Author	Xue Zheng
Session Type	E3SM/Integrated Session
Session ID	E9
Submission Type	Poster/Presentation
Group	Water Cycle
Experiment	Watercycle
Poster Link

Abstract

The summer precipitation bias over the central US is a persistent challenge for climate models and it is closely linked to surface temperature bias. The Energy Exascale Earth System Model (E3SM) v1 Atmosphere Model (EAM) has implemented many new features in the physical parameterizations and developed two different horizontal resolutions: 1^o (ne30) and 0.25^o(ne120). Each resolution has its own tuning parameter setting. It is important to assess the persistent precipitation bias over the central US in EAM v1 and exam how the bias respond to different model settings.

This study conducts EAM v1 5-year AMIP simulations and short-term hindcasts (i.e. CAPT simulations) for the summer of 2011 with the regular ne30 grid and the CONUS RRM grid (the resolution is 0.25^oover CONUS, and 1^o elsewhere) All simulations manifest a wet precipitation bias over the Rocky Mountains and a dry bias over the Great Plains. The relative differences in the biases among different settings are the same between AMIP and CAPT simulations. The results indicate that EAM v1 tends to generate too strong deep convection system slightly too west over the Rocky Mountains. The system is trapped in the west likely due to the unfavored environment east of it and the triggering mechanism of ZM scheme. EAM1 also tends to produce too weak northward moisture transport east of 100^oW, which has been found to be a key factor controlling the precipitation over the central US, especially during the nighttime. Increasing model resolution to 0.25^o can help reduce the portion of the ZM convective precipitation and generate stronger convection systems over the central US but it is still not good enough. The current tuning practice in EAM1 shows little impact on the diurnal cycle of precipitation, which is mainly controlled by the triggering mechanism of ZM scheme.

Acknowledgement: This work is supported by the CMDV-RRM Project for the Office of Science of the U.S. DOE. This work was performed under the auspices of the U.S. DOE by LLNL under contract DE-AC52-07NA27344. LLNL-ABS-758566