Preprints
https://doi.org/10.5194/gmd-2022-10
https://doi.org/10.5194/gmd-2022-10
Submitted as: development and technical paper
03 Feb 2022
Submitted as: development and technical paper | 03 Feb 2022
Status: this preprint is currently under review for the journal GMD.

Further improvement and evaluation of nudging in the E3SM Atmosphere Model version 1 (EAMv1)

Shixuan Zhang1, Kai Zhang1, Hui Wan1, and Jian Sun1,2 Shixuan Zhang et al.
  • 1Pacific Northwest National Laboratory, Richland, Washington, USA
  • 2National Center for Atmospheric Research, Boulder, CO, USA

Abstract. A previous study on the use of nudging in EAMv1 had an unresolved issue, namely a simulation nudged to EAMv1’s own meteorology showed non-negligible deviations from the free-running baseline simulation over some of the subtropical marine stratocumulus and trade cumulus regions. Here, we demonstrate the deviations can be substantially reduced by two changes in the nudging implementation: first, revising the sequence of calculations in a nudged EAM simulation to improve consistency with the free-running baseline; second, increasing the frequency of constraining data from 6-hourly to 3-hourly to better capture strong sub-diurnal variations.

The resulting improvements in climate representativeness motivate an investigation on the potential benefits of using newer reanalysis products with higher data frequency in nudged simulations that aim at capturing observed weather events. Simulations nudged towards 6-hourly ERA-Interim reanalysis or 6-hourly, 3-hourly, and hourly ERA5 reanalysis are evaluated against EAMv1’s own climatology, global-scale satellite retrievals of outgoing longwave radiation and precipitation, as well as in-situ measurements of air temperature, humidity, and winds from the Atmospheric Radiation Measurement (ARM) user facility. Our overall recommendation is to use the revised sequence of calculation and 3-hourly data from ERA5 for the nudged simulations.

The anthropogenic aerosol effects in various EAMv1 simulations are evaluated. For estimating the global mean effect, the source of constraining data has a relatively small impact. Consistent with conclusions from previous studies, in order to obtain  estimates of global mean aerosol effects that are consistent with results from the free-running baseline, nudging the horizontal winds but not air temperature is recommended.

Shixuan Zhang et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2022-10', Anonymous Referee #1, 20 Mar 2022
    • AC1: 'Reply on RC1', Shixuan Zhang, 30 Apr 2022
  • RC2: 'Comment on gmd-2022-10', William Collins, 21 Mar 2022
    • AC2: 'Reply on RC2', Shixuan Zhang, 30 Apr 2022

Shixuan Zhang et al.

Data sets

Data and figures for the analysis Shixuan Zhang, and Kai Zhang https://zenodo.org/record/5839008#.YeHqmRPMJTY

Model code and software

EAM source codes and scripts for nudging experiments E3SM developers, Shixuan Zhang, Kai Zhang, and Jian Sun https://zenodo.org/record/5532606#.YeHp3RPMJTY

Shixuan Zhang et al.

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Short summary
In this study, we demonstrate that (1) revising the sequence of calculations and using higher frequency constraining data can substantially improve the climate representativeness of a nudged simulation; (2) using the newer ERA5 reanalysis product with higher data frequency is beneficial to improve the agreement between nudged simulations and observations; and (3) nudging the horizontal winds but not air temperature is recommended for the estimates of global mean aerosol effects in EAMv1.