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Title: Impact of numerical choices on water conservation in the E3SM Atmosphere Model version 1 (EAMv1)

The conservation of total water is an important numerical feature for global Earth system models. Even small conservation problems in the water budget can lead to systematic errors in century-long simulations. This study quantifies and reduces various sources of water conservation error in the atmosphere component of the Energy Exascale Earth System Model. Several sources of water conservation error have been identified during the development of the version 1 (V1) model. The largest errors result from the numerical coupling between the resolved dynamics and the parameterized sub-grid physics. A hybrid coupling using different methods for fluid dynamics and tracer transport provides a reduction of water conservation error by a factor of 50 at 1° horizontal resolution as well as consistent improvements at other resolutions. The second largest error source is the use of an overly simplified relationship between the surface moisture flux and latent heat flux at the interface between the host model and the turbulence parameterization. This error can be prevented by applying the same (correct) relationship throughout the entire model. Two additional types of conservation error that result from correcting the surface moisture flux and clipping negative water concentrations can be avoided by using mass-conserving fixers. With allmore » four error sources addressed, the water conservation error in the V1 model becomes negligible and insensitive to the horizontal resolution. The associated changes in the long-term statistics of the main atmospheric features are small. A sensitivity analysis is carried out to show that the magnitudes of the conservation errors in early V1 versions decrease strongly with temporal resolution but increase with horizontal resolution. The increased vertical resolution in V1 results in a very thin model layer at the Earth's surface, which amplifies the conservation error associated with the surface moisture flux correction. We note that for some of the identified error sources, the proposed fixers are remedies rather than solutions to the problems at their roots. Future improvements in time integration would be beneficial for V1.« less
Authors:
 [1] ;  [1] ; ORCiD logo [2] ;  [1] ;  [1] ;  [1] ; ORCiD logo [3] ;  [4] ;  [5] ;  [1] ; ORCiD logo [1] ; ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [3] ;  [3] ;  [3]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  5. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Report Number(s):
PNNL-SA-129738; LLNL-JRNL-741223; BNL-207903-2018-JAAM
Journal ID: ISSN 1991-9603
Grant/Contract Number:
AC06-76RL01830; AC52-07NA27344; AC05-00OR22725; AC02-05CH11231; SC0012704
Type:
Accepted Manuscript
Journal Name:
Geoscientific Model Development (Online)
Additional Journal Information:
Journal Name: Geoscientific Model Development (Online); Journal Volume: 11; Journal Issue: 5; Journal ID: ISSN 1991-9603
Publisher:
European Geosciences Union
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Environmental sciences; 54 ENVIRONMENTAL SCIENCES
OSTI Identifier:
1457765
Alternate Identifier(s):
OSTI ID: 1458643; OSTI ID: 1462399