Title: Short‐term time step convergence in a climate model

Abstract

Abstract This paper evaluates the numerical convergence of very short (1 h) simulations carried out with a spectral‐element (SE) configuration of the Community Atmosphere Model version 5 (CAM5). While the horizontal grid spacing is fixed at approximately 110 km, the process‐coupling time step is varied between 1800 and 1 s to reveal the convergence rate with respect to the temporal resolution. Special attention is paid to the behavior of the parameterized subgrid‐scale physics. First, a dynamical core test with reduced dynamics time steps is presented. The results demonstrate that the experimental setup is able to correctly assess the convergence rate of the discrete solutions to the adiabatic equations of atmospheric motion. Second, results from full‐physics CAM5 simulations with reduced physics and dynamics time steps are discussed. It is shown that the convergence rate is 0.4—considerably slower than the expected rate of 1.0. Sensitivity experiments indicate that, among the various subgrid‐scale physical parameterizations, the stratiform cloud schemes are associated with the largest time‐stepping errors, and are the primary cause of slow time step convergence. While the details of our findings are model specific, the general test procedure is applicable to any atmospheric general circulation model. The need for more accurate numericalmore » treatments of physical parameterizations, especially the representation of stratiform clouds, is likely common in many models. The suggested test technique can help quantify the time‐stepping errors and identify the related model sensitivities.« less

Authors:

Wan, Hui ^[1]; Rasch, Philip J. ^[1]; Taylor, Mark A. ^[2]; Jablonowski, Christiane ^[3]

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+ Show Author Affiliations

1. Pacific Northwest National Laboratory Richland Washington USA
2. Sandia National Laboratories Albuquerque New Mexico USA
3. Department of Atmospheric, Oceanic and Space Sciences University of Michigan Ann Arbor Michigan USA

Publication Date:

Wed Feb 11 00:00:00 EST 2015

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Oak Ridge Leadership Computing Facility (OLCF); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1240461

Alternate Identifier(s):

OSTI ID: 1208770; OSTI ID: 1214706; OSTI ID: 1240463

Report Number(s):

PNNL-SA-103971
Journal ID: ISSN 1942-2466

Grant/Contract Number:  

DE‐AC05‐76RL01830; AC05-76RL01830; AC04-94AL85000

Resource Type:

Published Article

Journal Name:

Journal of Advances in Modeling Earth Systems

Additional Journal Information:

Journal Name: Journal of Advances in Modeling Earth Systems Journal Volume: 7 Journal Issue: 1; Journal ID: ISSN 1942-2466

Publisher:

American Geophysical Union (AGU)

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; convergence; climate model; short-term; time step size