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EAMxx Technical Guide

The goal of this document is to describe the specific equations, parameterizations, and numerical methods used in the current version of EAMxx. Because our master-branch implementation changes every time we make a new commit, this documentation will also evolve continuously. As such, documentation for master should always be considered to be preliminary and under construction. If you want trustworthy documentation, pull it from an official model release.

Overview

Currently, EAMxx is only configured for km-scale convection-permitting runs. In order to provide scientifically-credible simulations at lower resolution, parameterizations for the following processes would be needed:

  1. deep convection
  2. gravity-wave drag
  3. energy fixer

The only configuration of EAMxx that is currently implemented is the convection-permitting version, commonly known as the Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM). Processes in EAMxx-SCREAM are:

  1. a non-hydrostatic version of the spectral-element dynamical core used by other E3SM Atmosphere Model versions1 with semi-Lagrangian tracer advection as described by Bradley et al. (2022)2
  2. turbulent mountain stress is crudely parameterized following Fiedler and Panofsky (1072)3 to reduce excessive winds around topography
  3. the Simple Higher-Order Closure (SHOC) parameterization from Bogenschutz and Krueger (2013)[@Bogenschutz_Krueger13], which handles turbulent diffusion, condensation/evaporation, and liquid cloud fraction
  4. an all-or-nothing ice cloud fraction parameterization that sets ice cloud fraction to 100% whenever cloud ice mass qi is less than a user-specified threshold set by default to 1e-5 kg/kg. This scheme also sets the total cloud fraction (used by microphysics) to the maximum of the liquid and ice cloud fraction.
  5. the effects of aerosol are prescribed via the Simple Prescribed Aerosol (SPA) scheme, which is very similar to MACv2-SP4
  6. the P3 microphysics scheme from Morrison and Milbrandt (2015)5 modified as described by Caldwell et al. (2021)6 to assume instantaneous liquid saturation adjustment for consistency with SHOC
  7. RTE/RRTMGP radiation from Pincus et al. (2019)7 rewritten in C++ for consistency and performance
  8. the CFMIP Observation Simulator Package (COSP) is also integrated into EAMxx, but currently only the ISCCP output is enabled

By default processes are called in this order, but which processes to include and in what order is modifiable at run time. After all atmospheric processes are called, output is written. Surface components are then called before the next atmosphere step starts. These processes are described in more detail in Caldwell et al. (2021)6. As in EAM, dynamics operates on a spectral element grid and all other processes use a finite-volume grid that divides each spectral element into 4 quadrilaterals. This physics grid is described in Hannah et al. (2021)8.

  1. Mark A. Taylor, Oksana Guba, Andrew Steyer, Paul A. Ullrich, David M. Hall, and Christopher Eldred. An energy consistent discretization of the nonhydrostatic equations in primitive variables. Journal of Advances in Modeling Earth Systems, 12(1):e2019MS001783, 2020. e2019MS001783 10.1029/2019MS001783. URL: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019MS001783, arXiv:https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019MS001783, doi:https://doi.org/10.1029/2019MS001783. ↩

  2. A. M. Bradley, P. A. Bosler, and O. Guba. Islet: interpolation semi-lagrangian element-based transport. Geoscientific Model Development, 15(16):6285–6310, 2022. URL: https://gmd.copernicus.org/articles/15/6285/2022/, doi:10.5194/gmd-15-6285-2022. ↩

  3. F. Fiedler and H. A. Panofsky. The geostrophic drag coefficient and the ‘effective’ roughness length. Quarterly Journal of the Royal Meteorological Society, 98(415):213–220, 1972. URL: https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.49709841519, arXiv:https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.49709841519, doi:https://doi.org/10.1002/qj.49709841519. ↩

  4. B. Stevens, S. Fiedler, S. Kinne, K. Peters, S. Rast, J. Müsse, S. J. Smith, and T. Mauritsen. Macv2-sp: a parameterization of anthropogenic aerosol optical properties and an associated twomey effect for use in cmip6. Geoscientific Model Development, 10(1):433–452, 2017. URL: https://gmd.copernicus.org/articles/10/433/2017/, doi:10.5194/gmd-10-433-2017. ↩

  5. Hugh Morrison and Jason A. Milbrandt. Parameterization of cloud microphysics based on the prediction of bulk ice particle properties. part i: scheme description and idealized tests. Journal of the Atmospheric Sciences, 72(1):287 – 311, 2015. URL: https://journals.ametsoc.org/view/journals/atsc/72/1/jas-d-14-0065.1.xml, doi:10.1175/JAS-D-14-0065.1. ↩

  6. P. M. Caldwell, C. R. Terai, B. Hillman, N. D. Keen, P. Bogenschutz, W. Lin, H. Beydoun, M. Taylor, L. Bertagna, A. M. Bradley, T. C. Clevenger, A. S. Donahue, C. Eldred, J. Foucar, J.-C. Golaz, O. Guba, R. Jacob, J. Johnson, J. Krishna, W. Liu, K. Pressel, A. G. Salinger, B. Singh, A. Steyer, P. Ullrich, D. Wu, X. Yuan, J. Shpund, H.-Y. Ma, and C. S. Zender. Convection-permitting simulations with the e3sm global atmosphere model. Journal of Advances in Modeling Earth Systems, 13(11):e2021MS002544, 2021. e2021MS002544 2021MS002544. URL: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021MS002544, arXiv:https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021MS002544, doi:https://doi.org/10.1029/2021MS002544. ↩↩

  7. Robert Pincus, Eli J. Mlawer, and Jennifer S. Delamere. Balancing accuracy, efficiency, and flexibility in radiation calculations for dynamical models. Journal of Advances in Modeling Earth Systems, 11(10):3074–3089, 2019. URL: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019MS001621, arXiv:https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019MS001621, doi:https://doi.org/10.1029/2019MS001621. ↩

  8. Walter M. Hannah, Andrew M. Bradley, Oksana Guba, Qi Tang, Jean-Christophe Golaz, and Jon Wolfe. Separating physics and dynamics grids for improved computational efficiency in spectral element earth system models. Journal of Advances in Modeling Earth Systems, 13(7):e2020MS002419, 2021. e2020MS002419 2020MS002419. URL: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020MS002419, arXiv:https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020MS002419, doi:https://doi.org/10.1029/2020MS002419. ↩