Generate atm initial condition from analysis data
This is to document a new procedure for generating atm initial condition file from analysis data. The essence of the workflow is no different than the commonly used ones (e.g., CAM tool interpic) for generating initial condition for new grids from existing ones, namely, horizontal and vertical remapping from source data grid to target grid. The emphasis of this workflow is to make use of builtin functionalities of the powerful NCO. Necessary intermediate steps are introduced to facilitate the use of NCO utilities to generate dynamically reasonably balanced initial conditions that are most likely ready for model simulations without additional spinup to filter fast gravity waves. This is effectively realized by adjusting surface pressure field to account for the mismatch in topography between the source and destination grids. The workflow is first put together to generate input files for SCREAM project's initialized simulations using IFS analysis provided by the DYAMOND Initiative. It can be easily adapted to other analysis or model data, including remapping from initial conditions from other SE grids used by EAM.
The following illustration uses ne512 as target grid and IFS analysis as source data. The workflow will be streamlined to minimize user input and the intermediate codes (esp. IDL) will be hardened for portability.
Note that to generate the initial file for a specific grid (uniform resolution or RRM), the grid description file is required (a SCRIP or a .g file). For high-resolution grids, a .g grid file is preferred in order to use TempestRemap to generate high-order map file. See more in step 3.
NOTE: The procedure to generate new initial conditions has been built into into the HICCUP tool (see https://github.com/E3SM-Project/HICCUP), which is a set of flexible and robust python routines to automate and streamline the task of generating a new atmospheric initial condition for E3SM. It can use ERA5 reanlaysis data or regrid (either horizontal, vertical or both) an existing atmospheric initial condition file. HICCUP has its own surface adjustment routine that follows the original adjustment routine published by ECMWF, which was also reproduced in similar tools by Jerry Olson and Wuyin Lin. HICCUP was built with code readability and documentation as a top priority and includes some unit tests for adjustment routines. HICCUP has also successfully been used to generate initial conditions for ne1024 grids using large memory analysis nodes available at HPC centers. Development of HICCUP is ongoing and new features are planned, so any feedback or feature requests are welcome.