Introduction

This section shows how to configure and run OpenIFS and XIOS together.

First of all, it is necessary that OpenIFS is compiled with XIOS (see OpenIFS: Enable XIOS during compilation) and the XIOS executable is available in the experiment directory. OpenIFS should be run as usual (see 6.3 OpenIFS Running a Forecast), but adding the argument '--xios' to oifs_run. This will use by default 1 XIOS server, but in case of needing more servers, it can be done with '--xios --xios-nproc <arg>'.

It is also necessary to enable the 'LXIOS' switch in the 'NAMCT0' namelist (fort.4 file).

Output control: XML files

It is expected that users have knowledge on the use of XIOS which includes the creation of NetCDF files, computation of diagnostics, interpolations, data compression, interpretation of performance parameters, etc. Official documentation such as the user guide or tutorials is available on the webpage: https://forge.ipsl.jussieu.fr/ioserver. However, this section will explain XIOS aspects that are particular to OpenIFS.

OpenIFS and XIOS are controlled using different XML files:

• iodef.xml: it contains basic parameters to control the working mode of XIOS (attached or server mode, 1 or 2 levels of servers, etc), performance parameters, verbose level, etc.
• context_ifs.xml: it contains FullPos parameters to tune the vertical interpolations as well as two optimizations that might improve the execution time.
• axis_def_ifs.xml: it defines the different types of vertical levels available in OpenIFS: model levels, pressure levels, theta levels and PV levels.
• domain_def_ifs.xml: it defines the different domains (or types of grids) available in OpenIFS. By default, data can be output in the native grid (reduced Gaussian) or in a regular Gaussian grid with size 512x256.
• grid_def_ifs.xml: it defines the grids (XIOS terminology) available in OpenIFS used to map fields:
  • Grids for 2D fields are made of a single domain.
  • Grids for 3D fields are made of a domain and an axis.
• field_def_ifs.xml: it defines all the available fields to be output in OpenIFS:
  • Surface fields.
  • 3D fields in model levels.
  • 3D fields in pressure levels.
  • 3D fields in theta levels.
  • 3D fields in PV levels.
  • 3D PEXTRA fields in model levels.
• file_def_ifs.xml: it defines NetCDF files to be written. It allows you to configure many different parameters such as output frequency, compression, diagnostics, output mode (one file vs. multiple files), metadata, timeseries, etc.

Let’s see in more detail how to configure different features particular to OpenIFS-XIOS.

FullPos parameters

Optimizations for sending data from OpenIFS processes to XIOS servers

Define different vertical level values

Define different regular Gaussian domains

Define different grids from new axes and domains

Enable regular lat-lon grid output

Understanding output frequency, sampling frequency, NFRHIS and NFRPOS

Computational performance considerations