# [Greenline] IO Prototype

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- Shaped by:
- Appetite (FTEs, weeks):
- Developers: <!-- Filled in at the betting table unless someone is specifically required here -->

## Problem
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Finish and clean up left overs from last cycle. Requirements for IO POC are defined in this [document](#IO).

Functionality recap:

Design `IOMonitor`: that can be configured to write fields at configured time intervals to output files. The Monitor decides based on configuration what fields from the state it needs to pick.

- Output is NetCDF4. The monitor also re-writes the gridfile into a UGRID extended version. Datafiles are such that they can be loaded together with the UGRID-file

- Currently due to a lack of a complete *model state* (including all meta data) only prognostic fields are available.

Output fields are 3D with on model levels on the unstructured grid, no regridding.

## Appetite
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Several components of the task were explored in the last cycle an need to be combined and tested properly.

## Solution
<!-- The core elements we came up with, presented in a form that’s easy for people to immediately understand -->
Steps to be completed:
[#IO](https://hackmd.io/U202TVPoQveNej2xMbtUMw)

see below

## Rabbit holes
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## No-gos
<!-- Anything specifically excluded from the concept: functionality or use cases we intentionally aren’t covering to fit the ## appetite or make the problem tractable -->

## Progress
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- [x] Task 1 ([PR#451](https://github.com/C2SM/icon4py/pull/451)
- [x] contigurable field groups
- [x] write ugrid file
- [x] write data files
- [x] Netcdf (need netcdf4-python directly)
- [x] CF convention like
- [x] support for half level fields
- [ ] add physical height dimension (vct_a for now)?
- [x] allow for rolling files per group _1.nc,, _2.nc

- [ ] Documentation
- [ ] how to use?

- [x] Test
- [x] improve test coverage
- [x] integration test: check whether output is readable with uxarray