Inventory Conventions#

Every emission miem::Source names an inventory convention (its convention_ field) that tells MIEM how the source’s NetCDF files are laid out on disk. The convention is a contract about variable names, dimensions, and units – not about the science of the inventory itself. In v1 MIEM supports a single convention, "eccad"; any other value is rejected as UnknownConvention when the emissions builder builds the runtime.

Why ECCAD#

MIEM’s reference emission inventories are distributed through ECCAD [AERISSEDOO26] (Emissions of atmospheric Compounds and Compilation of Ancillary Data, https://eccad.aeris-data.fr/), the atmospheric-emissions data repository hosted by AERIS. Datasets such as CAMS-GLOB-ANT (anthropogenic) and GFAS (biomass burning) are published there in a consistent NetCDF layout, and that layout is what MIEM’s "eccad" convention encodes. Standardizing on the ECCAD layout means a host model can point MIEM at a freshly downloaded inventory without writing a bespoke reader for each product.

This is a file-format dependency, not a network or runtime dependency: MIEM never contacts ECCAD. A user (or musica’s translator) downloads the files ahead of time and hands MIEM a concrete, already-resolved path through Source::file_pattern_.

What the convention assumes#

The "eccad" convention expects each file to provide, per emitted species:

  • a flux variable keyed by the inventory’s species name,

  • a mass-flux unit of kg m-2 s-1 (the canonical ECCAD emission unit),

  • a time dimension MIEM interpolates across successive slices, and

  • a horizontal cell dimension already on the target grid (v1 does no regridding).

The inventory’s species names rarely match the chemical mechanism’s names. That gap is closed after the file is read, by the source’s SpeciesMap, which rewrites inventory-named emission flux onto the mechanism species MICM solves for.

Non-conforming files#

Inventories that do not follow the ECCAD layout (legacy CEDS files, custom research products) are not read with a second hard-coded convention. Instead, upstream tooling attaches a dataset descriptor that names the variable prefix, units, and dimension names so the file can be adapted to the canonical layout. The descriptor mechanism is defined in the configuration schema and resolved by musica before MIEM runs; the load-time versus runtime split is described in the configuration architecture note (docs/config-architecture.md in the repository). For v1, only "eccad" is accepted directly.