In general it is organised, as a huge tree, with the indentation below, showing different levels down that tree: 1) Deterministic data (stream oper): - origin and model
- type of data (analysis, forecast, etc)
- year
- month
- type of level (model level, pressure level, surface etc)
- dates, times, steps (for forecast type), levels (for non surface levels), parameters
2) Ensemble data (stream enda): - origin and model
- type of data (analysis, forecast, etc)year
- month
- type of level (model level, pressure level, surface etc)
- dates
- times, steps (for forecast type), levels (for non surface levels), parameters, members (for ensembles)
 The items on the lowest level in the trees below above are archived on the same tape. The tree structure can be easily understood by investigating the deepest UERRA Web MARS page (where one can select exactly which parameters are needed). All selectable items listed in the web listboxes on that page represent data occupying the same archiving tape.
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