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This page contains a few rules on the UERRA parameters. A complete list of all the parameters and GRIB2 encoding is given here.

UERRA parameters rules

Units

All fields shall use units as defined in GRIB Edition 2

Accumulations

All accumulations shall start from the beginning of the forecast
The initial state (forecast step zero) shall be a part of all forecasts, all members, etc.
The values of accumulated fields shall be set to zero for t=0

Instantaneous fields

Instantaneous fields shall be archived with a frequency defined here for each group of parameters and forecast type.

Parameters archived since previous post-processing

Some parameters (2m tmin/tmax, 10m wind gust) shall be archived with varying lenght of time range intervals (0-1/1-2/2-3/4-5/5-6/6-9/9-12/../27-30 as per here)

Fluxes

The flux sign convention will be positive downwards.

Missing values

Bitmaps shall be used to indicate missing values (i.e. Soil temperature (st) shall be coded using a bitmap, because there is no model output over the sea)

Grid and resolution

Each partner will provide their eps data on their native grid.
Grids are defined in GRIB2 using an accuracy of 1/1000000 (one millionth) of a degree.

Types of forecasts

The Control Forecast must be number 0,
The number of members is identical to the number of all EPS members plus the Control Forecast.

GRIB2 encoding

ECMWF encoding/decoding Software

ECMWF makes available a GRIB decoding library (GRIB-API) for the benefit of the WMO community. GRIB-API can be freely downloaded from here and the documentation can be found here. The GRIB-API provides a simplified access to GRIB2 headers through a set of virtual keys documented her

The version of GRIB-API which can recognise all UERRA parameters is currently under development and should be released to some extent by the 1st half of June. Until then please use the version 1.15.0 which can identify UERRA products as per below (paragraph 1).

GRIB2 encoding details

Section 1
Octets	Key name	Value	Description
6-7	centre	82	82 (Sweden)
10	tablesVersion	17	latest WMO table with some new definitions for UERRA
20	productionStatusOfProcessedData	8	operational UERRA products
		9	test UERRA products
21	typeOfProcessedData	0	Analysis products
		1	Forecast products

Deterministic system (both analysis and forecast products)

Section 4

Octets

Key name

Value

Description

8-9

productDefinitionTemplateNumber

0

Analysis and Forecast products (instantaneous)

(Analysis or forecast at a horizontal level or in a horizontal layer at a point in time (grib2/tables/17/4.0.table))

8

Analysis and Forecast products (statisticially processed = accumulated/min/max values)

(Average, accumulation, extreme values or other statistically processed values at a horizontal level or in a horizontal layer in a continuous or non-continuous time interval (grib2/tables/17/4.0.table))

Ensembe DA system (both analysis and forecast products)

Section 4
Octets	Key name	Value	Description
8-9	productDefinitionTemplateNumber	1	Analysis and Forecast products (instantaneous) (Individual ensemble forecast, control and perturbed, at a horizontal level or in a horizontal layer at a point in time (grib2/tables/17/4.0.table))
		11	Analysis and Forecast products (statisticially processed = accumulated/min/max values) (Individual ensemble forecast, control and perturbed, at a horizontal level or in a horizontal layer, in a continuous or non-continuous time interval (grib2/tables/17/4.0.table))
35	type of ensemble forecast	255	missing
36	perturbation number	2	Example for 2nd eps member of ensemble with 4 members (0/1/2/3)
37	number of forecasts in ensemble	4

Examples of GRIB2 files

	deterministic		ensemble DA
	AN	FC	AN	FC
Accumulations (evaporation)	N/A	grib dump	N/A	grib dump
Instantaneous
Maximum since previous post-processing
Minimum since previous post-processing
Parameter on soil level (soil temperature on soil level 1)	grib dump	grib dump