## Overview.

The definitions described in this section are used at ECMWF for special purposes.

Element KSEC1(24) is set to 1 if an ECMWF local use definition is required or has been found in a GRIB message; element KSEC1(37) indicates which definition it is.

If KSEC1(24) is set to 0, no local use definition is present in the message.

Currently, the following definitions exist:

- Definition 1 - MARS labelling or ensemble forecast data
- Definition 2 - Cluster means and standard deviations
- Definition 3 - Satellite image data
- Definition 4 - Ocean model data
- Definition 5 - Forecast probability data
- Definition 6 - Surface temperature data
- Definition 7 - Sensitivity data
- Definition 8 - ECMWF re-analysis data
- Definition 9 - Singular vectors and ensemble perturbations
- Definition 10 - EPS tubes
- Definition 11 - Supplementary data used by the analysis
- Definition 13 - Wave 2D spectra direction and frequency
- Definition 14 - Brightness temperature
- Definition 15 - Seasonal forecast data
- Definition 16 - Seasonal forecast monthly mean data
- Definition 17 - Surface temperature or sea-ice data
- Definition 18 - Multi-analysis ensemble data
- Definition 19 - Extreme forecast index data
- Definition 20 - 4D variational increments
- Definition 21 - Sensitive area predictions
- Definition 22 - Coupled atmospheric, wave and ocean models (with hindcast support)
- Definition 23 - Coupled atmospheric, wave and ocean means (with hindcast support)
- Definition 24 - Satellite image simulation
- Definition 25 - 4DVar model errors
- Definition 26 - MARS labelling or ensemble forecast data (with hindcast support)
- Definition 27 - Forecasting Systems with Variable Resolution (Obsolete)
- Definition 30 - Forecasting Systems with Variable Resolution
- Definition 31 - EUROSIP products
- Definition 50 - Member State data
- Definition 190 -Multiple ECMWF local definitions
- Definition 191 - Free format data descriptor data
- Definition 192 - Multiple ECMWF local definitions

## Octets in section 1

The relation between the octets (bytes) in section 1 of a GRIB product and the elements in the array KSEC1 is illustrated below.

## Octets in section 1

Octet | KSEC1 element | Comments
--- | --- | ---
1-3 | - | Length of section 1
4 | 1 | Version number of code table 2
5 | 2 | Identification of centre (ECMWF = 98)
6 | 3 | Generating process identification number
7 | 4 | Grid definition
8 | 5 | Section 2/3 indication flag
9 | 6 | Parameter indicator
10 | 7 | Level indicator/satellite identifier
11 | 8 | Height/pressure of level
12 | 9 | Height/pressure of level
13 | 10 | Year
14 | 11 | Month
15 | 12 | Day
16 | 13 | Hour
17 | 14 | Minute
18 | 15 | Time unit indicator
19 | 16 | Time period
20 | 17 | Time period
21 | 18 | Time range indicator
22-23 | 19 | Number of products in an average
24 | 20 | Number of products missing from an average
25 | 21 | Century
26 | 22 | Sub-centre identifier
27-28 | 23 | Decimal scale factor
- | 24 | Flag to indicate local usage in section 1
29-40 | 25-36 | Zero
41 | 37 | ECMWF local GRIB usage definition identifier*
42 | 38 | Class
43 | 39 | Type
44-45 | 40 | Stream
46-49 | 41 | Version number or experiment identifier

* Local definition numbers 192 to 255 inclusive will never be used to define ECMWF local extensions to section 1, GRIB code. They are free to be defined and used by Member States.