Introduction

During these first stages of the proof-of-concept phase of C3S seasonal forecast activity, we have been working in standardise to define a standard for the data provision in netCDF. This standard is described below.

The proposal is constrained by the CF convention, and we have also tried not to diverge from specifications coming from other well established communities: SPECS and CMIP5/6

Additionally ACDD has been also taken into account when defining the data discovery related metadata.

In that senseHence, the following links are valuable sources of information that have informed the definition of this proposal:

...

SPECS file content and format, data structure and metadata

CMIP5 list of variables

CMIP6 Data Request: MIP variables search

ACDD convention

Examples

Some example files have been created following the guidelines contained in this document.

View file

name	ncfiles.tgz
height	150

Encoding Guide for netCDF files conforming to C3S-0.1

Global attributes

The following properties are intended to provide information about where the data came from and what has been done to it. This information is mainly for the benefit of human readers and data discovery mechanisms. The attribute values are all character strings. When an attribute appears both globally and as a variable attribute, it is the variable’s version which has precedence.

To identify the type of data

A way of labelling hindcasts and forecasts to match them needs to be devised and could be included in the future in this attribute or will need a different attribute

Attribute Name	Value	Examples	Comment
Conventions	CF_convention_string C3S-0.1 [Other convention] :...	"CF-1.6 C3S-0.1"	Multiple conventions may be included (separated by blank spaces)
title	A controlled vocabulary will be provided"<short institution name> seasonal forecast model output prepared for C3S" CF: Free text ACDD (highly recommended)	"IPSL-CM5A-LR ECMWF seasonal forecast model output prepared for CMIP5 RCP4.5C3S"	A short phrase or sentence describing the dataset. In many discovery systems, the title will be displayed in the results list from a search, and therefore should be human readable and reasonable to display in a list of such names <short institution name> is the first element of the comma-separated list of values of the corresponding "institution" attribute
references	URIs (such as a URL or DOI) for papers or other references. A valid doi is recommended CF: Free text	"doi:10.5194/gmd-8-1509-2015"	Published or web-based references that describe the data or methods used to produce it.
source	A methodology to build this attribute will be provided	"world model v.0.1" "model-generated, GloSea5-GC2" "IPSL-CM5A-LR (2010) : atmos : LMDZ4 (LMDZ4_v5, 96x95x39); ocean : ORCA2 (NEMOV2_3, 2x2L31); seaIce : LIM2 (NEMOV2_3); ocnBgchem : PISCES (NEMOV2_3); land : ORCHIDEE (orchidee_1_9_4_AR5)"	The method of production of the original data. If it was model-generated, source should name the model and its version, as specifically as it could be useful
institution	A controlled vocabulary will be provided CF: Free text	"Met Office"	Specifies where the original data was produced. The name of the institution principally responsible for originating this data.
contact	Copernicus User Support URI should be used http://copernicus-support.ecmwf.int CF: Free text	"http://copernicus-support.ecmwf.int"
project	"C3S Seasonal Forecast" should be used CF: Free text	"C3S Seasonal Forecast"
creation_date	SPECS: YYYY-MM-DDThh:mm:ss<zone> ISO 8601:2004 extended format	"2011-06-24T02:53:46Z"	The date on which this version of the data was created. Modification of values implies a new version, hence this would be assigned the date of the most recent values modification. Metadata changes are not considered when assigning the creation_date NOTE: The ACDD 1.3 names this attribute as date_create SPECS conventions will be followed
comment	Free text	"Produced by University of Hamburg for DWD at ECMWF HPC facilities" "Run by CMCC at CINECA"	Miscellaneous information about the data, not captured elsewhere.
forecast_type	"forecast" or "hindcast"	"forecast"
history	Each line should begin with a timestamp indicating the date and time of day when the program was executed CF: Free Text	"Produced using CDS Toolbox on 1/6/2016" "Model raw output postprocessing with modelling environment (IMDI) at DKRZ: URL: http://svn-mad.zmaw.de/svn/mad/Model/IMDI/trunk, REV: 3436 2011-07-17T15:14:45Z CMOR rewrote data to comply with CF standards and CMIP5 requirements."	To record relevant information, such as the command history which led to this file being produced. Provides an audit trail for modifications to the original data. Well-behaved generic netCDF filters will automatically append their name and the parameters with which they were invoked to the global history attribute of an input netCDF file
commit, iso_lineage or lineage	Free text (ISO Lineage model 19115-2)	"Produced using CDS Toolbox v1.0"	Trace of the tools/scripts used. Either this attribute or the "history" attribute needs to include information about the versioning of the software used to create the data. This is related with some of the EQC activities (WP4 of QA4SEAS). ISO 19115-2 defines a linage model where this is been considered.
summary	The content will be provided ACDD (highly recommended): Text, defined phrase		A short paragraph describing the dataset
keywords	The content will be provided ACDD (highly recommended) : text, controlled vocabulary		A comma separated list of key words and phrases.
forecast_reference_time	SPECS: YYYY-MM-DDThh:mm:ssZ NOTE: This is ISO 8601:2004 extended format, but time zone is required to be UTC	"2011-06-01T00:00:00Z"	time of the analysis from which the forecast was made Introduced as global attribute to keep compatibility with SPECS NOTE: This works fine for SPECS data structure, i.e. one variable per start time per file

Spatial Coordinates

...

Values (1x1deg grid) prescribed:
dimension lat=181

[-90. , -89. , ..., 0., ... 90.]

...

[0. , 1. , ..., 358., 359.]

...

Pa

...

This is also referred to as isobaric level by some tools
Values prescribed:
dimension plev=11

[925., 850., 700., 500., 400., 300., 200., 100., 50., 30., 10.]
(NOTE: values here written in hPa, they should be Pa)

...

m

...

CMIP5:

2mtemp: 1.
10mu/v: 1.

...

CMIP5:

2mtemp: 10.
10mu/v: 30.

...

Used for single level fields (height, soil,SST)

e.g. 2 m (for Temperature)

...

C3S: string

...

C3S: realization_dim

CF: a different name is needed for dim/variable
(see comment)

...

Time Coordinates

...

SPECS: days
C3S: requested units can be relaxed to equivalent time units

...

The interval of time between the forecast reference time and the valid time

Boundaries not needed when this time coordinate is used for instantaneous values (note that "time:point" is used as cell_method in those cases)

...

time

...

SPECS: "days since 1850-01-01"

C3S: requested units can be relaxed to equivalent time units

...

Time for which the forecast is valid

Boundaries not needed when this time coordinate is used for instantaneous values (note that "time:point" is used as cell_method in those cases)

NOTE: Definitions for "leadtime" and "time" have been taken from SPECS. The introduction of "reftime" as a variable has been adapted from SPECS global attribute description for the forecast reference time.

NOTE: Even though there are different requested time steps among the variables (6h, 12h, 24h), just one set of time axes has been defined, as that would be enough when applying the requirement of "one variable per file"

Cell boundaries

As described in section 7.1 Cell Boundaries of CF convention.

Info

To represent cells we add the attribute bounds to the appropriate coordinate variable(s). The value of bounds is the name of the variable that contains the vertices of the cell boundaries. We refer to this type of variable as a "boundary variable." A boundary variable will have one more dimension than its associated coordinate or auxiliary coordinate variable. The additional dimension should be the most rapidly varying one, and its size is the maximum number of cell vertices. Since a boundary variable is considered to be part of a coordinate variable’s metadata, it is not necessary to provide it with attributes such as long_name and units

...

where to put the time coordinate (beginning, middle, end of the bounds) ?

e.g.
time=20160922 06
timebounds = [20160922 00, 20160922 06]

for 24h time steps:

[0,24] is that convention always valid?

...

Values (1x1deg grid) prescribed:

[0., 1.], [1., 2.], ... [359., 360.]

...

The following template should be followed in constructing this string: '<model_id> : atmosphere: <model_name> (<technical_name>, <resolution_and_levels>); ocean: <model_name> (<technical_name>, <resolution_and_levels>); sea ice: <model_name> (<technical_name>); land: <model_name> (<technical_name>)'' Additional explanatory information may follow the required information. NOTE that for some models, it may not make much sense to include all these components. The first portion of the string, “model_id”, should be built using the following template: "model_name-vYYYYMMDD" where YYYYMMDD is the release date of that version of the model (the date when it was first used)	"System4-v20111101: atmos: IFS (CY36R4, TL255L91); ocean: NEMOv3.0 (ORCA1_z42, 1x1L42); Local modifications in NEMOv3.0 (dynamic memory, flexible output, surface flux forcing, closure of frewsh water budget). FLAKE lake model "	The method of production of the original data. If it was model-generated, source should name the model and its version, as specifically as it could be useful. It is a character string fully identifying the model and version used to generate the output. It should include information concerning the component models. Note that information about changes in the individual components respect to the "official" releases should be included (e.g. a different bathymetry) The "source" attribute should include as much information as possible to not just identify the model but to brief the user about it
institute_id	Controlled Vocabulary: "ecmf" for ECMWF "egrr" for Met Office "lfpw" for Météo-France "edzw" for DWD "cmcc" for CMCC	"edzw"	Standardized 4 characters identifier of the institution that produced the data; NOTE all the values come from abbreviations of WMO/GRIB "originating centre" table, except CMCC (not available there)
institution	Controlled Vocabulary: "ECMWF, European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom" "Met Office, Exeter, United Kingdom" "Météo-France, Toulouse, France" "DWD, Deutscher Wetterdienst, Offenbach, Germany" "CMCC, Centro Euro-Mediterraneo sui Cambiamenti Climatici, Bologna, Italy" CF: Free text	"Météo-France, Toulouse, France"	Specifies where the original data was produced. The name of the institution principally responsible for originating this data. NOTE: The first element of the comma-separated list of values will be used as a shortened version of this attribute in some of the other global attributes ('summary', 'title')
contact	Copernicus User Support URI should be used http://copernicus-support.ecmwf.int CF: Free text	"http://copernicus-support.ecmwf.int"
project	"C3S Seasonal Forecast" should be used CF: Free text	"C3S Seasonal Forecast"
creation_date	SPECS: YYYY-MM-DDThh:mm:ss<zone> ISO 8601:2004 extended format	"2011-06-24T02:53:46Z"	The date on which this version of the data was created. Modification of values implies a new version, hence this would be assigned the date of the most recent values modification. Metadata changes are not considered when assigning the creation_date NOTE: The ACDD 1.3 names this attribute as "date_create". The name "creation_date" has been used following SPECS convention.
comment	Free text	"Produced by University of Hamburg for DWD at ECMWF HPC facilities" "Run by CMCC at CINECA"	Miscellaneous information about the data, not captured elsewhere.
forecast_type	Controlled Vocabulary "forecast" or "hindcast"	"forecast"	To identify the type of data
modeling_realm	Controlled Vocabullary "atmos", "ocean", "land", "landIce", "seaIce", "aerosol", "atmosChem", "ocnBgchem"	"seaIce"	A string that indicates the high-level modelling component that is particularly relevant to the variable encoded Controlled vocabulary taken from SPECS Value depends on the variable (see "global attributes" column in variables tables)
frequency	Controlled Vocabulary "mon", "day", "12hr", "6hr", "fix"	"day"	A string indicating the interval between individual time-samples. Controlled vocabulary taken from SPECS (extended to include "12hr" data) Value depends on the variable (see "global attributes" column in variables tables)
level_type	Controlled Vocabulary "surface", "pressure", "soil"	"pressure"	A string indicating the type of the level where the variable comes from Value depends on the variable (see "global attributes" column in variables tables)
history	Empty string	""	To avoid this attribute being polluted by usual netCDF tools, it must be enforced to an empty string.
commit	timestamp + URL of a commit in a CVS repository	"2017-04-01T13:48:25Z https://software.ecmwf.int/stash/projects/C3SS/repos/ecmf/System4_v20111101"	This attribute intends to keep trace of the tools/scripts used to post-process the data output from the model. Ideally it should contain the link to a repository containing the specific set of tools and scripts needed to reproduce the same data from the model output. It is highly desirable to have that traceability information. As a surrogate when the previous is not feasible it should include the timestamp followed by an URL pointing to the C3S documentation repository of the correspondent model version (properly labelled with the <model_id> introduced in 'source" attribute)
summary	Controlled Vocabulary: "Seasonal Forecast data produced by <short institution name> as its contribution to the seasonal forecast activity of the Copernicus Climate Change Service (C3S). The data has global coverage with a 1-degree horizontal resolution and spans for around 6 months since the start date" ACDD (highly recommended)	"Seasonal Forecast data produced by DWD as its contribution to the seasonal forecast activity of the Copernicus Climate Change Service (C3S). The data has global coverage with a 1-degree horizontal resolution and spans for around 6 months since the start date"	A short paragraph describing the dataset <short institution name> is the first element of the comma-separated list of values of the corresponding "institution" attribute
keywords	Fixed string "Seasonal Forecasts, C3S, ECMWF, Copernicus, Climate Change, Climate Services, Earth Science Services, Environmental Advisories, Climate Advisories" ACDD (highly recommended)		A comma separated list of key words and phrases. NOTE: This attribute is likely to be modified in the future, once the contents of the Thesaurus for CDS faceting will be defined
forecast_reference_time	SPECS: YYYY-MM-DDThh:mm:ssZ NOTE: This is ISO 8601:2004 extended format, but time zone is required to be UTC	"2011-06-01T00:00:00Z"	time of the analysis from which the forecast was made Introduced as global attribute to keep compatibility with SPECS (note that works fine for SPECS data structure, i.e. one variable per start time per file)

Spatial Coordinates

Type (CMIP5)	Coordinate Name (CMIP5)	Dimension Names (CMIP5)	Axis	standard_name	long_name (CMIP5)	units (CF canonical units)	positive	valid_min (CMIP5)	valid_max (CMIP5)	bounds	Notes
double	lat	lat	Y	latitude	latitude	degrees_north	N/A	-90.	90.	lat_bnds	Values (1x1deg grid) prescribed: center of 1-degree cells dimension lat=180 [-89.5, -88.5 , ..., -0.5, 0.5 ... 89.5]
double	lon	lon	X	longitude	longitude	degrees_east	N/A	0.	360.	lon_bnds	Values (1x1deg grid) prescribed: center of 1-degree cells dimension lon=360 [0.5 , 1.5 , ..., 358.5, 359.5]
double	plev	plev	Z	air_pressure	pressure	Pa	down	N/A	N/A		This is also referred to as isobaric level by some tools Values prescribed: dimension plev=11 [925., 850., 700., 500., 400., 300., 200., 100., 50., 30., 10.] (NOTE: values here written in hPa, they should be Pa)
double	plev	plev	Z	air_pressure	pressure	Pa	down	N/A	N/A
double	depth	depth	Z	depth	depth	m	down	N/A	N/A	depth_bnds	Only used for soil model levels NOTE: Number and depth of levels is not prescribed by C3S
double	height	(scalar auxiliary coordinate)	Z	height	height	m	up or down	CMIP5: 2mtemp: 1. 10mu/v: 1.	CMIP5: 2mtemp: 10. 10mu/v: 30.		Used for single level fields (height, soil,SST) e.g. 2 m (for Temperature)
C3S: string	realization	str31=31	E	realization	realization	1	N/A	N/A	N/A		members are not a physical quantity. Realization is a discrete coordinate and the members its categorical values (ordered or non-ordered ones) SPECS approach: rXXiYYpZZ

NOTE about the horizontal coordinates: The regridding procedure to provide the data in the 1-degree grid must take into account that the full definition of the gird cells is given by the cell boundaries (lat_bnds, lon_bnds)

Time Coordinates

Type

Coordinate Name

Dimension Names

Axis

standard_name

long_name

calendar

units

bounds

Notes

double

reftime

N/A

forecast_reference_time

"Start date of the forecast"

gregorian

UDUNITS time units
e.g.
"hours since YYYY-MM-DD hh:mm:ss TZhh:TZmm"

N/A

In SPECS it is only given as a "global_attribute"
It has been additionally introduced here as a coordinate variable to ease future netCDF management (e.g. file merging)

double

leadtime

N/A

forecast_period

"Time elapsed since the start of the forecast"

N/A

SPECS: days
C3S: requested units can be relaxed to equivalent time units

leadtime_bnds

The interval of time between the forecast reference time and the valid time

Boundaries not needed when this time coordinate is used for instantaneous values (note that "time:point" is used as cell_method in those cases)

When boundaries are required, the value of the coordinate must be in the centre of the correspondent time cell boundaries

double

time

leadtime

N/A

time

"Verification time of the forecast"

gregorian

SPECS: "days since 1850-01-01"

C3S: requested units can be relaxed to equivalent time units

time_bnds

Time for which the forecast is valid

Boundaries not needed when this time coordinate is used for instantaneous values (note that "time:point" is used as cell_method in those cases)

When boundaries are required, the value of the coordinate must be in the centre of the correspondent time cell boundaries

NOTE: Definitions for "leadtime" and "time" have been taken from SPECS. The introduction of "reftime" as a variable has been adapted from SPECS global attribute description for the forecast reference time.

NOTE: Even though there are different requested time steps among the variables (6h, 12h, 24h), just one set of time axes has been defined, as that would be enough when applying the requirement of "one variable per file"

Warning

"leadtime" has been selected as dimension (instead of "time") for both time and leadtime. That means "leadtime" is the coordinate and "time" is an auxiliary coordinate

This diverges from SPECS (where "time" was the name of the dimension and the coordinate, and "leadtime" was an auxiliary coordinate)
Here it has been done like that because
1. both reftime and leadtime are the relevant (let's say "orthogonal") coordinates coming from the relationship time = reftime + leadtime
2. doing like that has some advantages when merging netCDF files ("leadtime" can be easily shared by different variables in a merged file, while "time" cannot)

Cell boundaries

As described in section 7.1 Cell Boundaries of CF convention.

Info

To represent cells we add the attribute bounds to the appropriate coordinate variable(s). The value of bounds is the name of the variable that contains the vertices of the cell boundaries. We refer to this type of variable as a "boundary variable." A boundary variable will have one more dimension than its associated coordinate or auxiliary coordinate variable. The additional dimension should be the most rapidly varying one, and its size is the maximum number of cell vertices. Since a boundary variable is considered to be part of a coordinate variable’s metadata, it is not necessary to provide it with attributes such as long_name and units

Bounds Name	Dimensions	Comments
time_bnds	leadtime, bnds
leadtime_bnds	leadtime, bnds
lat_bnds	lat, bnds	Values (1x1deg grid) prescribed: [-90., -89.], [-89., -88.], ... [89., 90.]
lon_bnds	lon, bnds	Values (1x1deg grid) prescribed: [0., 1.], [1., 2.], ... [359., 360.]
depth_bnds	depth, bnds	Should define the full vertical extent of the soil model layers

Grid mapping

Info

As described in section 5.6 Grid Mappings and Projections of CF convention. (see quote below)

When the coordinate variables for a horizontal grid are longitude and latitude, a grid mapping variable with "grid_mapping_name" of "latitude_longitude" may be used to specify the ellipsoid and prime meridian.

Following that, it has been decided to include, as mandatory, in this C3S netcdf encoding guide the following variable

Code Block
char hcrs ; hcrs:grid_mapping_name = "latitude_longitude" ;

Variables

Common attributes

The following attributes must be included in all the variables:

attribute name	value	comment
grid_mapping	hcrs

Conditional attributes

The following attributes may be included in the attribute list for a given variable if the conditions specified are fulfilled:

attribute name	value	comment
_FillValue	Set by netCDF library	Those attributes must be included ONLY when the variable has missing values. If they are NOT present in the actual data field values, they should NOT be included as variable attributes.
missing_value	Set by netCDF library

Candidate attributes

The following attributes may be included in the attribute list for a given variable at a later date as this standard evolves:

attribute name	value	comment
valid_max	TBD	see below
valid_min	TBD	see below

Info

title	valid range attributes

Both "valid_min" and "valid_max" attributes should be included as variable attributes, but a set of sensible values for each and every variable needs to be provided.

In the meantime, it is proposed not to include them and just bear in mind that they will be required to be introduced at some point in the future.

Static Fields

Grid mapping

As described in section 5.6 Grid Mappings and Projections of CF convention.

Info
When the coordinate variables for a horizontal grid are longitude and latitude, a grid mapping variable with `grid_mapping_name` of `latitude_longitude` may be used to specify the ellipsoid and prime meridian.

Code Block
char latitude_longitude ; latitude_longitude:grid_mapping_name = "latitude_longitude" ;

NOTE: Wouldn't a different name be more appropriate? (e.g. CRS as in CF examples)

Variables

NOTE: coordinates should list first of all the auxiliary coordinate(s) and then all the other coordinates.... SHOULD reftime, leadtime and realization be included as well????

NOTE: type double/real????

Static Fields

attributes

name (CMIP5)	dimensions	standard_name	long_name (CMIP5)	units	coordinates

grid_mappingNOTES

valid_min	valid_max	global attributes
sftlf	lat,lon	land_area_fraction	"Land Area Fraction"	1	"lat lon"

latitude_longitude

0

1

"frequency":"fix"
"level_type": "surface"
"modeling_realm":"atmos"

orog

lat,lon

surface_altitude

"Surface Altitude"

m

"lat lon"

"frequency":"fix"
"level_type": "surface"
"modeling_realm":"atmos"

"lat lon"latitude_longitude

Surface Fields (defined at a given height level)

...

attributes

name
(CMIP5/6&C3S) dimensions standard_name long_name
(CMIP5/6&C3S) units coordinates cell_methods valid_min
grid_mapping
valid_max global attributes NOTES
tas
time
leadtime,lat,lon air_temperature "Near-Surface Air Temperature" K
"reftime realization time leadtime height
time
lat lon"

"leadtime: point"

C3S: required
CF: recommended

"time: point"
C3S: required
CF: recommended
latitude_longitude
height is usually 2m

"frequency":"6hr"
"level_type": "surface"
"modeling_realm":"atmos"

height is usually 2m
height:valid_min = 1.;
height:valid_max = 10. ;

tasmax leadtime
tasmaxtime
,lat,lon air_temperature "Daily Maximum Near-Surface Air Temperature" K
"reftime realization time leadtime height
time
lat lon"
"
time
leadtime: maximum (interval: <value> <unit>
)"
C3S: interval is required.
CF: interval is optional
)"
C3S: interval is required.
CF: interval is optional

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"
height is usually 2m
height:valid_min = 1.;
height:valid_max = 10. ;
latitude_longitudeheight is usually 2m
C3S: The interval is required to have a value<=3 hours)
leadtime_bnds, time_bnds are required
tasmin
time
leadtime,lat,lon air_temperature "Daily Minimum Near-Surface Air Temperature" K
"reftime realization time leadtime height
time
lat lon"
"
time
leadtime: minimum (interval: <value> <unit>)"
C3S: interval is required.
CF: interval is optional
latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"
height is usually 2m
height:valid_min = 1.;
height:valid_max = 10. ;
C3S: The interval is required to have a value<=3 hours)
leadtime_bnds, time_bnds are required
tdps
time
leadtime,lat,lon dew_point_temperature "2m
dewpoint temperature"K"height time lat lon""time: point"
C3S: required
CF: recommended latitude_longitude
Dewpoint Temperature" K "reftime realization time leadtime height lat lon" "leadtime: point"

C3S: required
CF: recommended

"frequency":"6hr"
"level_type": "surface"
"modeling_realm":"atmos"
height is usually 2m
height:valid_min = 1.;
height:valid_max = 10. ;
height is usually 2m

uas
time
leadtime,lat,lon x_wind Eastward Near-Surface Wind m s-1 "reftime realization time leadtime height
time
lat lon" "
time
leadtime: point"

C3S: required
CF: recommended
latitude_longitude

"frequency":"6hr"
"level_type": "surface"
"modeling_realm":"atmos"
height is usually 10m

height:valid_min = 1.;
height:valid_max = 30. ;
vas
time
leadtime,lat,lon y_wind Northward Near-Surface Wind m s-1 "reftime realization time leadtime height
time
lat lon" "leadtime: point"

C3S: required
CF: recommended
latitude_longitude
height is usually 10m
wsgmax

"frequency":"6hr"
"level_type": "surface"
"modeling_realm":"atmos"
height is usually 10m
height:valid_min = 1.;
height:valid_max = 30. ;

wsgmax

N/A in CMIP
time
leadtime,lat,lon wind_speed_of_gust
"Maximum Wind Speed of Gust"

N/A in CMIP
m s-1 "reftime realization time leadtime height
time
lat lon" "leadtime: maximum (interval: <value> <unit>)"
C3S: interval is required.
CF: interval is optional

latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"
height is usually 10m
height:valid_min = 1.;
height:valid_max = 30. ;

C3S: The interval is required to have a value<=3 hours)
...
leadtime_bnds, time_bnds are required

Surface Fields (not defined at a height level

...

)

attributes

name (CMIP5/6&C3S)	dimensions	standard_name	long_name (CMIP5/6&C3S)	units

coordinatescell_methodsgrid_mappingNOTESpsl

	coordinates	cell_methods	valid_min	valid_max	global attributes	Comments
psl	leadtime,lat,lon	air_pressure_at_sea_level	"Sea Level Pressure"	Pa	"reftime realization time leadtime lat lon"	"leadtime: point" C3S: required CF: recommended			"frequency":"6hr" "level_type": "surface" "modeling_realm":"atmos"
clt	leadtime

time

,lat,lon

air

cloud_

pressure_at_sea_level"Sea Level Pressure"Pa

area_fraction

"Total Cloud Fraction"

1

"reftime realization time leadtime lat lon"

"lead

"

time: point"

C3S: required
CF: recommended

latitude_longitude

		"frequency":"6hr" "level_type": "surface" "modeling_realm":"atmos"
tsl	leadtime

clttime

,lat,lon

cloud

soil_

area_fraction

temperature

"

Total Cloud Fraction

Temperature of Soil"

1

K	"reftime realization time leadtime lat lon"

"leadtime: point"

C3S: required
CF: recommended

latitude_longitude

			"frequency":"6hr" "level_type": "surface" "modeling_realm":"land"
tso	leadtime

tsltime

,lat,lon

soil

sea_surface_temperature

"Sea Surface Temperature

of Soil

"

K

"reftime realization time leadtime lat lon"

"leadtime: point"

C3S: required
CF: recommended

latitude_longitude tso

"frequency":"6hr"
"level_type": "surface"
"modeling_realm":"ocean"

sitemptop

N/A in CMIP

leadtime

time

,lat,lon

sea_

surface

ice_temperature

"

Sea

Surface Temperature of Sea Ice"

N/A in CMIP

K

"reftime realization time leadtime lat lon"

"leadtime: point"

C3S: required
CF

: recommended

: recommended			"frequency":"6hr" "level_type": "surface" "modeling_realm":"seaIce"
sic	leadtime

latitude_longitude

sitemptop

N/A in CMIP

time

,lat,lon

sea_ice_area_

temperature

fraction

"

Surface temperature of sea ice"

N/A in CMIP

Sea Ice Area Fraction"

1

"reftime realization time leadtime lat lon"

"lead

K "

time: point"

C3S: required
CF: recommended

latitude_longitude sic

"frequency":"day"
"level_type": "surface"
"modeling_realm":"seaIce"

mrlsl

leadtime,depth

time

,lat,lon

sea

moisture_content_

ice

of_

area

soil_

fraction

layer

"

Sea Ice Area Fraction"1

Water Content per Unit Area of Soil Layers"

kg m^-2

"reftime realization time leadtime depth lat lon"

"lead

"

time: point"

C3S: required
CF: recommended

latitude_longitude

		"frequency":"day" "level_type": "soil" "modeling_realm":"land"
lwesnw

N/A in CMIP

time

leadtime,

depth,

lat,lon

mass

lwe_

content

thickness_of_

water

surface_

in

snow_

soil_layer

amount

"Liquid Water Equivalent Thickness of Surface Snow Amount"

N/A in CMIP

kg

m

^-2 latitude_longitude

lwesnw

"reftime realization time leadtime lat lon"

"leadtime: point"

C3S: required
CF: recommended

"frequency":"day"
"level_type": "surface"
"modeling_realm":"land"

rhosn

N/A in CMIP

time

leadtime,lat,lon

lwe_thickness_of_surface_

snow_

amount"Liquid Water Equivalent of Surface Snow Amount

density

"Snow Density"

N/A in CMIP

kg m

^-3	"reftime realization time leadtime lat lon"

rhosn

"leadtime: point"

C3S: required
CF: recommended

latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"land"

lweprs

N/A in CMIP

time

leadtime,lat,lon

snow_density

"Snow density"

lwe_thickness_of_stratiform_precipitation_amount

"Liquid Water Equivalent Thickness of Stratiform Precipitation Amount"

N/A in CMIP

kg m^-3 "time: point"
C3S: required
CF: recommended

m	"reftime realization time leadtime lat lon"	"leadtime: sum"			"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
lweprc

latitude_longitude

lweprs

N/A in CMIP

time

leadtime,lat,lon

lwe_thickness_of_

stratiform

convective_precipitation_amount

"Liquid Water Equivalent Thickness of

Stratiform

Convective Precipitation Amount"

N/A in CMIP

m

"reftime realization time leadtime lat lon"

"leadtime: sum"

"frequency"

time

:

sum

"day"

C3S: required
CF: recommended

"level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
lwepr

latitude_longitude

lweprc

N/A in CMIP

time

leadtime,lat,lon

lwe_thickness_of

_convective

_precipitation_amount

"Liquid Water Equivalent Thickness of

Convective

Total Precipitation Amount"

N/A in CMIP

m

latitude_longitude

lwepr

"reftime realization time leadtime lat lon"

"leadtime: sum"

C3S: required
CF: recommended

			"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
lweprsn

N/A in CMIP

time

leadtime,lat,lon

lwe_thickness_of_

precipitation

snowfall_amount

"Liquid Water Equivalent Thickness of

Total Precipitation

Snowfall Amount"

N/A in CMIP

m

"reftime realization time leadtime lat lon"

"leadtime: sum"

C3S: required

CF: recommended

		"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
hfss	leadtime

latitude_longitude lweprsn

N/A in CMIP

time

,lat,lon

lwe

surface_

thickness

upward_

of

sensible_

snowfall

heat_

amount

flux

"

Liquid Water Equivalent of Snowfall Amount"

N/A in CMIP

m "time: sum"
C3S: required
CF: recommended
latitude_longitude hfss

Surface Upward Sensible Heat Flux"	W m^-2	"reftime realization time leadtime lat lon"	"leadtime: mean (interval: <value> <unit>)" C3S: interval is required. CF: interval is optional			"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
hfls	leadtime

time

,lat,lon

surface_upward_

sensible

latent_heat_flux

"Surface Upward

Sensible

Latent Heat Flux"

W m^-2

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.

CF: interval is optionallatitude_longitude

CF: interval is optional			"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
rsds	leadtime

hflstime

,lat,lon

surface_

upward

downwelling_shortwave_

latent

flux_

heat

in_

flux

air

"Surface

Upward Latent Heat Flux

Downwelling Shortwave Radiation"

W m^-2

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF: interval

is optionallatitude_longitude rsds

is optional			"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
rlds	leadtime

time

,lat,lon

surface_downwelling_

shortwave

longwave_flux_in_air

"Surface Downwelling

Shortwave

Longwave Radiation"

W m^-2

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF: interval is optional

latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"

leadtime_bnds, time_bnds are required

rss

time

leadtime,lat,lon

surface_net_downward_shortwave_flux

"Net Shortwave Surface Radiation"

W m^-2

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF: interval is optional

latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"

leadtime_bnds, time_bnds are required

rls

time

leadtime,lat,lon

surface_net_downward_longwave_flux

"Net Longwave Surface Radiation"

W m^-2

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF

: interval is optionallatitude_longitude

rst

: interval is optional

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"

leadtime_bnds, time_bnds are required

rst

N/A in CMIP

time

leadtime,lat,lon

toa_net_downward_shortwave_flux

"TOA Net Shortwave Radiation"

N/A in CMIP

W m^-2

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF: interval is optional

			"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
rlt

latitude_longitude

rlt

N/A in CMIP

time

leadtime,lat,lon

toa_net_downward_longwave_flux

"TOA Net Longwave Radiation"

N/A in CMIP

W m^-

2

²	"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is r equired.
CF: interval is optional

latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"

leadtime_bnds, time_bnds are required

rsdt

time

leadtime,lat,lon

toa_incoming_shortwave_flux

"TOA Incident Shortwave Radiation"

W m^-2

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF: interval is optionallatitude_longitude

C3S: interval is required. CF: interval is optional			"frequency":"day" "level_type": "surface" "modeling_realm":"atmos"	leadtime_bnds, time_bnds are required
tauu	leadtime

tauutime

,lat,lon

surface_downward_eastward_stress

"Surface Downward Eastward Wind Stress"

Pa

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF: interval is optional

latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"

leadtime_bnds, time_bnds are required

tauv

time

leadtime,lat,lon

surface_downward_northward_stress

"Surface Downward Northward Wind Stress"

Pa

"reftime realization time leadtime lat lon"

"leadtime: mean (interval: <value> <unit>)"

C3S: interval is required.
CF: interval is optional

latitude_longitude

"frequency":"day"
"level_type": "surface"
"modeling_realm":"atmos"

leadtime_bnds, time_bnds are required

lwee

N/A in CMIP

time

leadtime,lat,lon

lwe_thickness_of_water_evaporation_amount

"Liquid Water Equivalent Thickness of Evaporation Amount"

N/A in CMIP

m

"time: sum"
C3S: required
CF: recommended

"reftime realization time leadtime lat lon"	"leadtime: sum"			"frequency":"day" "level_type": "surface" "modeling_realm":"land"	leadtime_bnds, time_bnds are required
mrroa

latitude_longitude

N/A in CMIP

time

leadtime,lat,lon

runoff_amount

"Total Run-off Amount"

N/A in CMIP

kg m^-2

latitude_longitude

"reftime realization time leadtime lat lon"

"leadtime: sum"

C3S: required
CF: recommended

			"frequency":"day" "level_type": "surface" "modeling_realm":"land"	leadtime_bnds, time_bnds are required
mrroas

N/A in CMIP

time

leadtime,lat,lon

surface_runoff_amount

"Surface Run-off Amount"

N/A in CMIP

kg m^-2

"reftime realization time leadtime lat lon"

"leadtime: sum"

C3S: required
CF: recommended

		"frequency":"day" "level_type": "surface" "modeling_realm":"land"	leadtime_bnds, time_bnds are required
mrroab

latitude_longitude

N/A in CMIP

time

leadtime,lat,lon

subsurface_runoff_amount

"Subsurface Run-off Amount"

N/A in CMIP

kg m^-2

"reftime realization time leadtime lat lon"

"leadtime: sum"

C3S: required
CF: recommended

"frequency":"day"
"level_type": "surface"
"modeling_realm":"land"

leadtime_bnds, time_bnds are required

latitude_longitude

Pressure Level Fields

...

attributes
name
(CMIP5) dimensions standard_name long_name
(CMIP5) units coordinates cell_methods valid_min gridvalid_mappingmax NOTESglobal attributes
zg timeleadtime,plev,lat,lon geopotential_height "Geopotential Height" m "reftime realization time leadtime plev lat lon" "leadtime: point"

C3S: required
CF: recommended
latitude_longitude

"frequency":"12hr"
"level_type": "pressure"
"modeling_realm":"atmos"
ta timeleadtime,plev,lat,lon air_temperature "Air Temperature" K "reftime realization time leadtime plev lat lon" "leadtime: point"

C3S: required
CF: recommended
latitude_longitude

"frequency":"12hr"
"level_type": "pressure"
"modeling_realm":"atmos"
hus timeleadtime,plev,lat,lon specific_humidity "Specific Humidity" 1 "reftime realization time leadtime plev lat lon" "leadtime: point"

C3S: required
CF: recommended
latitude_longitude

"frequency":"12hr"
"level_type": "pressure"
"modeling_realm":"atmos"
rv
N/A in CMIP
timeleadtime,plev,lat,lon atmosphere_relative_vorticity
"Relative Vorticity"
N/A in CMIP
s^-1 "reftime realization time leadtime plev lat lon" "leadtime: point"
C3S: required
CF: recommended
latitude_longitude "

C3S: required
CF: recommended

"frequency":"12hr"
"level_type": "pressure"
"modeling_realm":"atmos"
wnddiv
N/A in CMIP
timeleadtime,plev,lat,lon divergence_of_wind
"Divergence of Wind"
N/A in CMIP
s^-1 "reftime realization time leadtime plev lat lon" "leadtime: point"

C3S: required
CF: recommended
latitude_longitude

"frequency":"12hr"
"level_type": "pressure"
"modeling_realm":"atmos"
ua timeleadtime,plev,lat,lon x_wind "Eastward Wind" m s^-1 ¹ "reftime realization time leadtime plev lat lon" "lead"time: point"

C3S: required
CF: recommended
latitude_longitude

"frequency":"12hr"
"level_type": "pressure"
"modeling_realm":"atmos"
va timeleadtime,plev,lat,lon y_wind "Northward Wind" m s^-1 "reftime realization time leadtime plev lat lon" "leadtime: point"

C3S: required
CF: recommended
latitude_longitude

...

"frequency":"12hr"
"level_type": "pressure"
"modeling_realm":"atmos"

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Key

Introduction

Examples

Encoding Guide for netCDF files conforming to C3S-0.1

Global attributes

Spatial Coordinates

Time Coordinates

Cell boundaries

Spatial Coordinates

Time Coordinates

Cell boundaries

Grid mapping

Variables

Common attributes

Conditional attributes

Candidate attributes

Static Fields

Grid mapping

Variables

Static Fields

Surface Fields (defined at a given height level)

Surface Fields (not defined at a height level

)

Pressure Level Fields

name (CMIP5)	dimensions	standard_name	long_name (CMIP5)	units	coordinates	cell_methods	valid_min	gridvalid_mappingmax	NOTESglobal attributes
		attributes
zg	timeleadtime,plev,lat,lon	geopotential_height	"Geopotential Height"	m	"reftime realization time leadtime plev lat lon"	"leadtime: point" C3S: required CF: recommended	latitude_longitude			"frequency":"12hr" "level_type": "pressure" "modeling_realm":"atmos"
ta	timeleadtime,plev,lat,lon	air_temperature	"Air Temperature"	K	"reftime realization time leadtime plev lat lon"	"leadtime: point" C3S: required CF: recommended	latitude_longitude			"frequency":"12hr" "level_type": "pressure" "modeling_realm":"atmos"
hus	timeleadtime,plev,lat,lon	specific_humidity	"Specific Humidity"	1	"reftime realization time leadtime plev lat lon"	"leadtime: point" C3S: required CF: recommended	latitude_longitude				"frequency":"12hr" "level_type": "pressure" "modeling_realm":"atmos"
rv N/A in CMIP	timeleadtime,plev,lat,lon	atmosphere_relative_vorticity	"Relative Vorticity" N/A in CMIP	s^-1	"reftime realization time leadtime plev lat lon"	"leadtime: point" C3S: required CF: recommended	latitude_longitude		" C3S: required CF: recommended			"frequency":"12hr" "level_type": "pressure" "modeling_realm":"atmos"
wnddiv N/A in CMIP	timeleadtime,plev,lat,lon	divergence_of_wind	"Divergence of Wind" N/A in CMIP	s^-1	"reftime realization time leadtime plev lat lon"	"leadtime: point" C3S: required CF: recommended	latitude_longitude			"frequency":"12hr" "level_type": "pressure" "modeling_realm":"atmos"
ua	timeleadtime,plev,lat,lon	x_wind	"Eastward Wind"	m s^-1		¹	"reftime realization time leadtime plev lat lon"	"lead"time: point" C3S: required CF: recommended	latitude_longitude			"frequency":"12hr" "level_type": "pressure" "modeling_realm":"atmos"
va	timeleadtime,plev,lat,lon	y_wind	"Northward Wind"	m s^-1	"reftime realization time leadtime plev lat lon"	"leadtime: point" C3S: required CF: recommended	latitude_longitude

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Versions Compared

Old Version 32

New Version Current

Key

Introduction

Examples

Encoding Guide for netCDF files conforming to C3S-0.1

Global attributes

Spatial Coordinates

Time Coordinates

Cell boundaries

Spatial Coordinates

Time Coordinates

Cell boundaries

Grid mapping

Variables

Common attributes

Conditional attributes

Candidate attributes

Static Fields

Grid mapping

Variables

Static Fields

Surface Fields (defined at a given height level)

Surface Fields (not defined at a height level

)

Pressure Level Fields