List of requested variables

WARNING

Some modifications have been made in this page since the meeting at C3S General Assembly at Toulouse. Please check here

Introduction

The starting point for this work was the list of parameters requested in the ITT (see here). An in-depth review of this list was performed, and some modifications were proposed to the different providers to C3S seasonal activity (ECMWF, Met Office, MeteoFrance, DWD and CMCC). Additionally, it was recognised that the original list of parameters was (to a certain extent) incomplete, as it just used GRIB parameter codes to describe the variables. This was an issue, as most of the data providers are currently using (or will do in the near future) netCDF format for the files they will supply to C3S.

Taking all of that into account, a revisited list of parameters to be used by the seasonal forecasting providers has been summarized in the tables below. This includes some basic information for encoding both in GRIB and netCDF.

A more detailed information page about the encoding in netCDF will be found in the Guide to NetCDF encoding for C3S seasonal providers, and this page should be considered the definitive specification for the data files to be provided.

Already existing data streams from the providers

Due to the current characteristics of the C3S service (in its transition from the Proof-of-Concept phase to the Pre-operational phase) this list should be considered as a reference of what should be mandatory in the future provisions of data to C3S.

In this sense, there are slight differences between what is included in the list of requested variables and the content of the actual data streams' from the providers. These differences are tolerated, even they are not desirable.

Requested variables from providers

Static Data

GRIB			netCDF
name	parameter ID	units	CF standard name	canonical units
Land-sea mask	172	(0-1)	land_area_fraction	1
Geopotential	129	m² s^-2	surface_altitude	m

Surface Fields

Sub-daily data

	GRIB			netCDF
time step	name	parameter ID	units	CF standard name	canonical units
6h	2 metre temperature	167	K	air_temperature	K
6h	2 metre dewpoint temperature	168	K	dew_point_temperature	K
6h	10 metre U wind component	165	m s^-1	x_wind	m s^-1
6h	10 metre V wind component	166	m s^-1	y_wind	m s^-1
6h	Mean sea level pressure	151	Pa	air_pressure_at_sea_level	Pa
6h	Total cloud cover	164	(0-1)	cloud_area_fraction	1
6h	Soil temperature level 1	139	K	soil_temperature	K
6h	Sea surface temperature ⁽¹⁾	34	K	sea_surface_temperature	K
6h	Sea ice temperature ⁽¹⁾	500172	K	sea_ice_temperature	K

(1) For GRIB data streams, those variables can be included as a composite field with parameter ID=139

Daily instantaneous data

	GRIB			netCDF
time step	name	parameter ID	units	CF standard name	canonical units
24h	Sea-ice cover	31	(0-1)	sea_ice_area_fraction	1
24h	Volumetric soil water layer 1 ⁽²⁾	39	m³ m^-3	moisture_content_of_soil_layer ⁽²⁾	kg m^-2
24h	Volumetric soil water layer 2 ⁽²⁾	40	m³ m^-3
24h	Volumetric soil water layer 3 ⁽²⁾	41	m³ m^-3
24h	Volumetric soil water layer 4 ⁽²⁾	42	m³ m^-3
24h	Snow depth	141	m of water equivalent	lwe_thickness_of_surface_snow_amount	m
24h	Snow density	33	kg m^-3	snow_density	kg m^-3

(2) soil water content should be provided for all native model levels (so 39-42 GRIB parameter IDs just apply to ECMWF/IFS soil model)

Daily time-aggregated data (accumulations, max/min,etc)

	GRIB			netCDF
time step	name	parameter ID	units	CF standard name	canonical units
24h	Maximum temperature at 2 metres in the last 24 hours	51	K	air_temperature	K
24h	Minimum temperature at 2 metres in the last 24 hours	52	K	air_temperature	K
24h	10 metre wind gust since previous post-processing	49	m s^-1	wind_speed_of_gust	m s^-1
24h	Large-scale precipitation ⁽³⁾	142	m	lwe_thickness_of_stratiform_precipitation_amount ⁽³⁾	m
24h	Convective precipitation ⁽³⁾	143	m	lwe_thickness_of_convective_precipitation_amount ⁽³⁾	m
24h	Total precipitation	228	m	lwe_thickness_of_precipitation_amount	m
24h	Snowfall	144	m of water equivalent	lwe_thickness_of_snowfall_amount	m
24h	Surface sensible heat flux	146	J m^-2	surface_upward_sensible_heat_flux	W m^-2
24h	Surface latent heat flux	147	J m^-2	surface_upward_latent_heat_flux	W m^-2
24h	Surface solar radiation downwards	169	J m^-2	surface_downwelling_shortwave_flux_in_air	W m^-2
24h	Surface thermal radiation downwards	175	J m^-2	surface_downwelling_longwave_flux_in_air	W m^-2
24h	Surface net solar radiation	176	J m^-2	surface_net_downward_shortwave_flux	W m^-2
24h	Surface net thermal radiation	177	J m^-2	surface_net_downward_longwave_flux	W m^-2
24h	Top net solar radiation	178	J m^-2	toa_net_downward_shortwave_flux	W m^-2
24h	Top incoming solar radiation	174089	J m^-2	toa_incoming_shortwave_flux	W m^-2
24h	Top net thermal radiation	179	J m^-2	toa_net_downward_longwave_flux	W m^-2
24h	Eastward turbulent surface stress	180	N m^-2 s	surface_downward_eastward_stress	Pa
24h	Northward turbulent surface stress	181	N m^-2 s	surface_downward_northward_stress	Pa
24h	Evaporation	182	m of water equivalent	lwe_thickness_of_water_evaporation_amount	m
24h	Runoff ⁽⁴⁾	205	m	runoff_amount ⁽⁴⁾	kg m^-2
24h	Surface runoff	8	m	surface_runoff_amount	kg m^-2
24h	Sub-surface runoff	9	m	subsurface_runoff_amount	kg m^-2

(3) Large-scale and convective precipitation are not required if total precipitation is provided (and viceversa)
(4) Runoff is not required if both surface and sub-surface runoff are provided (and viceversa)

NOTES:

Accumulations in GRIB are made from the beginning of the forecast, while in netCDF they are made accordingly to the description contained in the cell bounds/methods
In netCDF, cell bounds and methods are also used to appropriately define maximum/minimum, etc.

Pressure Levels Fields

At the following 11 pressure levels (hPa): 925, 850, 700, 500, 400, 300, 200, 100, 50, 30 and 10

	GRIB			netCDF
time step	name	parameter ID	units	CF standard name	canonical units
12h	Geopotential	129	m² s^-2	geopotential_height	m
12h	Temperature	130	K	air_temperature	K
12h	Specific humidity	133	kg kg^-1	specific_humidity	1
12h	Vorticity (relative) (*)	138	s^-1	atmosphere_relative_vorticity (*)	s^-1
12h	Divergence (*)	155	s^-1	divergence_of_wind (*)	s^-1
12h	U component of wind	131	m s^-1	x_wind	m s^-1
12h	V component of wind	132	m s^-1	y_wind	m s^-1

(*) Vorticity and divergence are not required if U and V are provided (and viceversa)

* Comment from MeteoFrance (Constantin Ardilouze) about soil moisture

I am quite aware of this issue since I have recently worked on a multi-model comparison involving the soil moisture component. In our view, only the root zone soil moisture is relevant since the deeper soil moisture is not directly available for evapotransiration.

We suggest that everybody provides the Soil Wetness Index (SWI) of the root zone which is computed as SWI=(WaterContent(root)-WiltingPoint(root))/(FieldCapacity(root)-WiltingPoint(root)). SWI does allow inter-model comparison. We can provide "SWI" as well as the "root zone depth" (in m) and the "root zone water content" (in m3/m3). However, we cannot provide the wilting point and field capacity of the root zone, because this root zone is composed of a variable number of soil layers, each of them having its own wilting point and field capacity.

In addition to SWI, root zone depth and root zone water content, we can also provide - if you decide so - the total soil water content (in m3/m3 or in kg/m2) + total soil depth (both must come together). But again, these two fields seem less relevant to us because they do not tell much about the soil water that can potentially affect the climate through evapotranspiration.

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