Based on following documents:

1. New short-wave radiation parameters

Proposed parameters for Product discipline 0 - Meteorological products, parameter category 4: short-wave radiation

ParameterUnitsDescription
Downward short-wave radiation flux, clear sky
Wm-2
Downward short-wave radiation flux computed under actual atmospheric conditions but assuming zero cloudiness.
Upward short-wave radiation flux, clear sky
Wm-2
Upward short-wave radiation flux computed under actual atmospheric conditions but assuming zero cloudiness.

Question: What about "Direct short-wave radiation flux, clear sky" produced by IFS and archived in MARS under paramId 228022 (Clear-sky direct solar radiation at surface)

Justification: The proposed parameters are commonly computed by numerical weather prediction models and operationally archived. They are of the same type like ones already existing in WMO code tables (e.g. Downward short-wave radiation flux, Net short-wave radiation flux, clear sky). Additional information illustrating their meaning and handling can be checked in the attached document about radiation quantities in the IFS model developed by ECMWF.

2. New long-wave radiation parameter

 Proposed parameters for Product discipline 0 - Meteorological products, parameter category 5: long-wave radiation

ParameterUnitsDescription
Downward long-wave radiation flux, clear sky
Wm-2
Downward long-wave radiation flux computed under actual atmospheric conditions but assuming zero cloudiness.

Justification: The proposed parameters are commonly computed by numerical weather prediction models and operationally archived. They are of the same type like ones already existing in WMO code tables (e.g. Downward short-wave radiation flux, Net short-wave radiation flux, clear sky). Additional information illustrating their meaning and handling can be checked in the attached document about radiation quantities in the IFS model developed by ECMWF.

3. Soil heat flux

Proposed parameter for Product discipline 2 - Land surface products, parameter category 3: soil products

ParameterUnitsDescription
Soil heat flux
Wm-2
The soil heat flux is the energy receive by the soil to heat it per unit of surface and time. The Soil heat flux is positive when the soil receives energy (warms) and negative when the soil looses energy (cools).

Justification: The heat flux is currently defined only under Product discipline 2 - Land surface products, parameter category 0: vegetation/biomass. The currently existing parameters in the same category related to soil are mostly deprecated and moved to the category 3: soil products where the soil heat flux is not defined at all.

4. Percolation 

Proposed parameter for   Product discipline 1 - Hydrological products, parameter category 0: hydrology basic products 

ParameterUnitsDescription
Percolation rate
kgm-2s-1
The newly proposed percolation is  the downward movement of water under hydrostatic pressure in the saturated zone.This water might still end up in rivers and lakes as discharge but it is a slower process than water runoff or drainage. Such defined percolation is an input for hydrological models together with e.g. water runoff. This parameter is proposed as a rate rather than the accumulation following WMO recommendations. The accumulated value can be encoded as usually using the rate with accumulation specified in PDT.

Justification: There is only "Water runoff and drainage" defined in the WMO tables which is not suitable for this newly proposed parameter. 

Real-life example:  The newly proposed percolation rate what be the parameter K3 in the SURFEX 3-layers scheme (right picture ISBA 3-L; it is called gravitational drainage there).

5. Soil levels

Newly proposed type of level soil level for Code table 4.5-Fixed surface types and units

Type of LevelUnitsDescription
Soil level
-
This level represents a soil model level (similar to hybrid model level above surface). The scaled value encoded together with this new type of level represents the level number. The aim of this type of the level is to encode a soil level that has not a constant depth across the model domain (each grid cell has soil levels of different depths). The non-constant depth is then encoded as a parameter on this type of level alongside the other parameters like temperature, soil moisture, etc. A "soil layer" (useful to encode volume integrated parameters)  can be represented by defining 2 soil model levels using the usual GRIB2 mechanism ("first fixed surface/second fixed surface" where the deepest soil level is always encoded as the second fixed surface).
ParameterUnitsGRIB2 codeDescription
Soil depthm

discipline 2

category 3

number ??

This parameter is used to encode the soil depth in meters (The depth is positive downward by convention). It is meant to be used together with the type of level "soil level" to encode the depth of the level at each grib point.


Justification: In some models, the depth of the soil levels is not constant for all model grid points. The depths will vary depending on several factors like the type of land cover (grass, forests, crops, city, etc.), time of the year, etc. (see below for concrete examples).  It is not possible to encode soil parameters like soil temperature for such systems using the actual WMO code tables: type of level 106 - "depth below Land surface" only allows encoding of constant depth for the whole domain, types of level 167 and 177 could be useful, but only grasp 2 very specific depths and do not solve the encoding of an n-levels soil model. The newly proposed type of level "Soil level" would allow a generic encoding of these levels similarly like hybrid levels do for model levels above surface. Soil levels would be dimensionless and the level number would be encoded using scale factor/scaled value mechanism. Once a soil level is defined, one can define a parameter on that level to encode the non constant depth in meters. This is why we would like to propose a new "soil depth" parameter in "Product discipline 2 – Land surface products, parameter category 3 soil products" to be used in conjunction with the new type of level.

Real-life example: In some surface schemes like the SURFEX surface model, the depths of soil layers are not constant. SURFEX is part of Hamonie system and will be used in Arpege (part of IFS) and will also be used in the Aladin community. The depths of soil layers are computed at the beginning (during Analysis) according to several factors: type of land cover, time of the year, etc. To illustrate this lets look at the soil scheme provided in SURFEX documentation: 3-layers scheme. The key point to understand is that the values of "ds", "d2" and "d3", which are the depths corresponding to the bottom of the surface layer, bottom of root zone layer and deep soil layer are NOT the same for each grid cell. This is because an oak tree does not have the same root length like a pine which have itself a different root length than grass, etc. The time of the year has also an influence on the depth of the bottom of the root zone: early in the Spring the crops are very small and are only starting to grow for the seeds disseminated on the fields, their roots are very small. During the summer (or the harvesting season) the roots goes much deeper hence the bottom of the root zone is deeper as well to reflect that. After the fields have been harvested the root zone does not exist any more (like during the winter for instance). In case of SURFEX the information about depths of each level for each grid point are extracted from the ECOCLIMAP II database (see particularly fig1). These depths can be written by the model in GRIB messages if the appropriate type of level and soil depth parameter are defined.

How to represent soil levels.

First Layer Soil Temperature
Discipline=2
parameter Category=3
parameter Number=18
First fixed surface=151 "Soil level"
scale Factor=0
scaled Value=0
Second fixed surface=151 "Soil level"
scale Factor=0
scaled Value=1

 

Height of the soil level
Discipline=2
parameter Category=3
parameter Number=27  "Soil depth"
First fixed surface=151 "Soil level"
scale Factor=0
scaled Value=1
Second fixed surface=missing
scale Factor=missing
scaled Value=missing

 

 

11 Comments

  1. Regarding percolation, it is as you state vertical movement of water through the rock or soil (under hydrostatic pressure). This is a process, where the water is still in the soil or ground water, but leaves the active root zone and becomes "inactive" for interaction with vegetation. However, I am not sure that this is needed for the UERRA project? If what is meant is that the water is "lost" through a vertical motion, then it is OK to define this parameter. If however it has the meaning of runoff from deeper soil layers, then it si better to use the "runoff and drainage" parameter which is already defined.

    I have also modified the definition of percolation above.

     

    1. Hi Fredrik,

      I have a question regarding percolation. is it correct to have the unit as kg m-2 and not kg m-2 s-1, suggesting that percolation is instantaneous (you describe something "moving" in your comment). It can then be time integrated (accumulated over time) to produce an accumulated field with unit in kg m-2.

      1. Sebastien,

        Then we should perhaps call it "Percolation rate" to mark that it is a rate. I followed the same convention as for for example Precipitation and Runoff, which are accumulations in time (kg m-2). I am not sure when it is better to use a rate (instantaneous) and when to use accumulation.

        1. Everything depends on what most models produce. if a model produce the rate and eventually the accumulation, then we should propose "percolation rate" with units kg m-2 s-1. With that parameter we can still encode an accumulated field (like we do for precipitation) using the grib key for statistical processes "accumulation" and we obtain "percolation" with units kg m^-2. If we propose simply "percolation" with units kg m^-2, we will never be able to encode the instantaneous parameter.So Percolation rate is more flexible but I don' t know if it make sense to have it.

          I can not make a decision as I am not the researcher producing those parameters and I don' t know what will be needed in the future (we also need to take into account future needs to not be trapped with a too narrow use case).

          1. I agree, this needs more thought. I would therefore, as I previously suggested, not propose percolation as a new parameter, rather stick to "Runoff and drainage" for the UERRA project.

  2. We need descriptions for all the parameters. We also need a description for the soil layer. How the users will know in 20 years that the depth of the soil layer can be extracted from the "well known" ECOCLIMAP II database? 

  3. why do we need "Downward long-wave radiation flux, clear sky" ? On the document pointed out by Richard in the justification about the radiation scheme at ECMWF, it clearly shows that Downward long-wave radiation flux is assumed to be .. 0! However the "upward" long wave radiation flux seems significant.

    1. That is the only missing type of the long-wave radiation which models compute without WMO definition. Going to higher resolution it will not be zero any more. But for UERRA it is not on the list so it just came to my mind thinking of future and IFS planned move to GRIB2 soon completely.

  4. I think that the soil levele is complex to implement and I am afraid that we cannot do it in time for the next FT.

    If we accept the fact that aparameter as soil level 1 is something like 

    discipline=2
    category=3
    parameterNumber=18
    First fixed surface="soil level"
    scale Factor=0
    scaled Value=0
    Second fixed surface="soil level"
    scale Factor=0
    scaled Value=1
    How do we specify the depth of 
    Second fixed surface="soil level"
    scale Factor=0
    scaled Value=1
    We can say that we produce a new field with 
    discipline,category,parameterNumber="soil depth"
    First fixed surface="soil level"
    scale Factor=0
    scaled Value=1
    but this is not 100% clear as you have a field "soil depth" at level "new soil level". This needs clear explanation to say that when the "soil depth" is used in conjunction with "soil level" the field has to be considered as the depth of the mentioned soil level.
    This is not trivial.
    Enrico 
  5. Writing the proposal I remembered that I went already through the same thing with a proposal from DWD. The level type we need is already defined. This is very important because it eliminates the most difficult bit from the proposal.

    I am going to modify the page with the proper coding example.

  6. apart the fact we want to proposed "Generalised vertical depth coordinate" to mirror the already existing "Generalised vertical height coordinate", do we agree that we then need A "depth" parameter in discipline 0 category 3 or maybe in discipline 2 category 3 (similar to the water depth parameter defined in discipline 1 category 2).

    a side note: Enrico, on your example of "height" of soil level, shouldn't it be a "1" in the scaled value for the "height" of the first level? As I understand it there is no zero level for this leveltype.