WMO proposals for new UERRA parameters

Based on following documents:

• 2015-10-20 Meeting notes
• UERRA parameter list

1. New short-wave radiation parameters

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

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

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

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 2 - Land surface products, parameter category 0: vegetation/biomass (???) Fredrik Wetterhall would rather suggest Discipline 1, category 0

 Justification: The newly proposed percolation is  the downward movement of water under hydrostatic pressure in the satured 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. If percolation is to the groudn water, it can also be named as ground water recharge.

5. Soil layer 

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

 Question: Instead of soil layer one could ask for soil level to achieve the same target described below. What would be the differences and pros or cons between them?  The technical differences are easy to grasp.

Justification: Currently  in some numerical weather models' surface schemes the depths of the soil layers are not constant for all model grid points but varying depending on several factors like type of land cover, time of the year etc.  It is not possible to encode soil parameters like soil temperature for such systems using the actual WMO code tables. The newly proposed type of below surface level "soil layer" would allow it similarly like for example hybrid level is used for appropriate model level data above surface. As such way defined soil layers would be dimensionless the users would have to know where, in what external source outside of grib, to search for  particular soil level depths corresponding to each grid-point and soil layer. More detailed reasoning of this new concept is below.

Real-life example: In some surface schemes like French SURFEX that is part of the HARMONIE numerical weather prediction system the depths of soil layers are not constant like in some other models e.g. IFS run by ECMWF. Those  depths of soil layers are computed 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 be 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. During the summer (or the harvesting season) the roots are much bigger hence the bottom of the root zone is deeper. 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 soil layer for each grid point can be extracted from well known ECOCLIMAP II database (see particularly fig1)