EU-Confidence Case data Relevant questions

Borssele case studies

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Relevant questions

During the test phase with the Easy case, several questions popped up on the different meteorlogical parameters.

Mixing level height

The mixing level height can reach values that are very high for dispersion modelling. In the ensemble data we have limited the value to 1500m.

Roughness length

The roughness length is not included in the standard Harmonie output. We extracted a roughness-length field (times g) from one of the analyses. Over land this can be used throughout the period. Over sea the roughness length depends on the sea state, but as the plumes will not go over sea, we propose to use this fixed field anyway.

Surface height

Some of the models also need the surface height. We extracted a fixed geopotential height field (surface height times g) and included this in the ensemble data.
Over sea the same considerations hold as for the roughness length.


Precipitation (rain, snow and graupel) is provided at surface level and at hybrid levels. At surface level there are two precipitation fields. One is the one hour accumulated precipitation in kg/m², which corresponds to mm/h. For most models this is the precipitation you want. The other field is an indication of instantaneous precipitation, converted to a mm/h amount.
At the hybrid levels log(precipitation) (which can hence be negative) is given in kg/kg (kg water per kg air).

Because these different precipitation variables gave rise to some confusion, and only the accumulated preciptation at the surface is needed, we omitted the instantaneous parameters at model levels and surface in the dataset for the Borssele-2 scenario.

GRIB coded data

In the GRIB coded data the parameter number is 181 and the accumulated and instantaneous fields can be identified by the timeRangeIndicator TR which is 0 for instantaneous and 4 for accumulated quantities.

As an example for a +10 hour forecast the output of wgrib for the one hour accumulated rain is

3:361224:d=17011106:LPSX:kpds5=181:kpds6=105:kpds7=0:TR=4:P1=9:P2=10:TimeU=1:0m above gnd:9-10hr acc:NAve=0
where P1=9 is the start of the accumulation and P2=10 the end.
The instantaneous surface field will show TR=0, P1=10 and P2=0.

NetCDF data

The conversion from GRIB to NetCDF seems to have lost the information from the timeRangeIndicator.

In the NetCDF files which are provided in this project for the ensemble in the Borssele case, the variables are called rain which is the 1 hour accumulated surface rain with TR=4, rain_2 which is the rain at the hybrid levels, and rain_3 which is the instantaneous surface rain with TR=0.
In the Borssele-2 dataset this variable is called just rain.

Hans de Vries, March 12, 2019