Surface Roughness to ARL

[jhamilton]

Hi,

I want to extract surface roughness data from ecmwf and use it with hysplit. I am using the
grib2arl converion program [with a few local changes]. I cannot find any mention of
roughness in the program [e.g. boundary layer has the code PBLH, precipitation
has the code TPP6 etc but I can't find a code for surface roughness]. So I wonder how can I
use it.

Thanks
James Hamilton
Met Eireann - Ireland

[barbara.stunder]

In grib2arl, in the section that defines the constants for VGRIB0, SIG0, STYPS, STYP, VCHAR0, and CNVRT0, you can make up a 4-character ID for surface roughness and then obtain the relevant constants from an inventory of the GRIB file. For an NCEP NAM dataset, we user RGHS, 83, 0, 1, 1, 1.0, but it might be different for ECMWF.

Make sure M2DV is set equal to or greater than the number of 2D variables.

[jhamilton]

Thanks .. I will try making that modification to grib2arl.
After that do I need to change things to get hysplit to
read and use the new surface roughness ?
James Hamilton - Met Eireann

[barbara.stunder]

If you use RGHS as the identifier HYSPLIT should use it. Does your dataset have friction velocity and/or surface momentum flux?

[jhamilton]

Thanks .. I am running on pressure levels with ECMWF data. At the surface I just have
10-metre wind, 2-metre temperature, surface pressure. I also extract roughness but I
did not know how to use it. I dont have friction velocity and/or surface momentum flux.

[ariel.stein]

James,

Until now hysplit was reading the surface roughness from a file located in the bdyfiles subdirectory.

We have just modified the hysplit code so it can read the surface roughness directly from the meteorological file. Please download the latest model version from our repository.

Ariel

[jhamilton]

Thanks for the info .. I will postpone including roughness for the moment since it seems quite complicated.
James Hamilton -- Met Eireann

[ariel.stein]

It should not be complicated. The new version will look for the roughness length field in the ARL formatted meteorological file. If it finds it, it will use it. Pretty simple.
Cheers.
Ariel