McIDAS-V Support Forums

When I using data downloaded from http://nomad1.ncep.noaa.gov/cgi-bin/ftp2u_gfs_dir.sh the KIndex formula work fine, but when I try with data from http://nomads.ncep.noaa.gov/cgi-bin/filter_gfs_hd.pl no work.
The formula I use for KINDEX is:
make2D(getSliceAtLevel(T, 850)) - make2D(getSliceAtLevel(T, 500)) + make2D(getSliceAtLevel(TD,850)) - ( make2D(getSliceAtLevel(T,700)) - make2D(getSliceAtLevel(TD,700)) )-273.16
Any ideas?
Many thanks for help

Cloudy

Hi Cloudy-

I did replicate your problem with the grib2 data. I believe it's because the level units in the grb2f file are in Pa, and not in hPa like the grbf file.

I made a KINDEX_grb2f formula like this:

make2D(getSliceAtLevel(T, 85000)) - make2D(getSliceAtLevel(T, 50000)) + make2D(getSliceAtLevel(TD,85000)) - ( make2D(getSliceAtLevel(T,70000)) - make2D(getSliceAtLevel(TD,70000)))-273.16

This formula works with the grb2f data. Try this and if you still encounter problems, let us know.

Thanks, Jay
McIDAS User Services

Hi Jay
Many thanks for your help. I did not know the difference between grbf and grb2f.
There are other differences in units between grbf and grb2f?
The formula works fine, thanks for your time. Cloudy

jayh wrote:Hi Cloudy-

I did replicate your problem with the grib2 data. I believe it's because the level units in the grb2f file are in Pa, and not in hPa like the grbf file.

I made a KINDEX_grb2f formula like this:

make2D(getSliceAtLevel(T, 85000)) - make2D(getSliceAtLevel(T, 50000)) + make2D(getSliceAtLevel(TD,85000)) - ( make2D(getSliceAtLevel(T,70000)) - make2D(getSliceAtLevel(TD,70000)))-273.16

This formula works with the grb2f data. Try this and if you still encounter problems, let us know.

Thanks, Jay
McIDAS User Services

Hi Cloudy-

I would suspect there may be other differences. Looking at the Field Selector and comparing the grib1 and grib2 files, there are some differences in the parameters contained in the files. hPa vs Pa for pressure levels looks to be the biggest difference, but I would check any formula carefully for each file.

Thanks, Jay

Hi Jay
I will also inform if encounter some difference between grb2 and grb2f
Many thanks
Cloudy

jayh wrote:Hi Cloudy-

I would suspect there may be other differences. Looking at the Field Selector and comparing the grib1 and grib2 files, there are some differences in the parameters contained in the files. hPa vs Pa for pressure levels looks to be the biggest difference, but I would check any formula carefully for each file.

Thanks, Jay