HYSPLIT Forum: hysplitbbs.arl.noaa.gov

Hi,

I am looking at the met profile for a met file with .gbl extension and I wanted to ask how the degrees for the wind direction WDIR is defined? Is zero degrees on the North-East line?

The profile also doesn't interpolate as well and for each temporal profile the file has the following line in the header file:

"Used Nearest Gird Point (X, Y) to Lat:... Lon: ..."

I wanted to know what the numbers, X and Y, in the bracket signified?

Thanks

All the meteorological wind directions are defined as true north being zero degrees (u and v components are relative to the grid). You are right that the profile program does not interpolate the data to the actual location you specify, but rather finds the nearest horizontal grid point of the data to extract the information displayed in the results. This has less effect as the resolution of the data increases, however the global reanalysis files (.gbl) have a horizontal resolution of 2.5 degrees or about (275 km) so depending on how far the location is from the nearest grid point the meteorology selected may not be representative.

The global reanalysis data also gives the variables as a function of geopotential height. Is it possible to convert this into height above ground levels or is it better to use the hypsemtric equation https://en.wikipedia.org/wiki/Hypsometric_equation to calculate the height from the pressure levels?