NCEP terrain height

[so6098]

Hi,

I've been running HYSPLIT with NCEP reanalysis met data. I've been outputting the terrain height along the trajectory and noticed that the terrain height is negative over much of the Southern Ocean. Does anyone know whether this terrain height is compared to mean sea level, the geoid or something else?

Thanks for your help,

[ariel.stein]

Can you please be more specific about the meteorological data?

[so6098]

Its the NCEP/NCAR Reanalysis (1948 - present) that is available through the HYSPLIT website (link below)


http://ready.arl.noaa.gov/gbl_reanalysis.php

ftp://arlftp.arlhq.noaa.gov/pub/archives/reanalysis/

[so6098]

Its the NCEP/NCAR Reanalysis (1948 - present) data, which is available throught the HYSPLIT website (link below).

THanks


http://ready.arl.noaa.gov/gbl_reanalysis.php

ftp://arlftp.arlhq.noaa.gov/pub/archives/reanalysis/

[ariel.stein]

The meteorological dataset you are using does not contain the terrain height. Therefore, HYSPLIT needs to estimate it. That is why you might see terrain values that go below zero.

[so6098]

Thank you for the fast response. Do know of a reference that explains how this is done?

Also, I was wondering if there are any other HYSPLIT compatible met datasets that do include this terrain information?

Thanks again

[ariel.stein]

The terrain is estimated using the hypsometric equation. However, to calculate its trajectory model uses a sigma terrain following vertical coordinate that has been remapped internally from the vertical coordinate of the meteorological dataset. In that way we make sure that the trajectories do not go below the surface as defined in the original meteorological dataset.
We will soon start including the terrain information in the GDAS 0.5 degree dataset.