GDAS terrain height?

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ryanxia
Posts: 17
Joined: July 1st, 2016, 1:05 pm
Registered HYSPLIT User: No

GDAS terrain height?

Post by ryanxia » July 18th, 2019, 8:52 pm

Hello,

I am using GDAS 1 deg resolution data for HYSPLIT back trajectory modeling. In the traj output, there is a column of terrain height asl. What's the resolution of this "terrain" height data? Is it also 1 deg? If so, finer scale peaks or mountains might be smoothed out. Is the elevation the same for the whole 1 degree grid?

I am curious how the terrain height is treated by HYSPLIT. I saw previous posts that NCEP/NCAR terrain height is inferred from pressure fields, not real elevation asl. I am considering to use HYSPLIT trajectory end point coordinates as input to DEM raster to read the real "elevation" from the exact coordinates. Do you caveat on this?

Best,
Ryan

barbara.stunder
Posts: 334
Joined: November 9th, 2012, 4:23 pm
Registered HYSPLIT User: Yes

Re: GDAS terrain height?

Post by barbara.stunder » July 19th, 2019, 8:31 am

All the fields in a HYSPLIT meteorology file are on the same grid, so yes, the GDAS1 terrain height is at 1 degree resolution. There is no finer resolution.

The NCEP/NCAR reanalysis archive does not have terrain height, so HYSPLIT uses the surface pressure, which is in the file, to estimate the height.

ryanxia
Posts: 17
Joined: July 1st, 2016, 1:05 pm
Registered HYSPLIT User: No

Re: GDAS terrain height?

Post by ryanxia » September 4th, 2019, 3:26 pm

Hello,

Thanks for your answer. I notice that the TERR_MSL field in trajectory file is very variable. For example, in one of my trajectory file generated from GDAS 1 degree gridded dataset, TERR_MSL was 91.5, 124.3, 188.3, 267.1, 269.9, 269.7... at 0h, -1h, -2h, -3h, -4h, -5h... even the coordinates do not change that much and are still within 1 degree grid cell. If terrain elevation in GDAS is in 1 degree resolution, is TERR_MSL in trajectory file based on interpolation between neighbouring grids?

Ryan

barbara.stunder
Posts: 334
Joined: November 9th, 2012, 4:23 pm
Registered HYSPLIT User: Yes

Re: GDAS terrain height?

Post by barbara.stunder » September 9th, 2019, 9:53 am

Yes, TERR_MSL in trajectory output is based on spatial interpolation.

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