## Back Trajectory for station above/below see level

Topics about the HYSPLIT trajectory model.
karinard
Posts: 2
Joined: April 1st, 2018, 11:39 am
Registered HYSPLIT User: No

### Back Trajectory for station above/below see level

Hello, everyone, I need your help/advice
I have a very basic question for the calculation back or forward trajectories when we use three different heights.

What happens when you put 0 m (sea level) as one of the elevations but your location is above sea level.
For example, station A is at an elevation of 990 m above sea level (or -100m below sea level)
Does the model take this hight information into account? or only the location?

Does the 3 levels of 0, 500 and 1000 (for example) will be based on the elevation from the ground level of almost 1000m, or perhaps we have to consider them when we calculated the different heights?
Does 0 will actually be 1000, 500 will be 1500, and 1000 will be 2000m or perhaps 0 is based on sea level and I should not calculate it for my 990m station.

Thank you

barbara.stunder
Posts: 278
Joined: November 9th, 2012, 4:23 pm
Registered HYSPLIT User: Yes

### Re: Back Trajectory for station above/below see level

Please see the Trajectories and Terrain section (5.3) of the Tutorial. https://ready.arl.noaa.gov/documents/Tu ... index.html
Also this post - viewtopic.php?f=27&t=1175

karinard
Posts: 2
Joined: April 1st, 2018, 11:39 am
Registered HYSPLIT User: No

### Re: Back Trajectory for station above/below see level

Thank you for the reply,
I looked at both sources but I still do not think I have an answer to my question.

Thank you

barbara.stunder
Posts: 278
Joined: November 9th, 2012, 4:23 pm
Registered HYSPLIT User: Yes

### Re: Back Trajectory for station above/below see level

If you put 0 meters above sea level but the elevation at the site is above sea level, then the near-ground level wind fields will be used to calculate the trajectory. The model default is height above ground. Can you enter the heights above ground?

On the web you can set AGL or AMSL, and also choose to show terrain height along the trajectories. You can try runs and see the difference. https://ready.arl.noaa.gov/HYSPLIT_traj.php.

If you are using the GUI, these are set in Advanced / Configuration Setup / Trajectory.

The HELP through the GUI and the "More info" on the web give useful information.