When running a back trajectory I set the geopotential height as that corresponding to what is given by the sounding for a mandatory level. A specific example would be that the 850mb level from a rawinsonde sounding has a geopotential height of 1230m AGL. I input that height using the REANALYSIS (global 1948-present) (I've also tried it using the NAM12km with the same results). What I expect is that the start point for the back trajectory would be 850mb. Instead, it is not 850mb but 821mb or some other pressure depending on the sounding when I use pressure coordinates on the vertical axis. Why is the back trajectory analysis not able to yield the start point in pressure coordinates that corresponds to the start point in height coordinates.
Thank you.
Back Trajectory
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barbara.stunder
- Posts: 451
- Joined: November 9th, 2012, 4:23 pm
- Registered HYSPLIT User: Yes
Re: Back Trajectory
First - Try 1230 MSL instead of AGL. Do you know the geopotential height is agl?
Second - A model (reanalysis, nam, etc.) will not have the exact same sounding as a radiosonde. The model inputs the radiosonde, but then does a complex analysis/initialization.
At http://www.ready.noaa.gov/READYamet.php, running the "SOUNDING" program and then see the "Sounding text and any error messages". That gives the pressure and height (msl).
Second - A model (reanalysis, nam, etc.) will not have the exact same sounding as a radiosonde. The model inputs the radiosonde, but then does a complex analysis/initialization.
At http://www.ready.noaa.gov/READYamet.php, running the "SOUNDING" program and then see the "Sounding text and any error messages". That gives the pressure and height (msl).