Isobaric trajectories

[lnguyen5]

Hi,
I've been working lately on backward trajectories. I noticed that I ran isobaric trajectories, there's a variation of the level pressure along the trajectories. Since the method used is isobaric, the level pressure should be constant isn't it ? I was wondering if there were some kind of explanation, or am I using Hysplit wrong ?
Best regard,

[glenn.rolph]

Please see the following FAQ regarding this issue:

http://www.arl.noaa.gov/faq_hg12.php