I’m interested in the backward trajectories at the costal site Baia Terra Nova, Antarctica, for aerosol studying. As in most of the Antarctic Plateau there are mountains, and I wonder if this is the reason why the meteorological model used by HYSPLIT “sees” the Antarctic continent so high (even though it is a coastal site)? Can I obtain backward trajectories at a lower height than the model terrain height (say at sea level), and if not, can I be confident in those trajectories starting from a much higher level than the level of the site under study?

The meteorological data is a grid cell average value. In your situation there are large terrain gradients near your station and hence the average terrain for the grid cell that contains your station is very unrepresentative. Without higher spatial resolution meteorological data there is no perfect solution. Also, unfortunately, the meteorological data are archived in pressure coordinates and although the initial computed low level trajectory will be correct near the ground (because the data file contains the 10 m wind, hence the effects of surface friction are included) as soon as the trajectory moves away from the surface, the wind will correspond with its appropriate model-terrain pressure level. I would suggest that you should always run two trajectories, one from the correct station location, and one from a location just far enough away that has a sea-level terrain height. If both trajectories are nearly identical, then you will have more confidence in the results. If they are different, then that case could be discarded or subject to further analysis.

Roland Draxler