HYSPLIT Forum: hysplitbbs.arl.noaa.gov

Hey folks,

I need to calculate backward trajectories for an aerosol report in my university.

My problem is, I don't quite understand the settings for the interval to start a new trajectory. What does this actually mean and what are reasonale values
for this and the maximum amount of trajectories being generated? Depending on the interval and the amount of trajectories I get trajectories reaching farer and spreading to completely different areas. How do I know which settings are making sense?

Thank you in advance!

A trajectory is an estimation of the path of an air parcel. It is calculated using the 3-dimensional wind field with time. If the wind field is constant over the duration of your time period of interest one trajectory would be enough. However the winds at any given point are frequently changing with time and at a given time the wind at one location is usually different from that at another location. So you need to run a lot of trajectories over your time period of interest to show the effects of the change of winds in time and space. Then you could try fewer trajectories and if the get approximately the same result, then that fewer number of trajectories should be enough.