Basic questions about backward trajectories

[czarnetzki]

I have some basic questions about computing backward trajectories using the online version of HYSPLIT.
1) I would like to determine the sources region(s) for air that arrives at location X at time T, specifically, “where was that air 24 hours before it arrived at X and what path did it follow?” What do I use as the Start time in the Model Run Details > Model Parameters section? Would I use T – 24 hours? (I assume the ‘Total run time’ option would be set to 24.)
2) It’s unclear to me what the “Start a new trajectory every” and “Maximum number of trajectories” options mean in the Model Run Details > Model Parameters section. Is there documentation of what I should expect to receive and how to interpret the results from these options?

[ariel.stein]

I would recommend as a starting point for you to go through our model tutorial. In particular I would start at section 4:
https://www.ready.noaa.gov/documents/Tu ... index.html

[czarnetzki]

Thank you, but I didn't see anything that specifically addresses my Start time question in the online version of the model.

[ariel.stein]

Generally, the start time of a back trajectory corresponds to the time at which the trajectory arrives at the receptor. In your example the start time will be T.