What are the levels of uncertainty associated with back trajectory calculations of ambient and potential temperature in the Hysplit model meteorological outputs? I am trying to use the model, to do 5-day backward trajectories of two air parcels (200m and 1000m) starting at my study location. I would like to use the temperature outputs to understand processes within my study region and would like to know its accuracy.

The meteorological data that are an optional output with each trajectory are valid at that trajectory position and time as interpolated from the meteorological data file used for the trajectory calculation. The question might be how representative is that value for that position. The values come from NOAA’s NCEP meteorological models, run at either 12 km (NAM) or 100 km (GFS) resolution. However, these data are interpolated to grids at coarser resolution that we use for transport and dispersion calculations. For instance, 40 or 80 km for NAM. Thermodynamic variables such as temperature are produced by the meteorological model are grid cell averages and are consistent with the equations of motion. They may not be representative of a nearby measurement. That will depend upon local effects as well as the larger scale gradients of the variable and how well a gridded field can represent a continuous function.

Roland Draxler