> How do I estimate the absolute (in km) and relative (%) errors when using
the HYSPLIT trajectory model?
How do I estimate the absolute (in km) and relative (%) errors when using
the Hysplit4 trajectory model? Where does the error mostly come from (e.g.,
truncation error, interpolation error or wind field error)?
The error is
caused by a numerical and a physical component. Overall, from the literature,
one can estimate the total error to be anywhere from 15 to 30% of the travel
distance. The physical component of the error is related to how well the
numerical fields estimate the true flow field. We have no way of knowing
this without independent verification data. The numerical component of the
error we can estimate. This error is composed of the integration error
(part of which is due to truncation) and an error due to the
data resolution - trying to represent a continuous function, the
atmospheric flow field, with gridded data points of limited resolution
in space and time. The integration error can be estimated by computing a
backward trajectory from the forward trajectory endpoint - the error is
then 1/2 the distance of the final endpoint and starting point. The
resolution error can be estimated by starting several trajectories about
the initial point (offset in the horizontal and vertical). The divergence
of these trajectories will give an estimate of the uncertainty due to
divergence in the flow field. You can use an initial offset that is comparable to
your estimated integration error. One component of the resolution error
that is difficult to estimate relates to the size and speed of movement of
various flow features through the grid. There should be sufficient number
of sampling points (in space and time) to avoid aliasing errors.