> Trajectories differences with differing meteorology
I am trying to better understand what the best approach is for
calculating the trajectories I need. I have mostly looked at using
the EDAS data, but it has a lot of holes in it for the period I am
interested in, so we wind up with trajectories truncated or not
calculatable. I tried to fill in the holes with the FNL data. However,
in one case when I calculated 120-hour backward trajectories from Potsdam,
NY at 1800 on April 8, 1999 using both the EDAS and FNL data bases, I found
that the EDAS data suggested the air was in the upper midwest 5 days prior,
but the FNL put it into northern Quebec. Why the difference?
Although all meteorological models use the same observations, there are
three significant differences between EDAS and FNL: horizontal, vertical,
and temporal resolution. EDAS has better resolution in all categories.
For the case you sent me I re-ran the EDAS trajectory using starting
heights of 300, 400, and 500 m agl. There are large differences in the
first 24 hours. The 400 m trajectory corresponds more with your 500 m
FNL. EDAS vertical resolution is every 25 hPa, FNL resolution is limited
to mandatory surfaces: 1000, 925, 850 hPA etc. The usual procedure should
be to run trajectories at several heights and locations about the point of
interest -- if the trajectories are similar then the confidence level is
high -- if they diverge then there is more uncertainty.