Question about the GDAS1 and Reanalysis

[hanjinyoo]

I have a question about the GDAS1 and Reanalysis (CDC1) methods.

I found that the backward trajectories were different by using GDAS1 and CDC1 method at same day, same time (02:00 UTC, 26 sep 2012, lat 37.57000, 124.37000).
My question is
1) what is the difference between these two methods?
2) Why the trajectory shows difference?
3) Which one is more accurate or which one is more suited for single particle analysis and which for bulk/gaseous pollutants?

[barbara.stunder]

Why do two trajectories differ when using two different analyses meteorology datasets? The atmosphere is a continuous 3-d, varying with time, field. Gridded meteorological fields do not exactly represent the atmosphere. Changes in horizontal grid, vertical levels, time intervals, and vertical velocity all affect a single trajectory. Further, a single trajectory does not show atmospheric turbulence. The two different trajectories are implying there are uncertainties in representing the flow at that particular location and time. See the Tutorial at http://www.ready.noaa.gov/documents/Tut ... index.html.