ACCURACY OF AIR PARCEL TRAJECTORIES AS REVEALED BY OBSERVING SYSTEM SIMULATION EXPERIMENTS.

In this study, a set of observing system simulation experiments (OSSE) was carried out to investigate the uncertainties of trajectory computations. In OSSE, the results from predictive models are assumed to represent an exact description of the 'true' atmosphere at the spatial and temporal resolution of the mesoscale grid. Three-dimensional trajectories are first computed from this 'reference data set' to represent 'true' atmospheric trajectories. The model data is then degraded to mimic observations with lower temporal and spatial resolution and to simulate actual measurements routinely available from the National Weather Service. Trajectory computations are repeated and compared with the 'true' trajectories to reveal the effects of spatial and temporal resolution on the calculations. The same procedures are repeated to investigate the effects of various simplifying assumptions.