Trajectory model sensitivity to differences in input data and vertical transport method

 

Joyce M. Harris, Roland R. Draxler, Samuel J. Oltmans

 

2005, J. Geophys. Res., 110, D14109, doi:10.1029/2004JD005750

 

Abstract. In this study trajectory sensitivity to the input meteorological data and vertical transport method is quantified. ERA-40 and NCEP/NCAR reanalysis data sets are used to compare isentropic and kinematic 3-d tropospheric trajectories. Expanding on previous trajectory sensitivity studies, we accumulate deviation statistics for an entire year and for three geographically diverse sites. The horizontal trajectory deviations are summarized as a percentage of average distance traveled. These results allow ranking from least to greatest among the five causes of trajectory uncertainty investigated here: minor differences in computational methodology, (3-4%); time interpolation, 9-25%; vertical transport method, 18-34%; meteorological input data, 30-40%; and combined 2-way differences in vertical transport method and meteorological input data, 39-47%. Although the deviations are somewhat dependent on starting location because of the influence of meteorology, at all three sites 3-d trajectories attained higher elevations and wind speeds than isentropic trajectories. In addition, deviation statistics for 3-d trajectories exceeded those for isentropic trajectories. The reasons for this derive from variability in the supplied vertical wind field and the higher wind speeds in 3-d trajectories on the one hand, and the vertical constraints imposed by the isentropic assumption on the other.

 

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