School of Meteorology (Defense)

Improving Trajectory Analyses Using Advection Correction: Tests with a 30-m Simulation of the 24 May 2011 El Reno, OK,Supercell

Stefan Rahimi
OU School of Meteorology

01 December 2014, 9:00 AM

National Weather Center, Room 5820
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Trajectories are widely used in atmospheric science, oceanography, hydrology, and other earth sciences. In meteorology, trajectories have been used to study atmospheric chemistry, identify source regions for particular air masses, and gain kinematic/dynamical understanding into atmospheric processes. Previous studies using numerical simulation data have shown that the accuracy of traditional trajectory analyses is very sensitive to the spatial and temporal resolution of the wind field data. Specifically, trajectory errors have been shown to increase significantly as the data frequency is reduced (Kuo 1985; Doty and Perkey 1992). In this study, we show that advection correction (AC) procedures can take advantage of Taylor’s frozen turbulence hypothesis to mitigate the temporal coarseness of the data. The frozen turbulence hypothesis approximates a scalar’s evolution as being dependent only on its translation velocity components U and V. Advection correction makes use of this in the time-interpolation step, in order to more accurately represent a scalar feature in time and space. This paper will explore the suitability of advection correction in trajectory analysis in tests using low-altitude high spatio-temporal frequency numerical model data of a supercell (Orf et al. 2014). In these proof of concept tests, we restrict attention to 2-D (horizontal) trajectory analysis. For the AC experiments, the translation velocities are computed with an iterative procedure (Gal-Chen 1982) on local analysis subdomains. These advection-corrected wind data are then used to solve the two-dimensional trajectory equations. Reference trajectories are then computed using high frequency data input. Trajectories computed using traditional linear interpolation are then compared to trajectories computed using iterative and non-iterative advection correction techniques. It is shown that the AC-procedures improve trajectory accuracy, with the best improvements obtained when Gal-Chen’s iterative technique was used.

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