Uses and Limitations of the Global Convection Mapping Software

J. Michael RUOHONIEMI
The Johns Hopkins University/Applied Physics Laboratory, USA

The APL fitting technique is increasingly in use as a way to process a set of SuperDARN velocity measurements into a global convection map. The technique essentially fits all the available line-of-sight velocity information to an expansion of the electrostatic potential in terms of spherical harmonic functions. The procedure involves a median filtering of the raw velocity data from FITACF, a mapping to a global grid consisting of equal-area cells, and the assignment of uncertainties based on the spatio-temporal variability of the velocity. The radar velocities are supplemented with data from a statistical model before fitting. In this talk we will review the range of application of the technique. Some cautionary comments are in order. It must be remembered that the fitting solution represents the optimal solution for the global convection pattern. Other techniques, or even the fitting technique modified so as to preserve more local flavor, will generally be more suitable for determining an optimal local solution. The quality of the fitting should be apprised by several methods, including examination of the differences between the measured velocities and those implied by the fitting. In general, no more processing should be performed than is necessary to highlight the effect under study, and the research conclusions ought to be insensitive to reasonable variation of the fitting parameters. We will demonstrate the significance of these points with examples.

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