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Next: Appendix: Modifications of APL Up: Electrostatic potential patterns in Previous: Sensitivity to Model Choices

Summary

To date no technique exists for unambiguously mapping the ionospheric electric potential over the entire high-latitude convection zone. The existing methods for approximating a global solution of $\Phi$ suffer from one or more shortcomings including limited coverage of measurements, overreliance on statistical data, or uncertainties inherent in inverting indirect measurements. The continued expansion of the SuperDARN radar networks is, however, now allowing important characteristics of the global pattern to be reliably determined from direct measurements.

The addition of two HF radars in western North America has extended the region over which the six existing SuperDARN radars provide direct measurements of plasma convection in the high-latitude ionosphere. During periods when LOS Doppler data provides sufficient coverage the selection of statistical model data has little impact on the estimation of the important, large-scale properties of the convection pattern, such as $\Phi_{\sf PC}$. The resulting maps of $\Phi$ describe the global nature of ionospheric convection yet retain the smaller-scale features dictated by the local measurements.

An example period chosen for the extended coverage of radar measurements, illustrates the independence of the fitted solution of $\Phi$ on the statistical models. Using the fitting technique of Ruohoniemi and Baker [1998] with two improvements discussed in the Appendix, maps of $\Phi$ constructed with statistical models that differ greatly in character show only minor variations. During such periods $\Phi$ and $\Phi_{\sf PC}$ are largely determined by the observations alone.

An important threshold has now been reached, namely it is now possible to reliably map $\Phi$ and determine $\Phi_{\sf PC}$ using direct measurements. During the example period only seven of the eight operational radars provided measurements of the convecting ionspheric plasma. Additional measurements from the new radar in British Columbia and another currently being constructed in Alaska will only add further confidence to $\Phi$ and $\Phi_{\sf PC}$ obtained from this fitting proceedure. The product of this analysis will provide valuable checks of ionospheric quantities derived from global magnetospheric MHD models and concepts in SW-M-I coupling.


next up previous
Next: Appendix: Modifications of APL Up: Electrostatic potential patterns in Previous: Sensitivity to Model Choices


Simon Shepherd 2000-07-13