Vertical winds in the auroral and polar cusp regions

Vertical winds in the auroral thermosphere and the polar cusp during significant periods of geomagnetic activity (AE>500 gamma) are found in many instances to be upward with speeds approaching 100 ms-1 if not higher. Coordinated with this period of strong upwelling is a period of soft particle precipitation that causes major enhancement of the 630 nm emission to levels greater than 1 kR or more. While Joule heating might indeed be the root cause of this upwelling, it is interesting that the polar cusp data obtained at the KHO facility in Svalbard by the University of London SCANDI and narrow field Fabry-Perot interferometers shows that the Burnside relation fails rather badly with a scale height of the order twice the nominal value of 50 km. This is a result that should apply to the polar region if the principle of mass continuity is valid. The issue might be the inapplicability of the hydrostatic balance assumption that is invoked in the derivation of this relation. However, there is no strong evidence to suggest that this might be true. Is there some other explanation that might clear up this puzzle?