The coupling of electromagnetic energy into the ionosphere and thermosphere is an essential consideration for understanding the thermal structure and dynamics of the neutral and charged particles at high latitudes. Often the dissipated electromagnetic energy exceeds that deposited by precipitating energetic particles at high latitudes. It is usually assumed that the profile of the ion Pedersen conductivity determines the altitude dependence of the energy dissipation rate. Herein we point out the strong altitude dependence of the energy dissipation rate on the spatial scale size of the imposed electric field. To illustrate the importance of such considerations, we show examples of the ubiquity of electric field structure in the high-latitude ionosphere; this is particularly prominent when the interplanetary magnetic field has a northward component. We then show quantitatively how the existence of electric field structure with scale sizes of 10 km or less strongly impacts both the altitude extent over which the electromagnetic energy is dissipated and its partitioning between current systems perpendicular and parallel to the magnetic field. ¿American Geophysical Union 1991