An analysis of wavelength-dependent absorption in 229 FUV spectra (1150--1950 ¿) of the Jovian north polar emissions obtained with the International Ultraviolet Explorer over the period 1978--1989 shows that the hydrocarbon optical depth in front of the auroral emission has a consistent dependence on the Jovian magnetic longitude. This variation is interpreted in two distinct ways: (1) the Jovian upper atmosphere is longitudinally homogeneous, and the variation in optical depth is due to a variation in penetration, and thus energy, of the primary particles; or (2) the energy of the primaries is longitudinally homogeneous, and it is aeronomic properties which change, most likely as a result of auroral heating. For case 1, the estimates of energy per particle for each of four particles which have been proposed as auroral primaries vary by a factor of ~1.5--3.2 as a function of magnetic longitude, depending on the identity of the particles considered; the atmospheric model-dependent energies are of the order of 14 keV for electrons, 0.4 MeV for protons, 0.4 MeV/nucleon for oxygen, and 0.3 MeV/nucleon for sulfur ions in a simple model polar atmosphere which we propose. Energy estimates for oxygen and sulfur ions fall well within limits established by Voyager measurements of the population of energetic O and S ions in the magnetosphere. For case 2, changes in atmospheric properties are modeled as a variation in the eddy diffusion coefficient K in the polar model, which covers the range from ~3¿106 to 2¿107 cm-2 s-1, consistent with expected effects of localized auroral heating. Both interpretations imply a remarkable degree of stability in the coupling of the magnetosphere and atmosphere during the period of the observations, which covers a complete solar cycle and includes the Voyager encounters with Jupiter. ¿ American Geophysical Union 1990