SAR arc statistics provide information on the seasonal and solar cycle variations in the subauroral region electron temperature peak and associated magnetospheric energy source. There are two sources of long-term (solar cycle and seasonal) variability in the magnitude of the subauroral region electron temperature peak and associated SAR arc emission intensity: (1) the neutral atmosphere and ionosphere and (2) the magnetospheric energy source. The results of this study indicate that the observed seasonal variation in SAR arc intensities can be explained reasonably well by seasonly variations in the neutral atomsphere and ionosphere. True solstice effect are unlikely to result from differences in a near-equatorial magnetospheric heat source since the same heat source supplies both the summer and the winter hemispheres at opposite ends of a common flux tube. Observed solar cycle variations in SAR arc intensity for fixed ring current strength (as represented by the Dst index) are not consistent with variations predicted solely on the basis of a solar cycle changes in the neutral atmosphere and ionosphere. A reduction of the magnetospheric heat flux by a factor of between 5 and 20 from solar maximum to solar minimum conditions is necessary to bring model electron temperatures and 6300 ¿ emission intensity into agreement with observational results for moderately disturbed conditions (Dst~-80&ggr;). The required reduction in the magnetospheric energy source with decreasing solar cycle is attributed to compositional changes in the magnetospheric plasma. ¿ American Geophysical Union 1990