The altitude of the nighttime aurora obtained by parallactic photography has been shown to rise with latitude poleward and equatorward of the auroral zone. Most remaining inconsistencies between various sets of height data taken between 1910 and 1970 are shown to be removed by ordering the data according to solar activity. The measure of solar activity used is the index of recurrence probability of geomagnetic activity developed by Sargent (1979). It is found that the altitude of the aurora is inversely proportional to the probability of recurrence of the geomagnetic storm. Remaining inconsistencies in the data are probably due to the disordered solar wind associated with high geomagnetic and solar activity. This suggests that the aurora ia a more direct indicator of the condition of the solar wind than was previously suspected and that far better solar-terrestrial correlations may be achieved by using measures of solar activity associated with the relatively high-speed, ordered solar wind connected with solar coronal holes.