Ellipsoidal heights h' have been determined using Doppler-satellite data collected between 1971 and 1982 is nearly 800 points in North America where the height H above mean sea level is also known. The approximate geoid height N was computed for each point using Rapp's (1978) set of potential coefficients complete to degree and order 180. An estimate of the ellipsoidal height h was then obtained using h=H+N. The differences h-'-h (which numerically were less than 4.0 m) were used to form mean values of height differences for periods from 1 month to 1 year. Yearly mean values, for which the error contribution from the geoid is small owing to the geographical distribution of the points, were then studied with respect to their time dependence. A strong correlation was observed. Yearly mean (h'-h)~0.95s-86 (cm), where s is the mean smoothed sunspot number. Using this relationship as an estimate of the error in h' for the individual points due to uncompensated ionosphere effects, the standard deviation (1 sigma) of the yearly means of the differences decreased from 55 to 20 cm. A statistical test of the corrected differences showed that they can be represented as white noise at the 95% significance level.