On the basis of the analysis of approximately 3000 high spectral resolution scans of the direct absorption of sunlight by atmospheric sodium atoms the average seasonal and diurnal variations of atomic sodium abundance in the upper atmosphere have been deduced for Madison, Wisconsin (43¿4.5'N, 80¿24.3'W). For the period 1971--1974 an average maximum abundance of 7.7¿109 atoms/cm2 was observed to occur in early March and an average minimum of 2.9¿108 atoms/cm2 in late August. The abundance at local noon relative to the abundance ¿41/2 hours away from noon averaged 2.3 for the period of January and February and between 1.3 and 1.7 for the remainder of the year, with the minimum in June. The diurnal abundance variation in the winter appears to show a correlation with snow cover, suggesting a relationship with changes in the earth's albedo.