110 U. S. COAST AND GEODETIC SURVEY 
Jan. Mar. May July Sept. Dec. 
Los Angeles 
Seattle 
7 
Ketchikan 
Fic. 51.—Annual variation in lower low water, Los Angeles, Seattle, and Ketchikan. 
The annual variation in lower low water pictured in Figure 51 is seen to be quite 
different from the annual variation in sea level for the same stations shown in Figures 28 
and 29. Furthermore, while the annual variation in sea level at the three stations has 
ohe maximum and one minimum, the annual variation in lower low water shows two 
distinct maxima and two distinct minima. The annual variation in sea level must 
certainly be reflected in the lower low waters, but obviously a more preponderant 
variation is present in the lower low waters. 
We can eliminate the effect of the annual variation in sea level on the lower low 
waters by subtracting the montly values of lower low water from the monthly values of 
sea level. The results for three stations are shown in Figure 52, derived from 19 years of 
observations, 1930-1948. Comparing these diagrams with the corresponding diagrams 
of Figure 51 it is clear that the annual variation in lower low water is primarily periodic. 
The fact that the minima occur in June and December at all three stations points to 
the declination of the sun as the cause. 
Two elements therefore enter into the annual variation of lower low water. There 
is, first, the variation due to changes in sea level; and this variation, as has been shown, 
depends not on the range of the tide but upon its location. Second, there is the varia- 
tion depending on the sun’s declination; and this variation, as will be seen later, varies 
with the diurnal inequality. 
