EM 1110-2-1100 (Part II)
30 Apr 02
Tide predictions for Boston, MA (Harris 1981)
series shown in Figure II-5-5. Note that in Figure II-5-5, the envelope that connects higher-high tide values
for the first spring tide during the first 14.5 days becomes an envelope of the lower-high tide values during
the second spring tide.
(4) Diurnal inequality.
(a) In the above example, the envelope of two successive high or low tides defines spring and neap
conditions. Alternate tides were used because the ranges of two successive tides at a given location are
generally not identical, but exhibit differences in height. Examples are evident in Figure II-5-5. These
differences are referred to as the diurnal inequality of the tide and result from the relative position of the sun
and moon as well as the specific location of an observer on the earth.
Water Levels and Long Waves