The currents of Lakes Michigan and Huron / John C. Ayers.

5

One bottle of the Lake Huron releases obviously had human help in its
travel, for it "moved" from the middle of the <south shore of Manitoulin Island
to Oliphant, Ontario in 12 days. That it moved almost directly opposite to
releases at nearby points, that it would have had to make more than half the
straight-line trip against the currents, or that it would have had to travel at
anomalously high speed to have made the trip around the mid-lake eddy in 12
days were points the prankish and not-too-honest finder failed to appreciate.
WATER TEMPERATURES
Chart 9 gives the distribution of surface water temperatures on 29 June
1955, one of the days of "normal" current pattern in Lake Michigan. Chart 10
shows a similar "'normal"t surface temperature distribution on 29 June 1954 in
Lake Huron. In each of these charts the positions of eac h whole de gre e of
Centigrade temperature have been connected by lines. Each of -these lines or
isotherms should be considered as delimiting a "puddle" or band of water which
was colder on one side of the line and warmer on the other. A "VI' lying on
its side with the point to the right means "more than"; one with its point to
the left means "less than"t and should be read with the number closest to it.
Because Centigrade temperature values are not in general use -in this
country, the following table of equivalent temperatures is included:
00 C or 32.0 Fahrenheit (freezing) 150 c or 59.0 F
6 C or 42.8 F 16 C or 60.8 F
70 C or 44.6 F 17 C or 62.6 F
80 C or 46.4 F 18 C or 64.4 F
9 C or 48.2 F 19 C or 66.2 F
l O C or 50.0 F 20 C or 68.0 F
11~ C or 51.8 F 21~ C or 69.8 F
120 C or 53.6 F 22 C or 71.6 F (room temperature).130C or 55.4 F 230 C or 73.4 F
140 C or 57.2 F 240 C or 75.2 F
The charted temperatures are for late June; they increase slowly during the
summer and by late August may be as much as 40C higher in the shallower
portions of the lakes. The very cold spot in the center of Lake Huron is a
special case, it warms to about 16 0C or 60.8 0F by late Auglust when surf ace
warming cuts off a rising of cold subsurface water there.
Dashed lines on the temperature charts indicate that there is some uncertainty as to where the lines should go.
Since temperature is the primary (but not the only) factor in determining
the density of fresh water and since the distribution of density has been used
in computing the probable current pattern, the reader might be interested in
seeing the temperature distributions. Rough estimates of current direction can
be made from the fact that the warmer water -is on the observer's right whe- n
he faces in the direction that the current is going.