The
ability of a body of water to store heat is due primarily to
the heat capacity of its water. Water has a specific heat of
1.0 calories per gram per degree Celsius. This means that
it takes 1 calorie of heat energy to raise the temperature of
a gram of water by 1°C. For example, using the data
from Grindstone Lake on August 8, 1999 at 2 p.m. we can calculate
the heat content of the upper layer, where
heat
content = mass x specific heat x temperature (m * C * delta T )
=
(grams) x (calories/gram/degree) x (degrees °C)
And
since Mass of water = density x volume and density = 1 gram/milliliter
which = 1 kg/Liter,
Heat
content = volume x density x specific heat x temperature
(m
* C * deltaT ) = (liters x kg/Liter) x (calories/gram/degree)
x (degrees°C)
|
Layer |
Volume
(x 105 m3) |
Temperature
(average of layer)
|
Heat
(calories per layer) |
|
0-1
meters
|
21.6
|
23.6
|
50.98
x 1012
|
|
1-2
meters
|
21.4
|
23.7
|
50.72
x 1012
|
|
2-3
meters
|
20.9
|
23.7
|
49.53
x 1012
|
|
Total
(0-3 m)
|
63.9
|
|
150.9
x 1012 |
Large
bodies of water can modify the weather in their region by their
ability to store heat energy during warm periods and release
it during cooler times. For instance in Duluth, Minnesota, the
weather forecasts typically say "cooler by the lake" in
summer because the average surface temperature of the lake is
only about 10°C (50°F) then, and "warmer by the
lake" in winter because its average temperature is about
4°C (39°F) which is much warmer than the air.
We
can follow trends in the lake's "heat budget" by computing
the heat content of its layers relative to their minimum values
at 0°C. This is the subject of a specific Studying
Heat Budgets Lesson and the Investigating
Heat Budgets Lesson. Further discussion of the heat balances
of lakes can be found in standard limnology and geosciences texts
(e.g. Horne, A.J. and C.R. Goldman 1994. Limnology, 2nd edition.
McGraw-hill, Inc.).
