Geography Reference
In-Depth Information
Figure 9-6:
Land
and water have
different heat ab-
sorption capacit-
ies.
In contrast, because the lake water has a certain transparency, solar energy penetrates the surface and,
depending on the clearness of the water, spreads itself out over the depths. Also, wave action and oth-
er flow mix the upper layers of water, and thereby transport the absorbed heat away from the surface.
As a result, a much greater volume of water, compared to the beach, absorbs heat. Therefore, the tem-
perature of the lake on a sunny summer day tends to be somewhat cooler than the temperature of the
beach.
This difference has significant implications for an outing at the beach, as explained below. The same
is true regarding the tendency for mid-continent locales to have warmer summers and cooler winters
than locations by the coast.
Afternoon versus evening
Assume it's a boiling hot summer afternoon. You and some friends are on a beach blanket at Point A
on Figure 9-6. The shoreline is at Point B. You decide to take a swim. The sand is terribly hot against
your feet as you run for the water and take the plunge. That water sure feels cool!
Now assume it's 9 p.m. and you are still hanging out by the lake. The sun has gone down. The tem-
perature has cooled considerably, and the sand is now somewhat cool against your feet. Someone
suggestsyouallgoforaswimandyoudecide tojoinin,howeverreluctantly.Soyourunforthewater
and take the plunge. That water sure feels . . . warm!?
How can the same body of water that cools you off at midday warm you up at 9 p.m.? As we saw in
the discussion of Figure 9-6, the beach gets super-hot on a sunny summer because solar is absorbed
and concentrated in the top veneer of surface material. In contrast, the lake heats up more slowly
because the solar energy it absorbs is spread out over a much larger volume of matter. Thus, you ex-
perience a cooling sensation when you jump into the lake in the middle of the afternoon.
