Hypothesis One: Temperature = Solar Radiation

The temperature is proportional to the solar radiation. When the sun is high, the air is hot.

What predictions can be drawn from this hypothesis? Check all that apply. Note that I am not asking you which of the statements are true; I am asking you which of the statements WOULD be true if the hypothesis were correct.

To see if this hypothesis is right, we need to know how the solar radiation changes during the day. If the solar radiation graph matches the temperature graph, the hypothesis may be correct. Below is a typical example of the solar radiation received by a patch of soil during the summer.

A graph showing the solar radiation throughout a day in the summer for a patch of soil

In this figure, the red-dashed is the maximum possible solar radiation for that day at that latitude, and the yellow-solid is the actual amount received.

Why do you think it looks like this? The part at night is obvious: the sun has set, so there's no solar radiation reaching the soil. During the day, the variation in intensity (with the peak at noon) is caused by the changing angle of the sun. There are two reasons for this. First, and most important, the lower the sun, the smaller the amount of radiation intercepted by a horizontal surface. (The earth is not completely flat, but over most areas it averages out to being nearly horizontal.) Second, the lower the sun, the greater the amount of air the sunlight has to pass through, and the more gets scattered by air molecules, by haze, and even by clouds.

Evidence in favor of hypothesis 1:

Personal experience: you feel hotter (and get a tan faster) when the sun is high.

Evidence against hypothesis 1:

The warmest temperature is not usually at midday, but later in the afternoon.
The fall of temperatures during the nighttime is unexplained.

The same graph from earlier pages showing the observed temperature and dew point at the Norman, OK observation station

So hypothesis 1 would explain why days are warm and nights are cold, but the details don't match at all. The predictions didn't come true: sure, the temperature rose in the morning, but it kept rising in the early afternoon, even though the incoming solar radiation had stabilized and started to fall. At night the temperature kept falling, even though the solar radiation was a constant (zero) all night.

Go back to the list of hypotheses and select another one.

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