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Name: Rony
Status: student
Grade: 9-12
Location: NY
Country: N/A
Date: 3/24/2005


Question:
How does the length of daylight affect maximum temperature?


Replies:
The longer the day, the longer the time a particular region of the Earth is exposed. However, the problem is much more complicated for several reasons:

1 The angle of the region of the Earth's orientation alters the amount of light striking that area. The maximum is when the region is perpendicular the Sun; the minimum is when the area is almost parallel to the Sun and the light just grazes the surface.

2 Cloud cover is very important since it scatters the sunlight and prevents most of it from reaching the Earth's surface. Dust, and various aerosols also scatter or absorb light, preventing it from reaching the Earth's surface.

3. Not all (or possibly even most) of the light that hits the Earth's surface goes to heating the surface. A significant amount is converted to chemical energy by photosynthesis reactions in plants (from pine trees to plankton). There are also chemical reactions that use the sunlight that prevents it from heating the Earth directly. One example is the conversion of oxygen to ozone.

4 A portion is reflected back into space and that also does not contribute directly to increasing the temperature of the Earth's surface (for example the surface ice at the north and south poles). These various complicating factors are not independent, that is, they affect one another in ways that are not always straightforward.

So the question of just how does the time of exposure of a region of the Earth to the Sun is really very complicated.

Vince Calder


Rony,

The length of daylight can have a tremendous effect on the maximum temperature.

Consider two days with the same temperature at sunrise. On the longer day, more energy from the Sun reaches the ground simply because the day is longer, but also because when the days are longer the Sun reaches to a greater height in the sky (closer to the zenith) and therefore passes through less atmosphere most of the day (meaning that less energy is scattered by the atmosphere and thus that even more energy can reach the surface).

By adding more energy to the Earth's surface on the longer day, more can be released from the surface to heat the air, resulting in a higher maximum temperature on a day with more daylight than on a day with a shorter period of daylight.

David R. Cook
Atmospheric Physics and Chemistry Section
Environmental Research Division
Argonne National Laboratory


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