Temperature Controls
Altitude
Purpose: This exercise gives you practice in determining temperature changes related to the effect of altitude.
A. If two places were located at the same latitude but at different elevations, the one at the higher elevation would be cooler.
This is assuming the other environmental factors that have an effect an air temperature are the same at both places.
Many observations over the years bear out the fact that temperature drops at an average rate of 6.0° degrees Celsius for
every 1,000 meters of altitude gained. This is called the normal environmental lapse rate. It is important to note that this is an
average. On any given day the atmospheric conditions will likely cause some variation from this average.
To determine the difference in temperature, caused by altitude, between two places, first determine the difference in
elevation. Then multiply 6.0° C by the number of thousands of meters that separate the two places. This will yield the
temperature difference. If the temperature of one of the places is known, it is possible to estimate the second location's
temperature by subtracting or adding the calculated temperature difference from the first location's temperature. It is
subtracted if the second location is at a higher elevation than the first location. It is added if the second location is at a lower
elevation than the first location. The steps are:
1.
2.
3.
4.
Determine the elevation difference between the two locations.
Divide this answer by 1,000.
Multiply by 6.0° to find the difference in temperature.
Either add or subtract the temperature difference to the temperature of the known location to find the temperature of
the unknown location.
Determine the following:
1. Colorado Springs, Colorado is located near the base of Pikes Peak. The elevation of the city is 1,881 meters. The top of
Pikes Peak is 4,301 meters. If average atmospheric conditions prevail, how much temperature drop should a hiker expect to
encounter because of the elevation differential between Colorado Springs and the top of Pikes
Peak?_____________________
2. If the temperature in Colorado Springs was 5°C, what is the temperature at the top of Pikes Peak? Consider only the
effects of the environmental lapse rate.____________________
3. The temperature at the top of Pikes Peak is -5°C. What is the temperature in Colorado Springs caused by the elevation
difference?_____________________
4. Your automobile's radiator is protected by antifreeze to -30°C. Your route includes going over Independence Pass in
Colorado which has an elevation of 3,687 meters. Before going over the pass, you stop in Salida, Colorado for fuel and the
temperature there is -22"C The elevation of Salida is 2,280 meters. Determine the temperature at the pass.
Do you think you should add some more antifreeze to your radiator? ____________________
Land-Water Distribution
Purpose: This exercise will give you an understanding of the basic characteristics of locations under a maritime influence and
continental influence.
The sun's energy will strike equally at two places at the same latitude assuming the atmospheric conditions are the same. If
one of these locations is near a large body of water and the other is hundreds of miles inland, there will likely be a seasonal
contrast in temperature between these two locations.
A. San Francisco, California (37° 45'N) and Saint Louis, Missouri (38° 40'N)are nearly the same latitude but are far different in
longitude and in environmental setting. The following are the average monthly temperature for the two cities.
Plot the above data on the graph which follows. Use a blue pencil for the San Francisco data and a red pencil for the St. Louis
data.
B. Answer the following questions:
1. The average annual temperature is calculated by adding the twelve monthly averages and dividing by 12. What is the
average annual temperature of
St. Louis? ________________
San Francisco? ________________
2. The annual range of temperature is calculated by subtracting the lowest average monthly temperature from the highest
average monthly temperature. What is the annual range of temperature for
St. Louis? ________________
3.
San Francisco? __________________
In what seasons do the maximum differences in temperature occur between these two cities.
4. Why do St. Louis and San Francisco exhibit these different temperature patterns?
WHY THE EARTH HAS SEASONS
The earth revolves completely around the sun in an elliptical path (not quite a circle) in slightly longer than 365 days (one
year). As the earth revolves around the sun, it spins on its own axis, completing one spin in 24 hours (one day). The average
distance from the earth to the sun is 150 million km (93 million mi). Because the earth's orbit is an ellipse instead of a circle,
the actual distance from the earth to the sun varies during the year. The earth comes closer to the sun in January (147 million
km) than it does in July (152 million km). (See Fig. 4.1.) From this we might conclude that our warmest weather should occur
in January and our coldest weather in July. But, in the Northern Hemisphere, we normally experience cold weather in January
when we are closer to the sun and warm weather in July when we are farther away. If nearness to the sun were the primary
cause of the seasons then, indeed, January would be warmer than July. However, nearness to the sun is only a small part of
the story.
Our seasons are regulated by the amount of solar energy received at the earth's surface. This amount is determined primarily
by the angle at which sunlight strikes the surface, and by how long the sun shines on any latitude (daylight hours). Let's look
more closely at these factors.
Radiation that strikes the earth's surface perpendicularly (directly) is much more intense than radiation that strikes the same
surface at an angle. Think of shining a flashlight straight at a wall—you get a small, circular spot of light. Now, tip the flashlight
and notice how the spot of light spreads over a larger area. The same principle holds for sunlight. Radiation striking the earth
at an angle spreads out and must heat a larger region than radiation impinging directly on the earth. Everything else being
equal, an area experiencing more direct solar rays will receive more heat than the same size area being struck by sunlight at
an angle. In addition, the more the sun's rays are slanted from the perpendicular, the more atmosphere they must penetrate.
And the more atmosphere they penetrate, the more they can be scattered and absorbed (attenuated). As a consequence,
when the sun is high in the sky, it can heat the ground to a much higher temperature than when it is low on the horizon.
The second important factor determining how warm the earth's surface becomes is the length of time the sun shines each day.
Longer daylight hours, of course, mean that more energy is available from sunlight. In a given location, more solar energy
reaches the earth's surface on a clear, long day than on a day that is clear but much shorter. Hence, more surface heating
takes place.
From a casual observation, we know that summer days have more daylight hours than winter days. Also, the noontime
summer sun is higher in the sky than is the noontime winter sun. Both of these events occur because our spinning planet is
inclined on its axis (tilted) as it revolves around the sun. As Fig. 4.3 illustrates, the angle of tilt is 23 1/2° from the perpendicular
drawn to the plane of the earth's orbit. The earth's axis points to the same direction in space all year long; thus, the Northern
Hemisphere is tilted toward the sun in summer (June), and away from the sun in winter (December).
SOLAR HEATING AND THE NOONDAY SUN
The amount of solar energy that falls on a typical American home each summer day is many times the energy needed
to heat the inside for a year. Thus, many people are turning to the sun as a clean, safe, and virtually inexhaustible
source of energy. If solar collectors are used to heat a home, they should be placed on south-facing roofs to take
maximum advantage of the energy provided. The roof itself should be constructed as nearly perpendicular to winter sun
rays as possible. To determine the proper roof angle at any latitude, we need to know how high the sun will be above
the southern horizon at noon. The noon angle of the sun can be calculated in the following manner:
1.
Determine the number of degrees between your latitude and the latitude where the sun is currently directly
overhead.
2.
Subtract the number you calculated in step 1 from 90°. This will give you the sun's elevation above the
southern horizon at noon at your latitude.
For example, suppose you live in Denver, Colorado (latitude 391/2°N), and the date is December 22. The difference
between your latitude and where the sun is currently overhead is 63° (39N2°N to 231/2°S), so the sun is 27° (90° -63°)
above the southern horizon at noon. On March 21 in Denver, the angle of the sun is 501/2° (90° -391/2°). To determine
a reasonable roof angle, we must consider the average altitude of the midwinter sun (about 39° for Denver), building
costs, and snow loads. Figure 3 illustrates that a roof constructed in Denver, Colorado, at an angle of 45° will be nearly
perpendicular to much of the winter sun's energy. Hence, the roofs of solar-heated homes in middle latitudes are
generally built at an angle between 45° and 50°
Problems and Analysis:
1.
Explain (with the aid of a diagram) why the morning sun shines brightly through a south-facing bedroom window in
December, but not in June.
2.
If the tilt of the earth were decreased to only 10°, how would this change the summer and winter temperatures in
your area? Explain, using a diagram.
3.
If the tilt of the earth increased to 40°, explain how you feel the summer and winter temperatures would change in
your area.
4.
How would the lag in daily temperature experienced over land compare to the daily temperature lag over water?
5.
Calculate the noon angle of the sun above the southern horizon at your latitude on the following dates: (a)
December 22; (b) June 22; (c) September 23; and (d) March 21.
6.
On approximately what dates will the sun be overhead at noon at latitudes: a) 10°N? b) 15°S?