Michael Tinnesand, associate director for academic programs at the American Chemical Society, provides the following explanation: The basic answer is that the farther away you get from the earth, the thinner the atmosphere gets. The total heat content of a system is directly related to the amount of matter present, so it is cooler at higher elevations.
The heating of the earth itself also plays a role. The planet is warmed by incoming solar energy. Some of this heat bounces off the atmosphere and never reaches the lower atmosphere, and some is re-radiated back to space. In addition, the atmosphere acts like a greenhouse to reflect some of the heat back toward the earth's surface. The model was developed from atmospheric measurements that were averaged and curve fit to produce the given equations.
The model assumes that the pressure and temperature change only with altitude. The particular model shown here was developed in the early sixties, and the curve fits are given for English units.
Curve fits are also available in metric units. The model has three zones with separate curve fits for the troposphere, the lower stratosphere, and the upper stratosphere. The troposphere runs from the surface of the Earth to 36, feet. In the troposphere, the temperature decreases linearly and the pressure decreases exponentially.
The rate of temperature decrease is called the lapse rate. For the temperature T and the pressure p , the English units curve fits for the troposphere are:. This heat radiates upward, getting less intense as altitude increases. Cross Section of the Earth's Atmosphere. Four Facts About the Stratosphere. How Does Elevation Affect Weather? How Do Air Currents Work? How to Convert hPa to Altitude. Causes for Barometric Pressure to Drop. How to Calculate a Mixing Ratio.
The first reason is gravity. Earth's gravity pulls air as close to the surface as possible. The second reason is density. As altitude increases, the amount of gas molecule s in the air decrease s—the air becomes less dense than air nearer to sea level.
This is what meteorologist s and mountaineers mean by "thin air. High-altitude locations are usually much colder than areas closer to sea level.
This is due to the low air pressure. Air expand s as it rises, and the fewer gas molecules—including nitrogen, oxygen, and carbon dioxide—have fewer chances to bump into each other. The human body reacts to high altitudes.
Decreased air pressure means that less oxygen is available for breathing. One normal effect of altitude is shortness of breath, since the lungs have to work harder to deliver oxygen to the bloodstream.
It can take days and even weeks for a body to adjust to high altitude and low air pressure. People who spend too much time in high-altitude locations risk more serious symptoms of altitude sickness. These may range from headaches and dizziness to much more serious consequence s, such as brain or lung damage.
Above about 8, meters 26, feet , the human body cannot survive at all, and starts to shut down. Mountaineers call this altitude the "death zone.
To prevent severe altitude sickness, mountaineers bring supplemental extra supplies of oxygen and limit their time in the "death zone. Different regions have different air pressures, even at the same altitude.
Factors such as climate and humidity impact local air pressure. Air pressure also decreases around the pole s. For this reason, if Mount Everest was located in the U. In astronomy , altitude has a somewhat different meaning. It describes the angle between the horizon and some point in the sky.
For example, if a star is directly overhead, its altitude is 90 degrees. If a star has just set or is just about to rise, it is right at the horizon and has an altitude of 0 degrees.
The North Star , Polaris, does not rise or set because the Earth's axis passes directly through it. It thus has a constant altitude when viewed from anywhere in the Northern Hemisphere. This makes it incredibly useful in celestial navigation.
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