Atmosphere And Weather

Factors that Affect Air Temperature



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The air temperature where you are is affected by many different things. Global effects caused by seasons and wind currents are part of the picture, but more specific things like terrain and cloud cover in a particular location also contribute to the air temperature.

The earth is tilted on its axis. As the earth orbits the sun, the tilt of the axis remains the same, so on one side of the orbit, the northern hemisphere is closer to the sun, resulting in summer there, and on the other side of the orbit, the southern hemisphere is closer to the sun, resulting in winter for the northern hemisphere. Because the equator is closest to the sun regardless of the tilt of earth's axis, the temperature fluctuates less around the equator than at any other latitude and consistent warm temperatures are found there.

There is a tendency to equilibrium in all systems, and this is what drives the movement of heat through air and water currents around the earth. At the equator, the sun is shining most directly on to the land. The tropical areas around the equator absorb much more radiant energy from the sun than they reflect. In contrast, the polar areas receive sunlight at an angle, so the light has to travel through a greater amount of atmosphere. For this reason, the polar areas absorb less heat from the sun than what they reflect.

Wind currents carry the excess heat energy from tropical areas to cooler areas around the planet. Sea currents follow the same pattern, carrying warmer water into cooler areas. A great example of this is the Gulf Stream, which moves warm water from the Caribbean and southern Atlantic up the coast of North America and into northern Atlantic waters. This constant movement of heat energy drives changing weather patterns.

Locally, temperature is affected by altitude. Higher elevations are cooler because of the change in air pressure. Compression of molecules causes heat. The higher air pressure at lower elevations results in higher air temperatures. The reverse is true at higher elevations. To illustrate, the air pressure at sea level is measured as one atmosphere, 14.7 pounds per square inch (psi). At an elevation of 18,000 feet, the air pressure is roughly half that at sea level, about 7.3 psi. All other factors being equal, the air temperature decreases about seven degrees Fahrenheit for every 2,000 feet of altitude gain. Thus a temperature of 80 degrees at sea level would be about 16 degrees at 18,000 feet.

Cloud cover affects local temperatures as well, because the clouds absorb the sunlight before it reaches the earth's surface. Other particles suspended in the air can have an impact on temperature, too. Clouds of dust from surface storms or ash from volcanic eruptions can significantly change local air temperatures. Like clouds, these particles prevent the sun's energy from reaching the surface.

Man-made structures also have a great impact on local temperatures. In large cities where there is a concentration of stone, concrete, and asphalt-covered streets, the huge amount of radiant energy absorbed by these materials makes cities much warmer than surrounding countryside. In rural areas, a large amount of the radiant energy is used to evaporate moisture from vegetation and soils, leaving less heat to warm the countryside.

These are only the most obvious factors affecting air temperature. There are many others, such as distance from the ocean, latitude, and the direction of prevailing winds. These many variable factors are the reason it is so difficult for meteorologists to produce precise weather forecasts.

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