Earth's Atmosphere

Read this interesting article.

- structure of the earth's atmosphere
- important elements (gases) in the atmosphere.

For Vietnamese terms pls view this page about "Cac tang khi quyen"
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Scientists imagine earth’s atmosphere as an “ocean” of air hundreds of mile deep


The atmosphere of the earth exerts a lot of pressure, about 14.7 pounds per a square inch. This is normally referred to as atmospheric pressure. The air is composed of a mixture of several gases. Nitrogen is the most abundant followed by oxygen. Next to oxygen we have argon then carbon dioxide. After carbon dioxide is the “other” gases but I wont go into detail about those ones. Mixed in with theses gases is water vapor, which is the gaseous form of water. There are several important ingredients in the atmosphere. First there is oxygen, which is vital to human life, and then there is carbon dioxide, which is important to plants. Also there is water vapor in the air, which gives us precipitation, and also with the help of carbon dioxide it traps the heat of the sun within the atmosphere giving the earth a milder and more stable climate. The atmosphere is divided into to section based on the make-up. The two sections are the lower and the upper atmosphere. The lower atmosphere is referred to as the homosphere because it has a uniform mixture of gases. The upper layer of the atmosphere is referred to as the heterosphere because it has several layers of different gases. The atmosphere can be divided into several specific layers by density and temperature. The lowest layer of the atmosphere is called the troposphere also known as the “weather layer”. Next comes the tropopause, which is the upper boundary of the troposphere. The next layer is the stratosphere also called the jet stream because of its strong’ but steady winds with little or no change of weather. Above the stratosphere is the stratopause. In the stratopause lies the ozone layer, which protects the earth from the suns dangerous UV radiation. There are 3 types of radiation: first there is UVC, which is the most powerful and dangerous yet all of it is absorbed in the ozone layer. Next is UVB this type of radiation causes tanning and sunburn most but not all of it is absorbed by the ozone layer. Last but not least is UVA the least harmful and all it passes through the ozone layer with no trouble at all. Right above the ozone layer is the mesosphere, and above the mesosphere is the mesopause the mesopause is the coldest point in the atmosphere and averages to about negative 101-110 degrees Celsius (negative 150-165 degrees Fahrenheit) After the mesopause the temperature rises very quickly. The next layer in the atmosphere is the thermosphere named for its high temperature. Within the thermosphere and the mesosphere is the ionosphere and it is named that way because it is composed of many ions. Also in this same region the auroras occur they are known as the northern lights in the north and in the south the southern lights. After the thermosphere is the thermopause, which is the outer most boundary of the thermosphere. Last is the exosphere, which is the outermost layer of the atmosphere.

Heat or thermal energy that is absorbed differs from place to place. This so called heat from the sun is solar radiation. The solar radiation that reaches the earth is called insolation meaning incoming solar radiation. Our earth only receives about 47% of the suns solar radiation the rest is either reflected (37%) or absorbed by the atmosphere (18%). There are several factors affecting the earth’s insolation. First is cloudy weather because clouds are very reflective. Second is the length of daytime. Less daytime hours mean less insolation for the earth. Third is the angle of the sun’s rays. The more slanted the rays of the sun the longer it takes to heat up the earth. Last is the earth distance from the sun. When the earth is at perihelion, the closest point to the sun. It receives more insolation, but when it is at aphelion, the farthest point from the sun. The earth receives less insolation. The sun’s energy that enters the earth’s atmosphere is called the energy budget. This “energy” heats the land, water, and air.

So how does the earth contain this thermal energy? It is called the greenhouse effect. The water vapor and the carbon dioxide let the insolation in but they don’t let it escape out like the glass windows of a greenhouse. The thermal energy that the earth and its atmosphere receive from the sun is distributed several ways. One reason is because the land warms much faster then bodies of water and also the land cools faster then the bodies of water. Heat is distributed by radiation, which is heat transferred by electromagnetic waves, conduction which is direct contact between two objects, and also convection, which is the transfer of heat by moving currents of hot air, or fluids also called convection waves. Also winds are formed from convection. When rising air’s temperature heats up it’s compressed but does not have a heat loss this is called adiabatic heating; if there is no heat added and the temperature of the air-cools as it expands this is called adiabatic cooling So when masses of air rise, its temperature drops and as it sinks it heats back over and the process of cooling and heating are started over and over again.

When there is a higher than normal concentration of heat it will produce convection currents of rising air creating a low pressure called a low. If there is lower than normal heat concentration it will produce currents of sinking air creating a high pressure called a high. The way the earth rotates and causes changes in the course of the winds is called the Coriolis effect. It can be explained by two combined factors. First inertia the resistance to change in speed or direction keeps the winds in the same condition of motion. Second objects on earth’s rotating surface travel at different speeds. This causes two types of rotating winds. One is the cyclone this happens when the winds form a circulating spiral around the low. Second is the anticyclone this happens when winds form a wind system around a high. There are several wind zones in the earth. First there is the Intertropical Convergence Zone (ITCZ) this is where the winds of both the Northern and Southern hemisphere converge and rise. The next wind zone is the doldrums here there is little or periods of no wind and back then in the days of sailing vessels this was bad. Next comes the horse latitudes they are located about 30 degrees at both north and south latitudes. After the horse latitudes come the trade winds these winds blow toward the equator from the high-pressure regions of the horse latitudes.

Next come the polar easterlies these winds blow out of the northeast in the Northern Hemisphere and out of the southeast in the Southern Hemisphere together they make the polar easterlies. Another wind zone is the prevailing westerlies these winds come out of the southwest or the northwest. Last there is the jet stream these are high altitude winds concentrated in narrow, meandering bands of rapidly moving air that come mostly out of the west but it can come from all directions. Winds are normally named from the direction they come. There are also a few local winds. One is the monsoon or monsoon effect, which is when the winds reverse their direction from season to season. There is also the sea and land breeze the sea breeze brings cool air to the land during the day and at night it brings warm air to the land. The land breeze brings warm air farther inland during the day and at night it brings cool air further inland. Last is the mountain and valley breeze. During the day the cool mountain air warms as it travels to the valley and heats it. At night the warm valley air-cools and travels up the mountain and warms it.