Atmosphere Characteristics 2:The Atmosphere

Ozone

Another important variable component of the atmosphere is ozone. Ozone is a form of oxygen that combines three oxygen atoms into each molecule (O3). Ozone is not the same as the oxygen we breathe, which has two atoms per molecule (O2).

The Seasons

On June 21 or 22 each year, the axis is such that the Northern Hemisphere is "leaning" 23.5 degrees toward the sun. This date is known as the summer solstice or the first "official" day of summer.

What is ozone and how is it formed?

Ozone is a form of oxygen in which every molecule contains three atoms of oxygen. Ozone is formed when a single atom of oxygen (O) and a diatomic molecule of oxygen (O2) collide.

Ozone 3

Ozone is concentrated 10 to 50 kilometers above Earth because the UV radiation from the sun is sufficient to produce single atoms of oxygen. In addition, there are enough gas molecules to bring about the required collisions. The ozone layer is crucial to life on Earth. Ozone absorbs potentially harmful UV radiation from the sun. If ozone did not filter most UV radiation and all of the sun's UV rays reached the surface of Earth, our planet would be uninhabitable for many living organisms.

Length of Daylight

The length of daylight compared with darkness also is determined by Earth's position in orbit. All latitudes receive 12 hours of daylight during the vernal and autumnal equinoxes (equal night). The length of daylight on the summer solstice in the Northern Hemisphere is greater than the length of darkness. The farther you are north of the equator on the summer solstice, the longer the period of daylight. When you reach the Arctic Circle, at 66.5 degrees north latitude, the length of daylight is 24 hours.

How does Earth's atmosphere change with distance above the surface?

It becomes increasingly thin, eventually forming a gradual boundary with space.

Composition of the Atmosphere 2

About 3.4 billion years ago, the first photosynthetic bacteria appeared and thrived in the carbon dioxide-filled atmosphere. Oxygen, a byproduct of photosynthesis, began to accumulate in the atmosphere about 2.5 billion years ago. In the meantime, solar energy broke down ammonia molecules in the atmosphere and released nitrogen and hydrogen. The hydrogen, being the lightest element, floated to the top of the atmosphere and, eventually, out into space. Earth's current atmosphere is made up primarily of nitrogen and oxygen. Today's atmosphere continues to exchange material with the oceans and life on the Earth's surface.

Human Influence

Air pollutants are airborne particles and gases that occur in concentrations large enough to endanger the health of organisms.

stratoshpere

Beyond the tropopause is the stratosphere. In the stratosphere, the temperature remains constant to a height of about 20 kilometers. It then begins a gradual increase in temperature that continues until the stratopause, at a height of nearly 50 kilometers above Earth's surface. Temperatures increase in the stratosphere because the atmosphere's ozone is concentrated here. Ozone absorbs ultraviolet radiation from the sun. As a result, the stratosphere is heated.

Carbon Dioxide

Carbon dioxide is present in only small amounts (approximately 0.039 percent), but it is an important component of air. Carbon dioxide is an active absorber of energy given off by Earth. Therefore, it plays a significant role in heating the atmosphere.

What is the difference between weather and climate?

Climate is a description of aggregate weather conditions for an area, and weather is the state of the atmosphere at a given moment in time.

Earth's Motions

Earth has two principal motions: rotation and revolution. Rotation is the spinning of Earth about its axis. The axis is an imaginary line running through the north and south poles. Our planet rotates once every 24 hours, producing the daily cycle of daylight and darkness. Revolution is the movement of Earth in its orbit around the sun. Earth travels at nearly 113,000 kilometers per hour in an elliptical orbit about the sun.

Temperature Changes

Earth's atmosphere becomes colder as you climb higher. But not all layers of the atmosphere show this temperature pattern.

What is the main cause of seasonal changes to the weather?

Earth's changing position relative to the sun

Variable Components

Important materials that vary in the air from time to time and place to place include water vapor, dust particles, and ozone. These components also can have significant effects on weather and climate. The amount of water vapor varies from almost none to about 4 percent by volume. Why is such a small quantity so significant? Water vapor is the source of all clouds and precipitation. Like carbon dioxide, water vapor absorbs heat given off by Earth. It also absorbs some solar energy.

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Mesosphere and Thermosphere

In the third layer, the mesosphere, temperatures again decrease with height until the mesopause. The mesopause is more than 80 kilometers above the surface and the temperatures approach -90°C. The fourth layer extends outward from the mesopause and has no well-defined upper limit. It is the thermosphere, a layer that contains only a tiny fraction of the atmosphere's mass. Temperatures increase in the thermosphere because oxygen and nitrogen absorb short-wave, high-energy solar radiation.

Movements of the atmosphere

Movements of the atmosphere allow a large quantity of solid and liquid particles to be suspended within it. Although visible dust sometimes clouds the sky, these relatively large particles are too heavy to stay in the air for very long. Still, many particles are microscopic and remain suspended for longer periods of time. These particles include sea salts from breaking waves, fine soil blown into the air, smoke and soot from fires, pollen and microorganisms lifted by the wind, and ash and dust from volcanic eruptions.

Earth-Sun Relationships

Nearly all of the energy that drives Earth's variable weather and climate comes from the sun. The earth absorbs only a tiny percentage of the energy given off by the sunless than one two-billionth. This may seem insignificant, but the amount is several hundred thousand times the electrical-generating capacity of the United States.

Primary and Secondary Pollutants

Primary pollutants are emitted directly from identifiable sources. Emissions from transportation vehicles account for nearly half the primary pollutants by weight. Secondary pollutants are not emitted directly into air. They form in the atmosphere when reactions take place among primary pollutants and other substances. For example, after the primary pollutant sulfur dioxide enters the atmosphere, it combines with oxygen to produce sulfur trioxide. Then the sulfur trioxide combines with water to create sulfuric acid, an irritating and corrosive substance.

Reactions and Sunlight

Reactions triggered by strong sunlight are called photochemical reactions. For instance, when nitrogen oxides absorb solar radiation, a chain of complex reactions begins. If certain volatile organic compounds are present, secondary products form that are reactive, irritating, and toxic. This noxious mixture of gases and particles is called photochemical smog.

The Seasons 2

Six months later, in December, when Earth has moved to the opposite side of its orbit, the Northern Hemisphere leans 23.5 degrees away from the sun. December 21 or 22 is the winter solstice or the first day of winter. On days between these extremes, Earth's axis is leaning at amounts less than 23.5 degrees to the rays of the sun.

Solar Energy

Solar energy is not distributed evenly over Earth's surface. The amount of energy received varies with latitude, time of day, and season. These variations in solar heating are caused by the motions of Earth relative to the sun and by variations in Earth's land and ocean surface. It is the unequal heating of Earth that creates winds and drives the ocean's currents. These movements transport heat from the tropics toward the poles, thus driving the phenomena we call weather.

Major Components

Sometimes the term air is used as if it were a specific gas, which it is not. Air is a mixture of different gases and particles, each with its own physical properties. The composition of air varies from time to time and from place to place. However, if the water vapor, dust, and other variable components were removed from the atmosphere, its makeup would be very stable worldwide up to an altitude of about 80 kilometers.

Troposphere

The atmosphere can be divided vertically into four layers based on temperature. The figure illustrates these layers. The bottom layer, where temperature decreases with an increase in altitude, is the troposphere. It is in this layer that essentially all-important weather phenomena occur. The thickness of the troposphere is not the same everywhere. It varies with latitude and the season. On average, the temperature drop continues to a height of about 12 kilometers, where the outer boundary of the troposphere, called the tropopause, is located.

Sun's Apparent Path

The changing orientation of Earth relative to the sun causes the sun's apparent path to vary with latitude and season. The angle of the noon sun can vary by up to 47 degrees (-23.5 degrees to +23.5 degrees) for many locations during the year. A mid-latitude city like New York, located about 40 degrees north latitude, has a maximum noon sun angle of 73.5 degrees when the sun's vertical rays reach their farthest northward location in June. Six months later, New York has a minimum noon sun angle of 26.5 degrees.

Composition of the Atmosphere

The composition of the atmosphere has changed dramatically over Earth's nearly 4.6 billion year history. It is likely that the Earth's earliest atmosphere was composed mainly of hydrogen and helium. These were the primary gases found within the dusty disk from which the planets formed. Hydrogen and helium are very light gases, and they eventually escaped Earth's gravity and floated off into space. The planet's next atmosphere is thought to have come from gases emitted during volcanic eruptions. At the time, the Earth's crust was still forming, so there was a great deal of volcanic activity. Volcanoes emit a mixture of ammonia, methane, carbon dioxide, and steam. Over time, the Earth began to cool and water vapor in the atmosphere condensed to form the hydrosphere.

The Seasons 3

The equinoxes occur midway between the solstices. September 22 or 23 is the date of the autumnal equinox and the start of autumn in the Northern Hemisphere. March 21 or 22 is the date of the spring equinox and the start of spring for the Northern Hemisphere. On these dates, the vertical rays of the sun strike the equator (0 degrees latitude) because Earth is in a position in its orbit such that the axis is tilted neither toward nor away from the sun.

Why is solar energy not distributed evenly over the Earth?

The movement of the Earth in relation to the sun, and the various topographical features found both on land and in the oceans, cause solar energy to be distributed unevenly across Earth.

Ozone 2

There is very little ozone in the atmosphere, and it is not distributed evenly. It is concentrated in a layer located between 10 and 50 kilometers above Earth's surface. In this altitude range, oxygen molecules (O2) are split into single atoms of oxygen (O) when they absorb ultraviolet (UV) radiation emitted by the sun. Ozone is then produced when a single atom of oxygen (O) and a molecule of oxygen (O2) collide. This collision must happen in the presence of a third, neutral molecule that acts as a catalyst. A catalyst allows a reaction to take place without being consumed in the process.

Pressure Changes

To understand the vertical extent of the atmosphere, examine the figure, which shows changes in atmospheric pressure with height. Atmospheric pressure is caused by the weight of the air above. At sea level, the average pressure is slightly more than 1,000 millibars (mb), or slightly more than 1 kilogram per square centimeter. One half of the atmosphere by mass lies below an altitude of 5.6 kilometers. Above 100 kilometers, only 0.00003 percent of all the gases making up the atmosphere exist.

Which statement best describes the climate of a specific place?

Typical summer weather is hot and dry, and winter weather is cold and snowy.

Earth's Orientation

We know that it is colder in the winter than in the summer. But why? Length of the day and a gradual change in the angle of the noon sun above the horizon affect the amount of energy Earth receives. Seasonal changes occur because Earth's position relative to the sun continually changes as it travels along its orbit. Earth's axis is not perpendicular to the plane of its orbit around the sun. Instead, it is tilted 23.5 degrees from the perpendicular. Because the axis remains pointed toward the North Star as Earth moves around the sun, the position of Earth's axis relative to the sun's rays is constantly changing. If the axis were not tilted, we would not have seasonal changes.

Height and Structure of the Atmosphere

Where does the atmosphere end and outer space begin? There is no sharp boundary. The atmosphere thins as you travel away from Earth until there are too few gas molecules to detect.

Today, Central City received 12 centimeters of rain, while Eastville received only 2 centimeters of rain. Which evidence could show that Central City has the rainier climate?

rainfall records over many years for the two cities

Which change to Earth would eliminate seasons and seasonal weather?

removing the tilt of Earth's axis

In which layers of Earth's atmosphere does temperature decrease with altitude?

troposphere and mesosphere