The modern atmosphere

Question 1

What is the principal substance of the atmostphere?

Answer 1

The principal substance of this atmosphere is air, the medium of life as well as a major industrial and chemical raw material. Air is a simple mixture of gases that is naturally odourless, colourless, tasteless, and formless, blended so thoroughly that it behaves as if it were a single gas

Question 2

Where do we consider the top of our atmosphere to be/

Answer 2

As a practical matter, we consider the top of our atmosphere to be around 480 km above Earth’s surface, the same altitude we used in Chapter 2 for measuring the solar constant and insolation received.

Question 3

What is the Exosphere?

Answer 3

An extremely rarefied outer atmospheric halo beyond the thermopause at an altitude of 480 km; probably composed of hydrogen and helium atoms, with some oxygen atoms and nitrogen molecules present near the thermopause. “Outer sphere.”

Question 4

What are the atmospheric criteria?

Answer 4

Scientists use three atmospheric criteria—composition, temperature, and function—to define layers for distinct analytical purposes.

Question 5

How dose air pressure work?

Answer 5

Air pressure changes throughout the atmospheric profile. Air molecules create air pressure through their motion, size, and number, exerting a force on all surfaces they come in contact with.

Question 6

How is the atmosphere divided by the criterion of chemical composition?

Answer 6

By the criterion of chemical composition, the atmosphere divides into two broad regions, the heterosphere (80 to 480 km altitude) and the homosphere (Earth’s surface to 80 km altitude)

Question 7

Which sphere is the outer atmosphere in terms of composition and what altitude dose it begin?

Answer 7

The heterosphere is the outer atmosphere in terms of composition. It begins at about 80 km altitude and extends outward to the exosphere and interplanetary space

Question 8

How much of the atmosphere’s mass can be found in the hetrosphere?

Answer 8

Less than 0.001% of the atmosphere’s mass is in this rarefied heterosphere.

Question 9

Where dose the International Space Station orbit?

Answer 9

The International Space Station (ISS) orbits in the middle to upper heterosphere

Question 10

How do gasses in the heterosphere occur?

Answer 10

Gases in the heterosphere occur in distinct layers sorted by gravity according to their atomic weight, with the lightest elements (hydrogen and helium) at the margins of outer space and the heavier elements (oxygen and nitrogen) dominant in the lower heterosphere.

Question 11

Main points about the homosphere.

Answer 11

homosphere, extending from an altitude of 80 km to Earth’s surface. Even though the atmosphere rapidly changes density in the homosphere—increasing pressure toward Earth’s surface—the blend of gases is nearly uniform throughout. The only exceptions are the concentration of ozone (O3) in the “ozone layer,” from 19 to 50 km above sea level, and the variations in water vapour, pollutants, and some trace chemicals in the lowest portion of the atmosphere

Question 12

The air in the homosphere is a vast reservoir of what gas?

Answer 12

The air of the homosphere is a vast reservoir of relatively inert nitrogen, originating principally from volcanic sources. A key element of life, nitrogen integrates into our bodies not from the air we breathe but through compounds in food.

Question 13

Discuss Oxygen in the Homosphere…

Answer 13

Oxygen, a by-product of photosynthesis, also is essential for life processes. The percentage of atmospheric oxygen varies slightly over space, with changes in photosynthetic rates of vegetation with latitude, season, and the lag time as atmospheric circulation slowly mixes the air. Although it makes up about one-fifth of the atmosphere, oxygen forms compounds that compose about half of Earth’s crust. Oxygen readily reacts with many elements to form these materials.

Question 14

Discuss Argon in the Homosphere

Answer 14

The gas argon, constituting less than 1% of the homosphere, is completely inert (an unreactive “noble” gas) and unusable in life processes. All the argon present in the modern atmosphere comes from slow accumulation over millions of years. Because industry has found uses for inert argon (in lightbulbs, welding, and some lasers), it is extracted or “mined” from the atmosphere, along with nitrogen and oxygen, for commercial, medical, and industrial uses.

Question 15

Discuss particulates in the homosphere

Answer 15

The homosphere also contains variable amounts of particulates, solids and liquid droplets that enter the air from natural and human sources. These particles, also known as aerosols, range in size from the relatively large liquid water droplets, salt, and pollen visible with the naked eye to relatively small, even microscopic, dust and soot

Question 16

Discuss CO2

Answer 16

Carbon dioxide (CO2) is a natural by-product of life processes, a variable gas that is increasing rapidly. Although its present percentage in the atmosphere is small, CO2 is important to global temperatures

Question 17

What has the study of past atmospheres trapped in samples of glacial ice revealed?

Answer 17

The study of past atmospheres trapped in samples of glacial ice reveals that the present levels of atmospheric CO2 are higher than at any time in the past 800 000 years. Over the past 200 years, and especially since the 1950s, the CO2 percentage has increased as a result of human activities, principally the burning of fossil fuels and deforestation.

Question 18

By the criterion of temperature, how can the atmosphere be divided?

Answer 18

By the criterion of temperature, the atmospheric profile can be divided into four distinct zones—thermosphere, mesosphere, stratosphere, and troposphere

Question 19

Where is the thermosphere?

Answer 19

The thermosphere (“heat sphere”) roughly corresponds to the heterosphere (from 80 km out to 480 km). The upper limit of the thermosphere is the thermopause (the suffix -pause means “to change”). During periods of a less active Sun, with fewer sunspots and eruptions from the solar surface, the thermopause may lower in altitude from the average 480 km to only 250 km. During periods of a more active Sun, the outer atmosphere swells to an altitude of 550 km, where it can create frictional drag on satellites in low orbit.

Question 20

What temperature dose it rise to in the thermosphere?

Answer 20

temperatures rise sharply in the thermosphere, to 1200°C and higher.

Question 21

Why is the thermosphere not “hot” in the way we might expect it?

Answer 21

Despite such high temperatures, however, the thermosphere is not “hot” in the way you might expect. Temperature and heat are different concepts. The intense solar radiation in this portion of the atmosphere excites individual molecules (principally nitrogen and oxygen) to high levels of vibration. This kinetic energy, the energy of motion, is the vibrational energy that we measure as temperature. (Temperature is a measure of the average kinetic energy of individual molecules in matter

Question 22

What is heat and how is it created?

Answer 22

In contrast, heat is created when kinetic energy is transferred between molecules, and thus between bodies or substances. (By definition, heat is the flow of kinetic energy from one body to another resulting from a temperature difference between them

Question 23

Why can we not feel the heat in the thermosphere?

Answer 23

The thermosphere is not “hot” in the way we are familiar with, because the density of molecules is so low there that little actual heat is produced. The thermosphere would actually feel cold to us because the number of molecules is not great enough to transfer heat to our skin. (Scientists measure temperature indirectly at those altitudes, using the low density, which is measured by the amount of drag on satellites.) Closer to Earth’s surface, the atmosphere is denser. The greater number of molecules transmits their kinetic energy as sensible heat, meaning that we can measure and feel it.

Question 24

What is the mesosphere and where is it located?

Answer 24

The mesosphere is the area from 50 to 80km above Earth and is within the homosphere. As Figure 3.3 shows, the mesosphere’s outer boundary, the mesopause, is the coldest portion of the atmosphere, averaging –90°C, although that temperature may vary considerably (by 25–30 C°). Note in Figure 3.2b the extremely low pressures (low density of molecules) in the mesosphere.

Question 25

What are noctilucent clouds?

Answer 25

The mesosphere sometimes receives cosmic or meteoric dust particles, which act as nuclei around which fine ice crystals form. At high latitudes, an observer at night may see these bands of ice crystals glow in rare and unusual noctilucent clouds, which are so high in altitude that they still catch sunlight after sunset.

Question 26

What is the stratosphere and where is it located?

Answer 26

The stratosphere extends from about 18 to 50 km above Earth’s surface. Temperatures increase with altitude throughout the stratosphere, from –57°C at 18 km to 0°C at 50 km, the stratosphere’s outer boundary, called the stratopause. The stratosphere is the location of the ozone layer.

Question 27

What have stratospheric changes measured over the past 25 years shown us?

Answer 27

Stratospheric changes measured over the past 25 years show that chlorofluorocarbons are increasing and ozone concentrations decreasing. Greenhouse gases are also on the increase; a noticeable cooling of the stratosphere is the response.

Question 28

What is the troposphere?

Answer 28

The troposphere is the final layer encountered by incoming solar radiation as it surges through the atmosphere to the surface. This atmospheric layer supports life and the biosphere, and is the region of principal weather activity.

Question 29

How much of the atmospheric mass is contained in the troposphere?

Answer 29

Approximately 90% of the total mass of the atmosphere and the bulk of all water vapour, clouds, and air pollution are within the troposphere.

Question 30

What is the average temperature of the tropopause?

Answer 30

An average temperature of –57°C defines the tropopause, the troposphere’s upper limit, but its exact altitude varies with the season, latitude, and surface temperatures and pressures

Question 31

Where dose the troposphere occur?

Answer 31

Near the equator, because of intense heating from the surface, the tropopause occurs at 18 km; in the middle latitudes, it occurs at an average of 12 km and at the North and South Poles, it averages only 8 km or less above Earth’s surface

Question 32

Why is the tropopause like a lid?

Answer 32

The marked warming with increasing altitude in the stratosphere above the tropopause causes the tropopause to act like a lid, generally preventing whatever is in the cooler (denser) air below from mixing into the warmer (less dense) stratosphere

Question 33

What is the Normal lapse rate/

Answer 33

The average rate of temperature decrease with increasing altitude in the lower atmosphere; an average value of 6.5 C° per km, or 1000 m.

Question 34

What is the Environmental lapse rate

Answer 34

The actual rate of temperature decrease with increasing altitude in the lower atmosphere at any particular time under local weather conditions; may deviate above or below the normal lapse rate of 6.5 C° per km, or 1000 m.

Question 35

How is the atmosphere divided within the criterion of function?

Answer 35

According to our final atmospheric criterion of function, the atmosphere has two specific zones, the ionosphere and the ozonosphere (ozone layer), which together remove most of the harmful wavelengths of incoming solar radiation and charged particles.

Question 36

What is the ionosphere?

Answer 36

The outer functional layer, the ionosphere, extends throughout the thermosphere and into the mesosphere below (Figure 3.1). The ionosphere absorbs cosmic rays, gamma rays, X-rays, and shorter wavelengths of ultraviolet radiation, changing atoms to positively charged ions and giving the ionosphere its name. The glowing auroral lights discussed in Chapter 2 occur principally within the ionosphere

Question 37

How do distinct regions within the ionosphere affect broadcast communications and GPS?

Answer 37

Distinct regions within the ionosphere, known as the D, E, F1, and F2 layers, are important for broadcast communications and GPS signals. These regions reflect certain radio wavelengths, including AM radio and other shortwave radio broadcasts, especially at night. Activity such as solar flares can trigger radio blackouts. This also affects airplanes that fly over the Arctic; over the North Pole, these aircraft lose contact with geosynchronous satellites and must rely on radio communications, which can be disrupted in a blackout. Before they reach ground, GPS satellite signals must first pass through the ionosphere, where gases bend and weaken radio waves. Solar and geomagnetic storms that disturb the ionosphere can cause GPS position errors as large as 100 m.

Question 38

What is the ozonosphere or "ozone layer"?

Answer 38

That portion of the stratosphere that contains an increased level of ozone is the ozonosphere, or ozone layer. Ozone is a highly reactive oxygen molecule made up of three oxygen atoms (O3) instead of the usual two atoms (O2) that make up oxygen gas. Ozone absorbs the shorter wavelengths of ultraviolet (UV) radiation (principally, all the UVC, 100–290 nm, and some of the UVB, 290–320 nm).* In the process, UV energy is converted to heat energy, safeguarding life on Earth by “filtering” some of the Sun’s harmful rays. However, UVA, at 320–400 nm, is not absorbed by ozone and makes up about 95% of all UV radiation that reaches Earth’s surface.

Question 39

Explain UVA and UVB

Answer 39

Although UVA, with its longer wavelengths, is less intense than UVB, it penetrates skin more deeply. Studies over the past 20 years have shown that UVA causes significant damage in the basal (lowest) part of the epidermis, the outer layer of skin, where most skin cancers occur. UVA levels are fairly constant throughout the year during daylight hours and can penetrate glass and clouds. In contrast, UVB intensity varies by latitude, season, and time of day. UVB damages the skin’s more superficial epidermal layers and is the chief cause of skin reddening and sunburn. It, too, can lead to skin cancer

Question 40

What is the effect of human activities on the ozone layer?

Answer 40

The total amount of ozone in the stratosphere is presumed to have been relatively stable over the past several hundred million years (allowing for daily and seasonal fluctuations). Today, however, human activities are causing ozone depletion at a greater rate than if natural processes were acting alone.

Question 41

Explain the UV index

Answer 41

Weather reports regularly include the UV Index, or UVI, in daily forecasts to alert the public to the need to use sun protection, especially for children (Table 3.2). The UV Index is a simple way of describing the daily danger of solar UV-radiation intensity, using a scale from 1 to 11+. A higher number indicates a greater risk of UV exposure; an index of 0 indicates no risk, such as at night. Higher risk means that UV damage to skin and eyes can occur over a shorter time period. UV radiation varies spatially according to the amount of ozone depletion overhead, the season, and the local weather conditions.