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CHAPTER 7: Introduction to the Atmosphere


Summary of the Chapter

This chapter introduces the student to the study of climatology and meteorology. The chapter begins with an examination of the composition and structure of the atmosphere. According to temperature change with altitude, seven different layers can be identified in the atmosphere. The lowest layer, the troposphere, extends from the surface to a height of 11 kilometers. This layer contains the majority of the atmosphere's mass and is the location for most of the Earth's weather. Characteristics of the other six layers are described in detail.

The gases nitrogen and oxygen together make up about 99% of the volume of the dry atmosphere. The remaining 1% is comprised of a number different gases of which ozone, carbon dioxide, nitrous oxide, and methane are the most important to life on the Earth. Ozone is concentrated in a layer that extends from 15 to 55 kilometers above the Earth's surface. Ozone is important to life because it absorbs harmful ultraviolet radiation from the Sun. Recent investigations of the ozone layer have discovered areas of severe thinning located primarily at the South Pole. Researchers have determined that this thinning is caused by the emission of the artificially produced chemical chlorofluorocarbon into our atmosphere.

Several gases found in the atmosphere have the ability to absorb infrared radiation from the Earth's surface and atmosphere giving rise to the greenhouse effect. The greenhouse effect aids in the heating of the Earth's atmosphere and surface. Without it, the average temperature of the planet would be 33 degrees Celsius colder. Three important gases involved in the greenhouse effect process are methane, carbon dioxide, and nitrous oxide. The concentration of these gases in our atmosphere has been increasing since the beginning of the Industrial Revolution primarily because of the burning of fossil fuels. Other gases involved in the greenhouse effect include: ozone, water vapor, and chlorofluorocarbons.

A number of factors can influence the intensity of the solar radiation received at the Earth's surface. In the previous chapter (6. Matter and Energy), we discovered that the Sun can vary in its output of radiation and that a variety of geometrical relationships between the Earth and the Sun have considerable effect on the intensity and duration of incoming solar radiation. As the solar radiation passes through the Earth's atmosphere the processes of scattering, absorption, and reflection can also reduce the intensity of the shortwave beam.

The shortwave energy received by the Earth is balanced by a similar quantity of longwave radiation leaving back to space. This process is called the planetary energy balance. In this chapter, models of global shortwave and longwave dynamics were developed. Latitudinally, amounts of incoming shortwave and outgoing longwave radiation are not balanced. From 30 degrees North to 30 degrees South incoming shortwave radiation exceeds outgoing terrestrial radiation creating a surplus of energy at these latitudes. At latitudes 30 to 90 degrees North and South the reverse holds true and these regions have a deficit of energy. Several systems, like oceanic and atmospheric circulation, act to redistribute the surplus of energy at the tropics to the middle and high latitudes.

Radiation energy absorbed at the Earth's surface or within its atmosphere is normally converted into a number of different forms of energy and used in a variety of natural processes. One important conversion involves the creation of heat energy that is used to warm the Earth's surface and atmosphere. The generation of heat energy is strongly correlated to the quantity of shortwave radiation received. As discussed earlier, the amount of insolation being received by a location on the Earth varies both spatially and temporally because of Sun-Earth geometry, Earth rotation, and spatial differences in the Earth's atmospheric transparency.

Temperature can be defined as the intensity or degree of hotness of a body. A number of measurement scales have been invented to measure temperature. Heat is a measure of the quantity of heat energy present in a body. The heat contained in a body depends not only on its temperature but also its mass. Daily and annual fluctuations in temperature at the Earth's various locations is caused by variations in the input and output of net radiation. Spatial and temporal patterns of temperature are also influenced by factors like altitude, ocean currents, and surface properties.

Wind can be simply defined as air in motion. Air moves above the Earth's surface because of spatial differences in the density of the atmosphere. Newton's laws of motion suggest that wind should blow from areas of high density to areas of low density. We can measure the density of the air through atmospheric pressure. The speed of wind is controlled by pressure gradient force. Pressure gradient force can be simply described as the rate of pressure change (pressure gradient) over space.

Once in motion air is influenced by a number of forces. The rotation of the Earth causes medium and large scale movements of air to be deflected from their intended path. The magnitude of this force, known as Coriolis force, is controlled by the latitude of the location and the speed of the wind. Another force that acts on wind is centripetal force. This force is active when wind is flowing around curved paths, and high or low pressure centers. The final force that can influence moving air is friction. However, friction only acts on wind that is flowing near the surface of the Earth.

A variety of different types of large scale winds have been described by scientists. A geostrophic wind occurs in regions of the atmosphere (1 kilometer above the Earth's surface) where friction is low and the air tends to flow in a straight path. In geostrophic winds, only two forces are active: pressure gradient force and Coriolis force. Winds blowing in the upper atmosphere in curved paths are called gradient winds. These winds are influenced by the same forces as geostrophic winds plus the effect of centripetal force. Winds near the Earth's surface are called friction layer winds. Friction layer winds are the result of pressure gradient force, Coriolis force, centripetal force, and frictional force.

There are a number of unique types of circulation that exist at local and regional scales. These winds are primary the result of thermally generated circulation systems. In these systems, warm temperatures create areas of low atmospheric pressure on the Earth's surface, while areas of high pressure are generated when temperatures are relatively cold. Once established, the thermal gradient then develops a flow of air that goes from high to low pressure on the Earth's surface. Winds of this sort include, land and sea breeze, mountain and valley breeze, and on a regional scale monsoon winds.

At the global scale, consistent patterns of air flow can be seen at the Earth's surface and within its upper atmosphere. Global winds develop because of latitudinal variations in atmospheric pressure. However, these differences in pressure are not just the result of the differential heating of the Earth's surface. At approximately 30 degrees North and South latitude, the subtropical high pressure zone forms because of the presence of descending air from the upper atmosphere. The sub-polar lows, located at about 60 degrees North and South latitude, develop because of the dynamic interaction of cold polar air with warm moist subtropical air masses. This interaction causes frontal lifting and the development of cyclonic storms. Surface winds move from areas of high pressure to low pressure. The course of this movement is also altered by the influence of Coriolis force causing the development of the trade winds (0 to 30 degrees N and S), the westerlies (30 to 60 degrees N and S) and the polar easterlies (60 to 90 degrees N and S). Upper atmosphere winds are generally poleward and westerly direction. Their development is related to the presence of the Hadley, Ferrel and Polar circulation cells in the North and South hemisphere. Associated with the upper air winds are narrow regions of intensification where fast moving air is channeled into west to east flowing jet streams. Jet streams can be found over the subtropical high zones and the sub-polar lows.

An air mass is a large region of surface air of similar temperature and humidity characteristics. These masses of air move across the planet (as a part of global circulation) influencing the regional climate of regions of the globe for days to weeks. Climatologists have classified air masses based on their air temperature and moisture characteristics. The meeting of two air masses frequently produce a front. At these frontal zones differences in temperature can cause one mass to be displaced over another. The four main types of fronts are: stationary, cold, warm and occluded.

Mid-latitude cyclones are storms that develop when cold polar air interacts with subtropical air in the mid-latitudes. The result of this interaction is the development of a large (2000 km in diameter) rotating vortex of air with low atmospheric pressure. Also, common with these storms is the development of cold and warm fronts that are positioned to form a wave. Precipitation is found at the center of the storm and along the fronts where warm air is lifted over cooler air.

Thunderstorms are small (1 to 10 kilometers in diameter) storms that develop mainly in the tropics and in the mid-latitudes. Thunderstorms form when moist, unstable air is lifted vertically in to the atmosphere. The lifting process causes the moist air to cool causing condensation, cumulus cloud development and the release of latent heat. If enough moisture is available, the release of latent heat can enhance the vertical development of these storms to the top of the troposphere producing a cumulonimbus cloud. Development of the storm ends normally in a few hours when most of the water vapor is converted into precipitation. At this point, gravity and internal circulation then directs the precipitation to the ground surface producing heavy rain. Some mid-latitude thunderstorms can be converted into severe storms through additional uplift due to the presence of a mid-latitude cyclone. Severe thunderstorms can have hail, strong winds, thunder, lightning, intense rain, and tornadoes.

Weather in the tropics is characterized by convective storms that develop with the intertropical convergence zone, the hot clear weather associated with the subtropical high pressure zone, and severe oceanic cyclonic storms known as hurricanes. The animation in section 7u illustrates the seasonal movements of the intertropical convergence zone and subtropical high pressure zone. Note that areas near the equator tend to be under the influence of the intertropical convergence longer than areas further away. This phenomenon also causes regions away from the equator to experience distinct wet and dry seasons. Hurricanes are intense cyclonic storms that only develop over the tropical oceans. Atmospheric pressure at the center of these storms averages about 950 millibars. This extremely low pressure creates intense damaging winds. Hurricanes are composed of numerous bands of thunderstorms, which are produced by the release of latent heat from the condensation process. The lifespan of these storms is usually about 7 days. Most storms die when they are cutoff from their supply of latent heat energy. This occurs with landfall or when the storm moves to cooler ocean surfaces.

The Koppen climate classification system is the most widely used system for classifying the Earth's climatic types. This system recognizes five major types of climate. From the equator to the poles we have: A - Tropical Moist Climates; B - Dry Climates; C - Mid-Latitude Climates with Mild Winters; D - Mid-Latitude Climates with Cold Winters; and E - Polar Climates. Each one of these climates has sub-classifications that generally differ in the timing and quantity of their precipitation.

A number of factors influence the climate of a location. These factors include: a) Latitude and its influence on solar radiation received; b) Air mass influences; c) Location of high and low pressure systems; d) Heat exchange from ocean currents; e) Location of mountain barriers; f) Pattern of prevailing winds (including monsoons); g) Distribution of land and sea; and h) Altitude. The first three of these factors is examined in relationship with the Koppen climate classification system and the climatic data for some selected locations on the Earth.

Urban climates differ from rural climates. In general, urban climates tend to be warmer, have more precipitation and different wind patterns. The urban environment modifies its climate in a number of ways: 1) the surface materials in cities absorb more shortwave radiation; 2) configuration of building increases the absorption of shortwave radiation at low Sun angles and reduces the loss of longwave radiation at night; 3) transportation, industry and the heat of buildings artificially warm the air surrounding cities; 4) precipitation is higher in cities because increased thermal uplift and because of a greater quantity of condensation nuclei (dust); and 5) winds are for the most part reduced by the increased friction of the city surface. However, some street/building configurations can increase with speeds through tunneling.

Scientists are busy reconstructing past climatic conditions because of the belief that the past is the key to our future. There are three main categories of data used in this reconstruction: 1) meteorological records; 2) written documents and descriptive accounts; and 3) physical and biological proxy data. Meteorological records provide measurements of specific climatic variables on a variety of temporal and spatial scales. A standardized global network of weather stations started developing at the turn of this century. This network, however, has some problems due to short records of observation and a lack of stations over the world's oceans and in less developed countries. Recent advances in instrumentation have allowed us to gather climatic data globally from satellites. Written documents and descriptive accounts of weather are normally very subjected. However, some accounts describe features of climatic change that are based on biological or physical phenomena. These accounts are much more creditable. For example, blossom dates of trees, dates of water body freezing, and effects on crops. Scientists have used a variety of biological and physical proxy data to reconstruct temperatures far into the Earth's past. The accuracy of these reconstructions is dependent on how closely the climatic variable influences the phenomenon of study. Error can creep into these analyses if some other variable (besides the climatic variable) is also influencing the proxy phenomenon.

The Earth's climate is variable. Over the last billion years, global average temperature has fluctuated by as much as 15 degrees Celsius from the value observed today. For much of this history, average global temperatures have been warmer. There have, however, been periods when temperatures were much colder and glaciers covered vast regions on the Earth's surface. For example, for much of the past 2 million years global temperatures have been 2 to 5 degrees cooler than they are today. This climate caused the formation of vast continental ice sheets over most of North America and in selected regions in Europe and Asia. The past 14,000 years have been a time of glacial retreat because of generally warmer global temperatures.

A variety of mechanisms can cause climate change. Four of the most important mechanisms are examined in detail. The first mechanism involves variations in the Earth's orbital characteristics. The orbital characteristics that are involved include changes in the Earth's tilt, variations in the timing of aphelion and perihelion, and changes to the shape of the Earth's orbital path around the Sun. As the Earth travels through space, these three separate cyclic variations combine to produce long-term variations in the amount of solar radiation received by the Earth's surface. The amount of carbon dioxide in the Earth's atmosphere influences the strength of the atmosphere's greenhouse effect. Natural variations in the concentration of carbon dioxide occur because of changes in global mean temperature. When global temperatures are warm there is a net movement of carbon dioxide from the oceans into the atmosphere. Colder mean temperatures reverse this process, lowering the concentration of carbon dioxide in the atmosphere. Since the Industrial Revolution, humans have been artificially increasing the concentration of carbon dioxide in the atmosphere through the burning or fossil fuels and the alteration of ecosystems. Volcanic eruptions can cause short-term cooling of the Earth's climate. This cooling occurs because some volcanic eruptions release material into the stratosphere that effectively blocks the reception of solar radiation by the Earth's surface. Eruptions that can cause climatic change must be rich in sulfur dioxide. The final mechanism that can cause climate change is variations in the Sun's output of radiation. Satellite measurements indicate that the Sun's output can vary by as much as 0.1% over a 18 month period. A variation of 1% would cause average global temperature to change by 1 degree Celsius.

El Niño is the name given to the infrequent development of warm ocean surface waters along the coast of Ecuador and Peru. It develops when there is change in the circulation of the atmosphere across the tropical pacific. Globally, the development of El Niño is also associated with a number of other climatic changes in other parts of the world.


List of Key Terms

Adiabatic, Absorption, Advection, Air Mass, Albedo, Altocumulus Clouds, Altostratus Clouds, Ammonia, Angle of Incidence, Anticyclone, Aphelion, Atmospheric Pressure, Autumnal Equinox,


Carbon Dioxide, Centripetal Acceleration, Centripetal Force, CFC, Chlorofluorocarbons, Cirrus Clouds, Cirrostratus Clouds, CLIMAP Project, Climatic Optimum, Cold Front, Condensation, Condensation Nuclei, Conduction, Convection, Convergence, Coriolis Force, Counter-Radiation, Cumulus, Cumulonimbus, Cumulus Clouds, Cyclogenesis, Cyclone, Cyclonic,

Day Length, Denitrification, Density, Deposition, Dew Point, Diffused Solar Radiation, Diffused Insolation, Diffusion, Disturbance, Direct Insolation, Direct Solar Radiation, Divergence, Dry Line,

Easterly Wave, Eccentricity, El Niño, Energy, Environmental Lapse Rate, Equinox, Evaporation, Eye,

Ferrel Cell, Force, Force of Acceleration, Friction, Frictional Force, Frictional Deceleration, Front, Frontal Cyclone, Frontal Uplift, Frontal Zone,

Geostrophic Wind, Glacial, Gradient Wind, Gravity, Greenhouse Effect, Greenhouse Gas, Gust Front,

Hadley Cell, Hail, Heat, Heat Energy, High Pressure, Holocene Epoch, Horizon, Hurricane,

Ice Age, Ideal Gas Law, Industrial Revolution, Infrared Radiation, Interglacial, Intertropical Convergence Zone, Insolation, Isobar, Isoline, Isotherm, Isothermal,

Land Breeze, Langley, La Niña, Latent Heat, Latent Heat Flux, Lightning, Little Climatic Optimum, Little Ice Age, Longwave Radiation, Low Pressure,

Mass, Meridional, Meridional Transport, Mesopause, Mesosphere, Methane, Mid-Latitude Cyclone, Milankovitch Theory, Millibar, Monsoon, Montreal Protocol, Mountain Breeze,

Net Radiation, Newton, Nimbostratus Clouds, Nitrogen Fixing, Nitrous Oxide, Northeast Trades,

Obliquity, Occluded Front, Ocean Current, Orographic Lifting, Orographic Uplift, Ozone, Ozone Hole, Ozone Layer,

Perihelion, Photochemical Smog, Photosynthesis, Pleistocene, Polar Axis, Polar Cell, Polar Front, Polar High, Polar Jet Stream, Polar Stratospheric Cloud, Polar Vortex, Potential Evapotranspiration, Precession of the Equinox, Precipitation, Pressure, Pressure Gradient, Pressure Gradient Force, Proxy Data,

Radiometer, Rain, Reflection, Relative Humidity, Respiration, Roll Cloud,

Scattering, Sea Breeze, Sensible Heat, Sensible Heat Flux, Shortwave Radiation, Solar Insolation, Solar Radiation, Solstice, Source Region, Southeast Trades, Southern Oscillation, Specific Heat, Stationary Front, Stratocumulus Clouds, Stratosphere, Stratus Clouds, Subpolar Lows, Subtropical High Pressure Zone, Subtropical Jet Stream, Sulfur Dioxide, Sun, Sunspots,Specific Heat, Standard Sea-Level Pressure,Solar Noon, Solstice, Stratopause, Stratosphere, Summer Solstice, Sun, Surface Heat Flux,

Temperature, Terminal Velocity, Thermal Circulation, Thermal High, Thermal Low, Thermal Wind System, Thermosphere, Thunder, Thunderstorm, Tornado, Total Column Ozone, Trade Winds, Transpiration, Troposphere, Tropopause, Trough,

Ultraviolet Radiation, Urban Heat Island,

Valley Breeze, Venturi, Vernal Equinox, Volcanic, Volume,

Warm Front, Waterspout, Watt, Wein's Law, Westerlies, Wind,

Y-axis, Younger-Dryas,



Study Questions, Problems, and Exercises

Essay Questions

(1). Describe and compare the daily cycles of insolation, net radiation and temperature for Kelowna (50 degrees North latitude) on an average June 21st and December 22nd. In your essay, be sure to include information on the height of the Sun at solar noon (A=90-L±23.5), length of daylight for each of these days (approximately 8 vs 16 hrs), and the timing of minimum and maximum daily temperatures.

(2). How does the tilt of the Earth's axis influence the annual solar insolation received at a site located at 50 degrees South latitude?

(3). Why is ozone important for life on Earth? Where is it found and how is it formed? How is human activity influencing this important atmospheric gas?

(4). How is the incoming shortwave solar radiation from the Sun modified by the atmosphere and the Earth's surface?

(5). Describe the difference between the following two terms: heat and temperature.

(6). Describe the shortwave radiation cascade as it relates to the Earth's energy balance (see the following Link)?

(7). Discuss how the Greenhouse Effect works? How has human activity over the last few centuries enhanced this natural process? How will global warming change the environment of the Earth?

(8). Discuss the following energy balance equation in terms of two locations: the beautiful island of Hawaii and the highland plateau of Mongolia in the winter.

Q* = Kdown - Kup + Ldown - Lup


Q* is net radiation.

Kdown is income direct and diffuse solar radiation or insolation.

Kup is shortwave radiation reflected from the Earth's surface back to space.

Ldown is counter-radiation because of the greenhouse effect.

Lup is the emission of longwave radiation from the Earth's surface back to space.


(9). Name and describe the characteristics of the various layers found in the atmosphere.

(10). What is a hurricane? Where, when and why does it form? How is global warming going to influence hurricane intensity and frequency.

(11). In a diagram, indicate the fronts, wind directions, pressure pattern, and precipitation pattern associated with a mature mid-latitude cyclone.

(12). The following diagram describes the major pressure systems on the surface of the Earth. On this diagram sketch in the surface wind directions associated with these pressure systems on an Earth which is spinning clockwise from the northpole.


(13). Discuss the formation and characteristics of the various types of thunderstorms.

(14). Describe the climatic characteristics of the following Koppen Climate Classifications: Cfa, Cs, and Cfb.

(15). What factors are responsible for the altered micro-climate of urban areas?

(16). Why does the jet stream in the Northern Hemisphere move north in the summer and south in the winter ?

(17). Four mechanisms of climatic change were discussed in class. What were they, how do they function and what type of time scale do they operate in.

(18). When did the Little Ice Age occur and how much colder was the global temperature at this time?

(19). How can we reconstruct past ocean temperature from the plankton species known as Foraminifera?

(20). Outline the climatic characteristics and associated weather phenomena of the following three Koppen climate regimes Am, Af, and Aw.

(21). Why do urban areas have more energy available for the creation of sensible heat than rural areas?








Created by Dr. Michael Pidwirny & Scott Jones University of British Columbia Okanagan

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Copyright © 1999-2009 Michael Pidwirny

05/25/2009 9:50