Weather And Climate

Britannica Illustrated Science Library

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© 2008 Editorial Sol 90

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International Standard Book Number (set):

978-1-59339-797-5 International Standard Book Number (volume):

978-1-59339-801-9 Britannica Illustrated Science Library: Weather and Climate 2008

Printed in China



Weather and Climate


PHOTOGRAPH ON PAGE 1 Tornado during an electrical storm, in Oklahoma, 1973





Climate Change

Page 74

A Sum of Factors


Between September 20 and September 25, 1998, Hurricane Georges lashed the Caribbean, leaving thousands of people homeless.

The flutter of a butterfly's wings in Brazil can unleash a tornado in Florida." That was the conclusion arrived at in 1972 by Edward Lorenz after dedicating himself to the study of meteorology and trying to find a way of predicting meteorological phenomena that might put the lives of people at risk. In effect, the atmosphere is a system so complicated that many scientists define it as chaotic. Any forecast can rapidly deteriorate because of the wind, the appearance of a warm front, or an unexpected storm. Thus, the difference continues to grow geometrically, and the reality of the next day is not the one that was expected but entirely

different: when there should have been sunshine, there is rain; people who planned to go to the beach find they have to shut themselves up in the basement until the hurricane passes. All this uncertainty causes many people who live in areas that are besieged by hurricanes or tropical storms to live in fear of what might happen, because they feel very vulnerable to changes in weather. It is also true that natural phenomena, such as tornadoes, hurricanes, and cyclones, do not in themselves cause catastrophes. For example, a hurricane becomes a disaster and causes considerable damage, deaths, and economic losses only because it strikes a populated area or travels over farmland. Yet in society, the idea persists that natural phenomena equate to death and destruction. In fact, experience shows that we have to learn to live with these phenomena and plan ahead for what might happen when they occur. In this book, along with spectacular images, you will find useful information about the factors that determine weather and climate, and you will be able to understand why long-term forecasts are so complicated. What changes are expected if global warming continues to increase? Could the polar ice caps melt and raise sea levels? Could agricultural regions slowly become deserts? All this and much more are found in the pages of the book. We intend to arouse your curiosity about weather and climate, forces that affect everyone. •



In this image of the Earth, one clearly sees the movement of water and air, which causes, among other things, temperature variations.

he constantly moving atmosphere, the oceans, the continents, and the great masses of ice are the principal components of the environment. All these constitute what is called the climatic system; they permanently interact with one another and transport water (as liquid or vapor), electromagnetic radiation, and heat.

Within this complex system, one of the fundamental variables is temperature, which experiences the most change and is the most noticeable. The wind is important because it carries heat and moisture into the atmosphere. Water, with all its processes (evaporation, condensation, convection), also plays a fundamental role in Earth's climatic system.

Global Equilibrium

The Sun's radiation delivers a large amount of energy, which propels the Earth's extraordinary mechanism called the climatic system. The components of this complex system are the atmosphere, hydrosphere, lithosphere, cryosphere, and biosphere. All these components are constantly interacting with one another via an interchange of materials and energy. Weather and climatic phenomena of the past—as well as of the present and the future—are the combined expression of Earth's climatic system. •


The atmosphere is always in motion. Heat displaces masses of air, and this leads to the general circulation of the atmosphere.



The hydrosphere is the name for all water in liquid form that is part of the climatic system. Most of the lithosphere is covered by liquid water, and some of the water even circulates through it.


Part of the energy received from the Sun is captured by the atmosphere. The other part is absorbed by the Earth or reflected in the form of heat. Greenhouse gases heat up the atmosphere by slowing the release of heat to space.


The surfaces of water bodies maintain the quantity of water vapor in the atmosphere within normal limits.


Living beings (such as plants) influence weather and climate. They form the foundations of ecosystems, which use minerals, water, and other chemical compounds. They contribute materials to other subsystems.

about 10%

Night and day, coastal breezes exchange energy between the hydrosphere and the lithosphere.



Water condensing in the atmosphere forms droplets, and gravitational action causes them to fall on different parts of the Earth's surface.



About 50 percent of the solar energy reaches the surface of the Earth, and some of this energy is transferred directly to different layers of the atmosphere. Much of the available solar radiation leaves the air and circulates within the other subsystems. Some of this energy escapes to outer space.

Essential for climatic activity. The subsystems absorb, exchange, and reflect energy that reaches the Earth's surface. For example, the biosphere incorporates solar energy via photosynthesis and intensifies the activity of the hydrosphere.


Represents regions of the Earth covered by ice. Permafrost exists where the temperature of the soil or rocks is below zero. These regions reflect almost all the light they receive and play a role in the circulation of the ocean, regulating its temperature and salinity.



Particles that escape into the atmosphere can retain their heat and act as condensation nuclei for precipitation.

The circulation of water is produced by gravity. Water from the hydrosphere infiltrates the lithosphère and circulates therein until it reaches the large water reservoirs of lakes, rivers, and oceans.





This is the uppermost solid layer of the Earth's surface. Its continual formation and destruction change the surface of the Earth and can have a large impact on weather and climate. For example, a mountain range can act as a geographic barrier to wind and moisture.




Volcanic eruptions bring nutrients to the climatic system where the ashes fertilize the soil. Eruptions also block the rays of the Sun and thus reduce the amount of solar radiation received by the Earth's surface. This causes cooling of the atmosphere.


Some gases in the atmosphere are very effective at retaining heat. The layer of air near the Earth's surface acts as a shield that establishes a range of temperatures on it, within which life can exist.



The percentage of solar radiation reflected by the climatic subsystems.


Pure Air

Pure Air he atmosphere is the mass of air that ■ envelops the surface of the Earth. Its composition allows it to regulate the quantity I and type of solar energy that reaches the surface of B the Earth. The atmosphere, in turn, absorbs energy B radiated by the crust of the Earth, the polar ice caps and the oceans, and other surfaces on the planet. Although nitrogen is its principal component, it also contains other gases, such as oxygen, carbon dioxide, ozone, and water vapor. These less abundant gases, along with microscopic particles in the air, have a great ^^m. influence on the Earth's weather and climate.

This layer, which begins at an altitude of about 310 miles (500 km), is the upper limit of the atmosphere. Here material in plasma form escapes from the Earth, because the magnetic forces acting on them are greater than those of gravity.


Carbon dioxide 0.04%

Other gases 0.03%

Oxygen 21%

Nitrogen 78%

Produced by the absorption of infrared emissions by the greenhouse gases in the atmosphere. This natural phenomenon helps to keep the Earth's surface temperature stable.


Polar meteorological satellites orbit in the exosphere.



Polar meteorological satellites orbit in the exosphere.


Found between an altitude of 55 and 300 miles (90500 km). The O2 and the N2 absorb ultraviolet rays and reach temperatures greater than 1,800° F (1,000° C). These temperatures keep the density of gases in this layer very low.


Created in the upper layers of the atmosphere when the solar wind generates electrically charged particles of solar radiation is reflected by the atmosphere.

Military satellites

Air friction shortens their useful life.

Rocket probes

Used for scientific studies of the higher regions of the atmosphere

of solar radiation is absorbed by the gases in the atmosphere.

Meteors become superheated by friction with the molecules of the gas in the atmosphere. Particles that skip across the atmosphere are called shooting stars.

Located between an altitude of 30 to 55 miles (50-90 km), it absorbs very little energy yet emits a large amount of it. This absorption deficit causes the temperatures to decrease from 60° F to -130° F (20° C to -90° C) in the upper boundary of the mesopause.

Cosmic rays

Come from the Sun and other radiation sources in outer space. When they collide with the molecules of gas in the atmosphere, they produce a rain of particles.


Extends from an altitude of 6 miles to 30 miles (10-50 km). The band from 12 to 19 miles (20-30 km) has a high concentration of ozone, which absorbs ultraviolet radiation. A thermal inversion is produced in this layer that is expressed as an abrupt temperature increase beginning at an altitude of 12 miles (20 km).

Noctilucent clouds

The only clouds that exist above the troposphere. They are the objects of intense study.


Starts at sea level and goes to an altitude of six miles (10 km). It provides conditions suitable for life to exist. It contains 75 percent of the gases in the atmosphere. Meteorological conditions, such as the formation of clouds and precipitation, depend on its dynamics. It is also the layer that contains pollution generated by human activities.

Rotation of the Earth


Intertropical Convergence Zone (ITCZ)


These winds blow toward the Equator.

High-pressure area

Low-pressure area o

Masses of cold air descend and prevent clouds from forming.

Warm air rises and forms an area of low pressure (cyclone).

The descending air forms an area of high pressure (anticyclone).

Atmospheric Dynamics

The atmosphere is a dynamic system. Temperature changes and the Earth's motion are responsible for horizontal and vertical air displacement. Here the air of the atmosphere circulates between the poles and the Equator in horizontal bands within different latitudes. Moreover, the characteristics of the Earth's surface alter the path of the moving air, causing zones of differing air densities. The relations that arise among these processes influence the climatic conditions of our planet. •

rising air leads to the formation of clouds.

Changes in Circulation

^^ Irregularities in the topography of the surface, abrupt changes in temperature, and the influence of ocean currents can alter the general circulation of the atmosphere. These circumstances can generate waves in the air currents that are, in general, linked to the cyclonic zones. It is in these zones that storms originate, and they are therefore studied with great interest. However, the anticyclone and the cyclone systems must be studied together because cyclones are fed by currents of air coming from anticyclones.

FERREL CELL A part of the air in the Hadley cells follows its course toward the poles to a latitude of 60° N and 60° S.

Intertropical Convergence Zone (ITCZ)


These winds blow toward the Equator.

Low-pressure area

High-pressure area

^^ Warm air rises and causes a low-pressure M^M area (cyclone) to form beneath it. As the air cools and descends, it forms a high-pressure area (anticyclone). Here the air moves from an anticyclonic toward a cyclonic area as wind. The warm air, as it is displaced and forced upward, leads to the formation of clouds.

Masses of cold air descend and prevent clouds from forming.

High and Low Pressure


The Coriolis effect is an apparent deflection of the path of an object that moves within a rotating coordinate system. The Coriolis effect appears to deflect the trajectory of the winds that move over the surface of the Earth, because the Earth moves beneath the winds. This apparent deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The effect is only noticeable on a large scale because of the rotational velocity of the Earth.

Rotation of the Earth


Warm air rises and forms an area of low pressure (cyclone).

The descending air forms an area of high pressure (anticyclone).


At the poles, cold air descends moves toward the Equator.

O— Polar jet stream


Polar easterlies


Velocity 55 to 250 miles per hour (90-400 km/h)


1,000 to 3,000 miles

(1,610-4,850 km)


lto3 miles

(1.6-4.8 km)

Discovered in the 19th century through the use of kites. Airplanes can shorten their flying time by hitching a ride on them. Their paths are observed to help predict the weather.

Subtropical jet stream

Jet stream



Warm air ascends in the equatorial region and moves toward the middle latitudes, in which the Sun's average angle of incidence is lower than in the tropics.



The continuous lines are isobars (in this case, in the Southern Hemisphere), imaginary lines that connect points of equal pressure. They show depressions— centers of low pressure relative to the surroundings— and an anticyclone, a center of high pressure.

High-altitude Convergence Divergence air flow \ (jet stream)

Surface air flow

Forces in the upper-air currents, along with surface conditions, may cause air currents to flow together or may split them apart.

The waves in the upper layers are translated into cyclones and anticyclones at ground level.

The velocity creates a difference in air concentration between different systems.

The jet stream generates air rotation, or vorticity.


High-altitude Convergence Divergence air flow \ (jet stream)

Anticyclone "


Jet stream


Minimum wind velocity Maximum wind velocity (convergence) (divergence)

Anticyclone "


Minimum wind velocity Maximum wind velocity (convergence) (divergence)


Jet stream


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