We live at the bottom of a vast ocean of air—the Earth's atmosphere. Like the water in the ocean, the air in the atmosphere is constantly pressing on the Earth's surface beneath it and on everything that it surrounds. The atmosphere exerts pressure because gravity pulls the gas molecules of the air toward the Earth. Gravity is an attraction among all […]

At irregular intervals of about three to eight years, a remarkable disturbance of ocean and atmosphere occurs in the equatorial Pacific region—El Nino. Its name comes from Peruvian fishermen, who refer to the Corriente del Nino or the “Current of the Christ Child,” to describe an invasion of warm surface water once every few years around Christmas time that greatly depletes their […]

Most people living in or near urban areas have experienced air pollution first hand. Perhaps you've felt your eyes sting or your throat tickle as you drive an urban freeway. Or you've noticed black dust on window sills or window screens and realized that you are breathing in that dust as well. AIR POLLUTANTS Air pollution is largely the result […]

A tornado is a small but intense vortex in which air spirals at tremendous speed. It is associated with thunderstorms spawned by fronts in the midlatitudes of North America. Tornadoes can also occur inside tropical cyclones (hurricanes). TORNADO CHARACTERISTICS A tornado, seen in Figure 4.32, appears as a dark funnel cloud hanging from the base of a dense cumulonimbus cloud. At […]

A thunderstorm is any storm that produces thunder and lightning. At the same time, thunderstorms can also produce high winds, hail, and tornadoes. They are typically associated with cumulus clouds that indicate the presence of rising, unstable air. It is this rising motion that produces the characteristic rainfall and lightning that accompany thunderstorms. Thunderstorms can range from fairly isolated, short-lived storms, sometimes called […]

Precipitation consists of liquid water drops and solid crystals that fall from the atmosphere and reach the ground. This precipitation can take several different forms. RAIN Rain is precipitation that reaches the ground as liquid water. Raindrops can form in warm clouds as liquid water, which through collisions can coalesce with other drops and grow large enough to fall to Earth. […]

FORMATION OF PRECIPITATION Clouds are the source of precipitation—the process that provides the fresh water essential for most forms of terrestrial life. Precipitation can form in two ways. In warm clouds, fine water droplets condense, collide, and coalesce into larger and larger droplets that can fall as rain. In colder clouds, ice crystals form and grow in a cloud that contains a mixture of […]

Some of the most familiar images of Earth acquired by satellite instruments are those of the Geostationary Operational Environmental Satellite (GOES) system. Images from the GOES series of satellites have been in constant use since 1974. The primary mission of the GOES series is to view cloud patterns and track weather systems by providing frequent images of the Earth from a consistent viewpoint in space provided by […]

Clouds are frequent features of the atmosphere. Views of the Earth from space show that clouds cover about half of the Earth at any given time. Low clouds reflect solar energy, thus cooling the Earth–atmosphere system, while high clouds absorb outgoing longwave radiation, thus warming the Earth– atmosphere system. One of the most familiar roles of clouds, however, is in producing precipitation. Clouds […]

What makes the water vapor in the air turn into liquid or solid particles that can fall to the Earth? The answer is that the air is naturally cooled. When air cools to the dew point, the air is saturated with water. Think about extracting water from a moist sponge. To release the water, you have to squeeze the sponge—that […]

Blistering summer heat waves can be deadly, with the elderly and the ill at most risk. However, even healthy young people need to be careful, especially in hot, humid weather. High humidity slows the evaporation of perspiration from our bodies, reducing its cooling effect. Clearly, it is not only the temperature of the air that controls how hot weather affects us—the amount of water vapor in […]

In this chapter, we focus on water in the air, both as vapor and as liquid and solid water. Precipitation is the fall of liquid or solid water from the atmosphere that reaches the Earth's land or ocean surface. It forms when moist air is cooled, causing water vapor to form liquid droplets or solid ice particles. If cooling is […]

Perhaps you've heard about acid rain killing fish and poisoning trees. Acid rain is part of the phenomenon of acid deposition. It's made up of raindrops that have been acidified by air pollutants. Fossil fuel burning releases sulfur dioxide (SO2) and nitric oxide (NO2) into the air. The SO2 and NO2 readily combine with oxygen and water in the presence of […]

The Earth is getting warmer. In February 2007, the Intergovernmental Panel on Climate Change (IPCC), a United Nations-sponsored group of more than 2000 scientists, issued a report saying that global warming is “unequivocal”. Is this recent warming an effect of human activity? In 1995 the IPCC concluded that human activity has probably caused climatic warming by increasing the concentration of greenhouse gases […]

We have learned some important principles about air temperatures in this chapter. Surface type (urban or rural), elevation, latitude, daily and annual insolation cycles, and location (maritime or continental) can all influence air temperatures. Now let's put all these together and see how they affect world air temperature patterns. First, we need a quick explanation of air temperature maps. Figure 3.21 shows a set of isotherms—lines connecting locations […]

Let's turn to how, and why, air temperatures vary around the world. Insolation from the Sun varies across the globe, depending on latitude and season. Net radiation at a given place is positive during the day, as the surface gains heat from the Sun's rays. At night, the flow of incoming shortwave radiation stops, but the Earth continues to radiate longwave […]

In general, the air is cooler at higher altitudes. Remember from Chapter 2 that most incoming solar radiation passes through the atmosphere and is absorbed by the Earth's surface. The atmosphere is then warmed at the surface by latent and sensible heat flows. So it makes sense that, in general, air farther from the Earth's surface will be cooler. We call […]

This chapter focuses on air temperature—that is, the temperature of the air as observed at 1.2 m (4 ft) above the ground surface. Air temperature conditions many aspects of human life, from the clothing we wear to the fuel costs we pay. Air temperature and air temperature cycles also act to select the plants and animals that make up the biological landscape of a region. […]

One of the most important factors affecting air temperatures over the long run is the greenhouse effect, in which atmospheric gases absorb outgoing longwave radiation and reradiate a portion back to the surface. This makes surface temperatures warmer. Apart from water vapor, carbon dioxide gas plays the largest role in the greenhouse effect and CO2 concentration is increasing. In the centuries before […]

The Earth's global radiation balance is the primary determinant of long-term surface temperature, which is of great importance to life on Earth. Because this balance can be affected by human activities, such as converting forests to pasturelands or releasing greenhouse gases into the atmosphere, it is important to monitor the Earth's radiation budget over time as accurately as possible. For nearly 20 years, NASA has studied the […]

Although the energy budgets of the Earth's surface and atmosphere are in balance overall, their budgets do not have to balance at each particular place on the Earth, nor do they have to balance at all times. At night, for example, there is no incoming radiation from the Sun, yet the Earth's surface and atmosphere still emit out going radiation. Net […]

Human activity around the globe has changed the planet's surface cover and added carbon dioxide to the atmosphere. Have we irrevocably shifted the balance of energy flows? Is our Earth absorbing more solar energy and becoming warmer? Or is it absorbing less and becoming cooler? If we want to understand human impact on the Earth–atmosphere system, then we need to examine the […]

The most familiar form of heat storage and transport is known as sensible heat—it's what you feel when you touch a warm object. When we use a thermometer, we are measuring sensible heat. Sensible heat transfer moves heat from warmer to colder objects by conduction when they are in direct contact. Sensible heat is also transferred by convection when a fluid such as the atmosphere […]

The Earth is surrounded by air—a mixture of various gases that reaches up to a height of many kilometers. This envelope of air makes up our atmosphere (Figure 2.13). It is held in place by the Earth's gravity. Almost all the atmosphere (97 percent) lies within 30 km (19 mi) of the Earth's surface. The upper limit of the atmosphere is […]

Most natural phenomena on the Earth's surface—from the downhill flow of a river to the movement of a sand dune to the growth of a forest—are powered by the Sun, either directly or indirectly. It is the power source for wind, waves, weather, rivers, and ocean currents, as we will see here and in later chapters. Although the flow of solar […]

All surfaces—from the fiery Sun in the sky to the skin covering our bodies—constantly emit radiation. Very hot objects, such as the Sun or a light bulb filament, give off radiation that is nearly all in the form of light. Most of this energy is visible light, which we perceive with the colors of the rainbow, but the Sun also […]

High above the Earth's surface lies an atmospheric layer rich in ozone—a form of oxygen in which three oxygen atoms are bonded together (O3). Ozone is a highly reactive gas that can be toxic to life and damaging to materials, but high in the atmosphere it serves an essential purpose—sheltering life on the Earth's surface from powerful ultraviolet radiation emitted by […]

So far, we have discussed the importance of the Earth's rotation on its axis. But what about the Earth's movement as it orbits the Sun? We refer to this motion as the Earth's revolution around the Sun. The Earth takes 365.242 days to travel around the Sun—almost a quarter of a day longer than the calendar year of 365 days. […]

There's an old Canadian joke that goes, “Repent! The world will end at midnight! or 12:30 A.M. in Newfoundland.” It's humorous because independent-minded Newfoundlers use a time zone that is a half-hour ahead of the other Canadian maritime provinces. It highlights the fact that one single instant across the world—no matter how cataclysmic—is simultaneously labeled by different times in different local places. […]

The problem of how to best display the Earth's surface has puzzled cartographers, or mapmakers, throughout history. The oldest maps were limited by a lack of knowledge of the world, rather than by difficulties caused by the Earth's curvature. They tended to represent political or religious views rather than geographic reality. Ancient Greek maps from the sixth century B.C. show the world […]

It is impossible to lay a flat sheet of paper over a sphere without creasing, folding, or cutting it—as you know if you have tried to gift-wrap a ball. This simple fact has caused mapmakers problems for centuries. Because the Earth's surface is curved, we cannot divide it into a rectangular grid anymore than we could smoothly wrap a globe in […]

The Earth spins slowly on its axis —an imaginary straight line through its center and poles—a motion we refer to as rotation. We define a solar day by one complete rotation, and for centuries we have chosen to divide the solar day into exactly 24 hours. The North and South Poles are defined as the two points on the Earth's […]

As we all learn early in school, the Earth's shape is very close to a sphere. Pictures taken from space by astronauts and by orbiting satellites also show us that the Earth is a ball rotating in space. Today it seems almost nonsensical that many of our ancestors thought the world was flat. But to ancient sailors voyaging across the […]

Within the last few years, remote sensing, geographic information systems, and GPS technology have been integrated into new and exciting Internet tools for visualizing the Earth. Google Earth and World Wind are outstanding examples of these Earth visualization tools. GOOGLE EARTH Google Earth is a program for personal computers that allows users to roam the Earth's surface at will and zoom […]

Another important geographic technique for acquiring spatial information is remote sensing. This term refers to gathering information from great distances and over broad areas, usually through instruments mounted on aircraft or orbiting spacecraft. These instruments, or remote sensors, measure electromagnetic radiation coming from the Earth's surface and atmosphere as received at the aircraft or spacecraft platform. The data acquired by remote sensors are […]

Maps, like books, are very useful devices for storing information, but they have limitations. Recent advances in computing capability have enabled geographers to develop a powerful new tool to work with spatial data—the geographic information system (GIS). A GIS is a computer-based system for acquiring, processing, storing, querying, creating, analyzing, and displaying spatial data. Geographic information systems have allowed geographers, geologists, geophysicists, ecologists, planners, […]

The latitude and longitude coordinates of a point on the Earth's surface describe its position exactly. But how are those coordinates determined? For the last few hundred years, we have known how to use the position of the stars in the sky coupled with an accurate clock to determine the latitude and longitude of any point. Linked with advances in mapping […]

Cartography is the field of geography concerned with making maps. A map is a paper representation of space showing point, line, or area data—that is, locations, connections, and regions. It typically displays a set of characteristics or features of the Earth's surface that are positioned on the map in much the same way that they occur on the surface. The map's […]

Geographers use a number of specialized tools to examine, explore, and interact with spatial data. One of the oldest tools is the map—a paper representation of space showing where things are. While maps will never go out of style, computers have enhanced our ability to store, retrieve, and analyze spatial data through the development of geographic information systems (GIS). Acquiring geographic information […]

Physical geography is concerned with the natural world around us—in short, with the human environment. Because natural processes are constantly active, the Earth's environments are constantly changing. Sometimes the changes are slow and subtle, as when crustal plates move over geologic time to create continents and ocean basins. At other times, the changes are rapid, as when hurricane winds flatten vast areas […]

As a part of your introduction to physical geography, it will be useful to take a look at the big picture and examine some ideas that arch over all of physical geography—that is, spheres, systems, and cycles. The first of these ideas is that of the four great physical realms, or spheres of Earth—atmosphere, lithosphere, hydrosphere, and biosphere. These realms […]

What is geography? Put simply, geography is the study of the evolving character and organization of the Earth’s surface. It is about how, why, and where human and natural activities occur and how these activities are interconnected. What makes geography different from other disciplines? Geography adopts a unique set of perspectives to analyze the world and its human and natural phenomena. These […]

PHYSICAL GEOGRAPHY IS AN integral part of a much larger area of understanding called geography. Most individuals define geography as a field of study that deals with maps. This definition is only partially correct. A better definition of geography may be the study of natural and human phenomena relative to a spatial dimension. The discipline […]