48
Lectures
30
minutes/lecture
1.
Geology's Impact on History
If you could view Earth's history at high speed, you'd see continents whiz about, ocean basins grow and shrink, and mountain ranges rise and erode away. This lecture sets the stage for investigating our dynamic planet.
1.
Geology's Impact on History
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25.
Anatomy of an Earthquake—Sumatra
The 2004 Sumatra earthquake produced a massive tsunami that killed more than 200,000 people around the Indian Ocean. We look at the complex tectonic forces behind this cataclysm.
25.
Anatomy of an Earthquake—Sumatra
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2.
Geologic History—Dating the Earth
Discovering Earth's exact age took centuries of detective work. Rock strata provide relative ages, but only with the discovery of radioactivity was it possible to determine the absolute geologic timescale.
2.
Geologic History—Dating the Earth
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26.
History of Plate Motions—Where and Why
Earth's tectonic plates have been moving for at least as long as scientists can see back into the geologic record. Over time the continental fragments collect into supercontinents and then break apart again.
26.
History of Plate Motions—Where and Why
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3.
Earth's Structure—Journey to Earth's Center
Analysis of seismic waves from earthquakes allows scientists to map the structure inside Earth. Using this technique, we take a modern-day journey to the center of the Earth in the style of Jules Verne.
3.
Earth's Structure—Journey to Earth's Center
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27.
Assembling North America
North America has a fascinating geologic history, having continuously grown in size through collisions with other continents. The process of growth has been very different on the East and West coasts.
27.
Assembling North America
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4.
Earth's Heat—Conduction and Convection
We reverse the direction of the previous lecture to see how heat flows from the center of Earth toward the surface, exploring the phenomena of heat radiation, conduction, and convection.
4.
Earth's Heat—Conduction and Convection
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28.
The Sun-Driven Hydrologic Cycle
As fast as plate tectonics creates mountains, erosion tears them down. The principal agents of erosion are water and ice, which are part of a continuous cycle of moving water called the hydrologic cycle.
28.
The Sun-Driven Hydrologic Cycle
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5.
The Basics of Plate Tectonics
The theory of plate tectonics accounts for the existence of continents, oceans, mountains, earthquakes, volcanoes, mineral resource distribution, climate changes, and many other aspects of our planet.
5.
The Basics of Plate Tectonics
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29.
Water on Earth—The Blue Planet
Earth is unique in the solar system for having liquid water at its surface. Water is the single most important substance on our planet, controlling much of geology and allowing for the evolution of life.
29.
Water on Earth—The Blue Planet
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6.
Making Matter—The Big Bang and Big Bangs
We investigate the big bang and the early evolution of the universe to learn the origin of atoms, stars, and planets. The supernovae of dying stars played a key role in forging heavy elements.
6.
Making Matter—The Big Bang and Big Bangs
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30.
Earth's Atmosphere—Air and Weather
Earth's gravity is strong enough to hold onto an atmosphere of nitrogen and oxygen, while lighter gases have long since been lost to space. We explore the structure of the atmosphere and its circulation.
30.
Earth's Atmosphere—Air and Weather
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7.
Creating Earth—Recipe for a Planet
The solar system formed 4.6 billion years ago when a cloud of gas, dust, and ice began to collapse and rotate, with Earth accreting in the inner region of the disk. An enormous collision with the proto-Earth produced the Moon.
7.
Creating Earth—Recipe for a Planet
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31.
Erosion—Weathering and Land Removal
A mountain on the Moon can last for billions of years, but the same mountain on Earth is worn down in only tens of millions of years. The reason is the rapid rate of erosion on Earth due to its atmosphere and hydrosphere.
31.
Erosion—Weathering and Land Removal
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8.
The Rock Cycle—Matter in Motion
Though rocks may seem eternal, they are part of a continuous cycle of changing forms called the rock cycle, which begins with igneous rocks and can involve sedimentary and metamorphic phases.
8.
The Rock Cycle—Matter in Motion
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32.
Jungles and Deserts—Feast or Famine
The circulation of air within the atmosphere occurs predominantly in the form of six large convecting cycles called Hadley, Ferrel, and Polar cells. These control the distribution of precipitation and therefore of ecosystems.
32.
Jungles and Deserts—Feast or Famine
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9.
Minerals—The Building Blocks of Rocks
Rocks are made of minerals, which in turn are composed of different elements. Silicon and oxygen are the two most abundant elements in Earth's mantle and crust, and most rocks contain them.
9.
Minerals—The Building Blocks of Rocks
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33.
Mass Wasting—Rocks Fall Downhill
Once rock is broken into sediment, gravity makes sure that it heads downhill. Such "mass wasting" can occur as quickly as a landslide or as slowly as the piecemeal creep caused by repeated freezing and thawing.
33.
Mass Wasting—Rocks Fall Downhill
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10.
Magma—The Building Mush of Rocks
Most magma is generated beneath mid-ocean ridges, where plates move apart and rock moves toward the surface to fill the gaps. Magma forms in these places due to a process called pressure release.
10.
Magma—The Building Mush of Rocks
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34.
Streams—Shaping the Land
Once sediment is eroded and moved downhill, streams do most of the work from there. Streams are like a giant network of highways, continuously carrying rock from the mountains to the sea.
34.
Streams—Shaping the Land
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11.
Crystallization—The Rock Cycle Starts
When magma cools below certain temperatures, solid mineral crystals begin to grow. With continued cooling the entire magma will eventually crystallize, and the result is an igneous rock.
11.
Crystallization—The Rock Cycle Starts
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35.
Groundwater—The Invisible Reservoir
There is 100 times more water in the ground than in streams and lakes combined. Groundwater rarely consists of underground rivers, but rather of water percolating slowly though tiny pore spaces within rocks.
35.
Groundwater—The Invisible Reservoir
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12.
Volcanoes—Lava and Ash
Volcanoes form where magma reaches the surface and erupts—at which point the magma becomes lava. The different kinds of volcanoes are related to the tectonic settings in which they occur.
12.
Volcanoes—Lava and Ash
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36.
Shorelines—Factories of Sedimentary Rocks
The pounding of ocean waves is so strong that it sets all the continents reverberating. Shorelines are energetic environments where wave energy erodes rock and transports the sediments that become sedimentary rocks.
36.
Shorelines—Factories of Sedimentary Rocks
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13.
Folding—Bending Blocks, Flowing Rocks
Most rock of the crust and mantle is solid. And yet, over long timescales, the crust and mantle are in motion, bending and flowing. This lecture shows how rocks deform in an elastic, plastic, or brittle manner.
13.
Folding—Bending Blocks, Flowing Rocks
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37.
Glaciers—The Power of Ice
Glaciers are slowly moving rivers of flowing ice. They are remarkably efficient agents of erosion, tearing away mountains faster than any other geologic process.
37.
Glaciers—The Power of Ice
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14.
Earthquakes—Examining Earth's Faults
More than 200,000 earthquakes are recorded each year. We examine the types of faults along which they occur and the aftermath, which in some cases can leave the Earth ringing like a gong for months.
14.
Earthquakes—Examining Earth's Faults
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38.
Planetary Wobbles and the Last Ice Age
There is a cyclical pattern in the alternation of cold glacial periods and warmer interglacials, primarily due to variations in Earth's orbital characteristics. These are called Milankovitch cycles.
38.
Planetary Wobbles and the Last Ice Age
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15.
Plate Tectonics—Why Continents Move
Continents move because they are the surface expression of mantle convection. Two main forces are directly responsible for plate motions: slab pull and ridge push.
15.
Plate Tectonics—Why Continents Move
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39.
Long-Term Climate Change
Long timescale variations in climate are controlled predominantly by plate tectonics. The global cooling that has occurred over the past 50 million years is largely due to the formation of the Himalayan Mountains.
39.
Long-Term Climate Change
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16.
The Ocean Seafloor—Unseen Lands
The seafloor shows a tremendous diversity of features that are related to plate tectonics and the process of mantle convection.
16.
The Ocean Seafloor—Unseen Lands
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40.
Short-Term Climate Change
This lecture looks at climate change on timescales of decades to thousands of years. Several factors affect climate at these shorter timescales, among them variations in sunlight, ocean current fluctuations, and volcanoes.
40.
Short-Term Climate Change
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17.
Rifts and Ridges—The Creation of Plates
Oceans undergo reincarnation: they repeatedly die and are reborn. The Atlantic Ocean is only 180 million years old and will eventually close up again. The Red Sea appears to be a new ocean in the making.
17.
Rifts and Ridges—The Creation of Plates
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41.
Climate Change and Human History
The course of human civilization, which began at the same time as the warm, stable climates of the current interglacial period, is strongly tied to small changes in global and regional climates.
41.
Climate Change and Human History
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18.
Transform Faults—Tears of a Crust
The San Andreas is a transform fault that separates the North American and Pacific plates. Transform faults are actually rare on land, but mid-ocean ridges are intersected by countless such features.
18.
Transform Faults—Tears of a Crust
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42.
Plate Tectonics and Natural Resources
Did you ever wonder why there is gold in California, coal in Indiana, and oil in Iraq? During the natural process of plate tectonics, valuable metals and ores become concentrated to levels much higher than they normally exist.
42.
Plate Tectonics and Natural Resources
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19.
Subduction Zones—Recycling Oceans
Subduction zones are the most geologically exciting places on Earth. Here the most destructive earthquakes and volcanoes occur, and forces are generated that may rip supercontinents apart.
19.
Subduction Zones—Recycling Oceans
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43.
Nonrenewable Energy Sources
Most of the energy that humans now consume is in the form of nonrenewable sources, notably oil, natural gas, and coal. Uranium for powering nuclear reactors is also a limited, nonrenewable source.
43.
Nonrenewable Energy Sources
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20.
Continents Collide and Mountains Are Made
When plate motions bring continents in contact with each other, the result is the formation of mountains. A notable example is the Himalayas, produced by the continental collision of India with China.
20.
Continents Collide and Mountains Are Made
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44.
Renewable Energy Sources
We will eventually get almost all of our energy from solar-driven sources. These include solar panels and passive solar heating. Wind power, hydroelectric power, and biomass are also ultimately derived from sunlight.
44.
Renewable Energy Sources
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21.
Intraplate Volcanoes—Finding the Hot Spots
For years intraplate volcanoes such as those that produced the Hawaiian Islands were lumped together under the catch-all name of "hot spots," but recent work is showing that Earth has many different ways of making a volcano.
21.
Intraplate Volcanoes—Finding the Hot Spots
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45.
Humans—Dominating Geologic Change
Life has been altering the planet over roughly the past 4 billion years. What is remarkable, however, is the rapidity with which humans have become Earth's most powerful agent of geologic change.
45.
Humans—Dominating Geologic Change
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22.
Destruction from Volcanoes and Earthquakes
The largest earthquakes and volcanic eruptions release as much energy as the simultaneous explosion of tens of thousands of nuclear weapons. We look at the human consequences of these events.
22.
Destruction from Volcanoes and Earthquakes
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46.
History of Life—Complexity and Diversity
Life on Earth began at least 3.85 billion years ago, almost as soon as the conditions of a stable ocean would allow it. The path of evolution since then has been a remarkable one, and an integral part of Earth's story.
46.
History of Life—Complexity and Diversity
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23.
Predicting Natural Disasters
Volcanoes can be easily monitored, and they reveal many clues to an impending eruption as the magma slowly forces its way toward the surface. Earthquakes, by contrast, are not yet predictable.
23.
Predicting Natural Disasters
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47.
The Solar System—Earth's Neighborhood
Although Earth is unique in our solar system for having complex life, it is not unique in geologic processes such as volcanism, earthquakes, mantle convection, erosion, and even stream and lake formation.
47.
The Solar System—Earth's Neighborhood
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24.
Anatomy of a Volcano—Mount St. Helens
We examine the eruption of Mount St. Helens on May 18, 1980, triggered when an earthquake caused a gigantic avalanche that released pent-up magma and gases, leveling trees for over 600 square kilometers.
24.
Anatomy of a Volcano—Mount St. Helens
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48.
The Lonely Planet—Fermi's Paradox
What are the chances that there are other civilizations in our galaxy? Given the delicate balance of conditions that have allowed life to flourish on Earth, that number may be astonishingly small.
48.
The Lonely Planet—Fermi's Paradox
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24
Lectures
30
minutes/lecture
1.
Nature Abhors Extremes
From thunderstorms to typhoons to driving winds, the world's weather is often tumultuous, destructive, and surprising. And yet, all these phenomena represent Nature's attempt to mitigate extreme conditions. In this introduction, begin to explore some of these extremes as you examine the great complexity of the world weather system.
1.
Nature Abhors Extremes
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13.
The Global Atmospheric Circulation
After mastering the four forces that affect wind, step back to view their patterns of flow across the Earth's hemispheres. Examine the two models of air circulation that help account for large-scale air-circulation patterns and variations in temperature from the poles to the equator.
13.
The Global Atmospheric Circulation
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2.
Temperature, Pressure, and Density
Why do cold and warm fronts exist? Can you dig a well so deep you cannot pump water from it? Find the answer to these and other questions as you explore three key concepts of weather—temperature, pressure, and density—and the equation that sums up their relationship: the ideal gas law.
2.
Temperature, Pressure, and Density
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14.
Fronts and Extratropical Cyclones
In this lecture, you encounter some of the most dramatic air-flow patterns found in nature, the swift, turning winds of the cyclone. Trace the lifecycle of the extratropical cyclone, which draws its power from the huge energy generated when different air masses meet.
14.
Fronts and Extratropical Cyclones
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3.
Atmosphere—Composition and Origin
What is air made of? Is it always true that hot air rises and cold air sinks? Learn more about the air that surrounds us and cushions us from the outer reaches of space, and examine the various layers that make up the earth's atmosphere.
3.
Atmosphere—Composition and Origin
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15.
Middle Troposphere—Troughs and Ridges
Shift your eyes to the sky and examine what happens in a higher level of the atmosphere called the middle troposphere. With this examination, you discover two new features in large weather systems—troughs and ridges that occur in areas of very low and very high pressure—and see how these features affect the weather.
15.
Middle Troposphere—Troughs and Ridges
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4.
Radiation and the Greenhouse Effect
Energy radiates all around us, streaming in from sunbeams and emanating from every object on Earth. Investigate the various kinds of radiation represented on the electromagnetic spectrum, and see how these forms of energy—assisted by the greenhouse effect—make life possible on our planet.
4.
Radiation and the Greenhouse Effect
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16.
Wind Shear—Horizontal and Vertical
Expand your understanding of how air moves by taking a three-dimensional view of atmospheric circulation. Discover what happens when winds change direction and what conditions cause these changes in wind shear.
16.
Wind Shear—Horizontal and Vertical
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5.
Sphericity, Conduction, and Convection
If all the Earth receives energy from the sun, why are there such wide temperature differences across the planet? Why do we have seasons? Answer these questions while learning about how heat moves through the atmosphere via two basic processes: conduction and convection.
5.
Sphericity, Conduction, and Convection
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17.
Mountain Influences on the Atmosphere
In this lecture, investigate how mountains can disturb the atmosphere into which they intrude from below. Also, learn how these disturbances can be felt far and wide.
17.
Mountain Influences on the Atmosphere
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6.
Sea Breezes and Santa Anas
Gain an understanding of how wind works as you explore the way temperature and pressure drive sea breezes during the day and land breezes at night. Then apply these findings to a dramatic wind condition, the famous Santa Ana winds of California.
6.
Sea Breezes and Santa Anas
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18.
Thunderstorms, Squall Lines, and Radar
That familiar crash of thunder and the torrential rains that often accompany it are common weather during the warm season. Learn how these noisy storms can form near cold fronts associated with extratropical cyclones and see how scientists use radar to study these storms.
18.
Thunderstorms, Squall Lines, and Radar
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7.
An Introduction to Atmospheric Moisture
Add a new element to your understanding of the atmosphere—water—and learn some basic facts about air's capacity to hold water vapor, including the impact of temperature on atmospheric moisture and the implications for weather.
7.
An Introduction to Atmospheric Moisture
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19.
Supercells, Tornadoes, and Dry Lines
Delve deeper into tumultuous weather as you learn about the formation of towering supercell storms. You also take a detailed look at how the conditions that produce these storms can lead to deadly tornadoes.
19.
Supercells, Tornadoes, and Dry Lines
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8.
Bringing Air to Saturation
Why does dew form on some mornings? Why does it take longer to cook food at higher elevations? Discover the answer to these questions as you learn about saturation: the point where air holds the highest amount of water vapor that it can contain.
8.
Bringing Air to Saturation
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20.
Ocean Influences on Weather and Climate
With their massive volume and constantly moving currents, oceans provide a vast reservoir of energy. Explore how the winds help generate movement in the ocean and, in turn, how the oceans affect weather all over the world, creating a huge feedback loop that helps create our climate.
20.
Ocean Influences on Weather and Climate
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9.
Clouds, Stability, and Buoyancy, Part 1
One of the most familiar and beautiful features of weather is the cloud. In this lecture, examine different kinds of clouds, learn how clouds are born, why and how they take their distinctive shapes, and what kinds of conditions are likely to produce clouds.
9.
Clouds, Stability, and Buoyancy, Part 1
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21.
Tropical Cyclones
Building on your understanding of how the ocean affects weather, turn your attention to the tropical cyclone, generally known as the hurricane or typhoon. Examine the typical structures of the tropical cyclone, and investigate the conditions needed to unleash these dangerous storms.
21.
Tropical Cyclones
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10.
Clouds, Stability, and Buoyancy, Part 2
Continue your discussion of clouds as you take a closer look at the climates and precipitation relating to this weather phenomenon. Discover why some clouds produce rain while others do not and see why deserts are often found on the lee side of mountains.
10.
Clouds, Stability, and Buoyancy, Part 2
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22.
Light and Lightning
Here, you bring together all you've learned in earlier lectures about the composition of air, the electromagnetic spectrum, the condensation of liquid, and the role of oceans in our climate, and use that information to explore two dazzling phenomena: light and lightning.
22.
Light and Lightning
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11.
Whence and Whither the Wind, Part 1
Move from clouds to wind as you begin to explore how and why air is transported around the globe. Examine how conditions, including differences in air pressure and temperature as well as the rotation of the Earth, determine where winds arise and the direction in which they blow.
11.
Whence and Whither the Wind, Part 1
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23.
Prediction and Predictability
Scientists have learned a lot about how weather works and have developed sophisticated tools to predict what may happen in our weather. You learn about the sophisticated numerical models these experts use, as well as the inevitable limitations of those models.
23.
Prediction and Predictability
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12.
Whence and Whither the Wind, Part 2
In addition to pressure differences and the Earth's rotational movement, two other forces help to determine the winds' strength and direction: friction and centripetal force. Learn about these two forces and examine how they shape the winds the world over.
12.
Whence and Whither the Wind, Part 2
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24.
The Imperfect Forecast
Despite all their knowledge and tools, scientists cannot make perfect predictions. Find out why, using the example of Hurricane Rita in 2005, and explore the deep complexity of weather and climate that makes the subject of meteorology one that continues to fascinate.
24.
The Imperfect Forecast
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