BYU Geography: Lesson 4

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prevailing winds
Some areas have winds that blow from the same direction most of the time. These are called prevailing winds. In the northern US, the prevailing winds are called westerlies because the wind flows generally from the west towards the east. The prevailing winds significantly impacted early shipping routes because the ships relied on wind power to move across the oceans.
Look at Figure 4.1.1 and think about what you have learned about air pressure at various latitudes. Do subtropical areas generally have high pressure, or do they have low pressure?[/HTML]
high pressure
What is the name for horizontally flowing air?
wind
Do low pressure areas typically have warmer air or colder air than high pressure areas?
Low pressure areas are generally warmer than high pressure areas.
Which direction do the southeast trade winds blow?
northwest
How do low pressure systems and high pressure systems interact to move air?
The variations in temperature cause air to develop currents and cycle around the earth.
What is the name for winds that regularly blow the same direction?
prevailing winds
Does the North Pole have a high pressure system or a low pressure system?
high pressure system
What two factors influence air pressure?
altitude and heat influence air pressure
What wind systems do aircraft frequently take advantage of to fly more quickly?
jet streams
If you were sailing a ship from Europe across the Atlantic Ocean to the US, what wind system would most likely fill the sails and take you where you wanted to go?
the southeast trade winds
What is a jet stream?
The jet streams are fast-moving prevailing winds that are very high up in the atmosphere.
ocean currents
Like the atmosphere, the oceans have currents that have an impact on temperature. The currents are like rivers running through the oceans. They usually flow in a curricular pattern. In the Northern Hemisphere, the currents rotate clockwise, and in the Southern Hemisphere they rotate counterclockwise. The movement of the currents helps moderate ocean temperatures. The water moves between the polar and equilateral regions, warming as it moves through the tropics and cooling in the polar regions. Warm ocean currents make nearby coastal regions warmer and cold ocean currents make nearby coastal regions cooler.
tropical storms
Oceans play a critical role in the development of some of the earth's wildest storms. Hurricanes always form over ocean water that has a temperature of at least 80° F. Hurricanes usually start when a cluster of thunderstorms move across the ocean. Sometimes the low atmospheric pressure that occurs because of the warm water temperatures combines with the dense, humid air of the thunderstorms, which causes the air in the atmosphere to begin spinning. When this happens, it is called a tropical storm. About 5 percent of tropical storms become so powerful that they are classified as tropical cyclones. Storms like this which affect the US usually originate in the Atlantic Ocean and are called hurricanes. However, when these types of storms occur in the western Pacific Ocean, they are called typhoons. When they occur in the Indian and Southern Pacific oceans, they are called cyclones. Tropical cyclones always have an "eye" of calm winds and low pressure surrounded by high winds and high pressure.
precipitation
Precipitation is another facet of the hydrosphere that impacts climates. Clouds, rain, snow, sleet, and hail are all part of the hydrosphere. Most water vapor that becomes precipitation is evaporated from the oceans, though smaller amounts also come from rivers, lakes, soil, and vegetation. The amount of precipitation an area receives greatly determines its climate. Desert areas receive very little precipitation, whereas rainforests receive a great deal of precipitation. In general, low pressure areas receive more precipitation while high pressure areas receive less precipitation.
Is cold ocean water a factor in the creation of hurricanes?
Ocean water must be warmer than 80° F for a hurricane to form.
Where do hurricanes, cyclones, and typhoons always start?
on the oceans
Do high pressure zones generally receive the most precipitation, or do low pressure zones?
Low pressure zones usually receive the most precipitation.
How does the motion of currents moderate ocean temperatures?
The water moves between the polar and equilateral regions. It warms as it moves through the tropics and cools in the polar regions.
Describe ocean currents.
The currents are like rivers running through the oceans. They usually flow in a circular pattern. In the Northern Hemisphere the currents rotate clockwise, and in the Southern Hemisphere they rotate counterclockwise.
How does La Niña affect the weather?
During La Niña, many areas receive less rain than usual.
What is the difference between a hurricane and a cyclone?
Cyclones form in the Indian and Southern Pacific oceans; hurricanes form in the Atlantic.
What event occurs when the eastern Pacific Ocean is warmer than normal?
El Niño
How do oceans influence coastal temperatures?
Water does not heat and cool as rapidly as the air, so the oceans stay about the same temperature year-round. The temperature of the water affects the air.
latitude
As you will recall, the lithosphere is the solid part of the earth. It includes landforms like mountains and valleys. Landforms have a big influence on an area's weather and climate. You may not have thought about it before, but the location of a landform is probably the greatest factor to consider when it comes to determining the weather and climate of an area. As you learned earlier in the lesson, temperature can be affected by latitude. Landforms that are near the equator receive more solar energy than do landforms that are closer to the poles. The more solar energy an area receives, the warmer that area is. Can you find Australia on Figure 4.3.1? Now locate Greenland. Based on what you know about the relationship between temperature and latitude, what assumptions can you make about these two locations? Could you say that Australia is probably warmer than Greenland? Since Australia lies considerably closer to the equator than does Greenland, it is safe to assume that Australia is warmer.
precipitation-lithosphere affect
Another way that the lithosphere affects climate is its impact on precipitation levels. The shape of the lithosphere has a big influence on which areas receive precipitation. Look at Figure 4.3.2; the map shows precipitation levels in the US. Use the legend to find the areas that receive the most rain. On the east side of the country, notice how far inland the precipitation levels remain relatively high. Now look at the western side of the country. The northwest coast receives a significant amount of rain, but the pattern does not extend very far inland. What do you think explains this? One large factor is the mountainous nature of the western US.

Deserts are often caused by the orographic effect, which is the cooling effect that happens when air is forced to rise so that it can go over a mountain. As the air rises, the water vapor condenses and precipitation occurs. This means all of the water gets dumped on one side of the mountain, creating a humid environment, and by the time the air reaches the other side of the mountain it no longer has any water vapor left in it. This creates a desert.

Look at Figure 4.3.2 again. Notice how there is a dividing line down the continent where the dry desert air meets the humid air coming up from the Gulf of Mexico. The terrain across the central plains slopes downward from the Rocky Mountains towards the east. This slope makes a nice corridor for the dry air coming off the mountains to flow east. To the south, the Gulf of Mexico produces moist air that flows north. When the dry and moist air meet, a boundary line forms. It is along this line that a perfect environment sometimes exists for the creation of tornadoes. The area is often called Tornado Alley. There are more tornados in the US than anywhere else in the world because it has the right combination of terrain, water, and wind currents.
orographic effect
Deserts are often caused by the orographic effect, which is the cooling effect that happens when air is forced to rise so that it can go over a mountain. As the air rises, the water vapor condenses and precipitation occurs. This means all of the water gets dumped on one side of the mountain, creating a humid environment, and by the time the air reaches the other side of the mountain it no longer has any water vapor left in it. This creates a desert.
elevation
Another way that the lithosphere affects climate is elevation, or the height of the earth's surface above sea level. Areas with lower elevation usually have warmer temperatures than neighboring areas with higher elevation. It is usually colder on a mountain top than it is in the valley below. It can be warm at the foot of a mountain while the top of the mountain is covered with snow.

One of the hottest places on the face of the earth is Death Valley in California. The valley's average summer temperatures are over 100° F. One of the factors leading to the extreme heat is the valley's elevation. It is situated 282 feet below sea level. The low elevation and the valley's location cause the area to receive very little rain, averaging less than two inches per year.
Find Finland and India in the Figure below. Based on the latitude of the two countries, what assumption can you make about their climates?
Based on the latitude, Finland is probably colder than India
What is the orographic effect?
The orographic effect occurs when air is forced to rise so that it can go over a mountain. As the air rises and cools, the water vapor condenses and precipitation occurs. This means all of the water gets dumped on one side of the mountain, creating a humid environment; by the time the air reaches the other side of the mountain it no longer has any water vapor left in it, and this creates a desert.
What are three factors of Tornado Alley that lead to the formation of tornados?
The three factors that make Tornado Alley perfect for tornado formation are terrain, water, and wind currents.
Is it usually warmer or colder at high elevations?
It is usually colder at high elevations.
What blocks the humid air in eastern US from reaching the western US?
The mountains in the west block humid air from much of the western US.
What factor has the greatest influence on climate?
location
Landforms that receive the most solar energy are located where on the earth?
Equatorial landmasses receive the most solar energy.
Since altitude and latitude both have a big impact on climate, explain the difference between the two.
Altitude refers to the elevation of an object above sea level; mountains have high altitudes and valleys have lower altitudes. Latitude refers to the location on the earth; high latitudes are near the poles and low latitudes are near the equator.
greenhouse effect
There is concern that humans may be influencing the biosphere in other ways. You have probably heard of the greenhouse effect; this is a process that traps heat in the atmosphere. Without this process it would be too cold on Earth to live. In lesson 3 you learned about Venus. Do you remember that Venus' atmosphere is very thick and hot? This is because the atmosphere on Venus is made mostly of carbon dioxide.
Carbon DIoxide
is particularly good at trapping heat and is a major factor in producing the greenhouse effect.
global warming
There is concern that humans may be influencing the biosphere in other ways. You have probably heard of the greenhouse effect; this is a process that traps heat in the atmosphere. Without this process it would be too cold on Earth to live. In lesson 3 you learned about Venus. Do you remember that Venus' atmosphere is very thick and hot? This is because the atmosphere on Venus is made mostly of carbon dioxide. Carbon dioxide is particularly good at trapping heat and is a major factor in producing the greenhouse effect.

Many scientists are worried because burning products such as coal, natural gas, and oil adds carbon dioxide to the atmosphere. Since carbon dioxide absorbs heat, the atmosphere may become warmer and disrupt the normal climate and weather patterns. Since the late 1800s the level of carbon dioxide in the earth's atmosphere has increased by 30 percent. During the past century, the average temperature of the earth has increased by 1° F. If the increase continues, some scientists fear that there could be serious and permanent consequences. The warmer weather could cause polar caps to melt, which would cause sea levels to raise. During the last hundred years it is estimated that warmer temperatures have caused the sea level to rise four to eight inches. The warmer water may cause other problems too. As you learned earlier, tropical storms begin over warm ocean water. Scientists worry that warmer oceans could result in more frequent and stronger tropical storms. In the U.S. that could mean more hurricanes.

Some scientists believe that there has always been a natural cycle of global warming and cooling, and they are not convinced that human activities can alter the cycle. Scientists are working to determine exactly what the consequences might be if we continue to add large amounts of carbon dioxide to the atmosphere.
How much has the earth's average temperature increased during the last century?
The earth's temperature has raised 1°F.
Do all scientists agree that carbon dioxide emissions created by humans are changing the weather cycles?
Some scientists believe the warming trend is part of a natural cycle.
What did the US government do to help solve the problem? -The Dust Bowl
The US government paid farmers to implement new farming techniques to solve the problem of dust storms.
Which planet's atmosphere is composed largely of carbon dioxide?
Venus' atmosphere is composed largely of carbon dioxide.
How did the invention of the tractor influence the weather of the early 1900s?
Tractors enabled farmers to plow under large amounts of prairie sod; this activity led to severe dust storms.
What impact do some scientists predict global warming will have on the earth?
Many scientists predict that global warming could cause the following; polar caps could melt, sea levels could rise, and warmer ocean water could result in more frequent and stronger hurricanes. In some areas, deserts could become larger.
How much of an increase in atmospheric carbon dioxide levels has occurred in the last one hundred years?
Carbon dioxide levels in the atmosphere have risen 30 percent.
What has happened to the level of the sea due to the increase in temperature?
The sea has risen between four and eight inches.
What is the greenhouse effect?
The greenhouse effect is the process that traps heat in the atmosphere.
Can the biosphere change weather patterns?
Yes, the biosphere can change weather patterns. Humans are members of the biosphere and they have influenced weather patterns in the past.
What are some examples of products that, when burned, add carbon dioxide to the atmosphere?
Oil, gas, and coal produce carbon dioxide emissions.
low latitude climates
The first group we will look at is the low latitude climates. Remember that the equator is 0° and this is the lowest latitude that exists, so the lower the latitude of a location, the closer it is to the equator. Because low latitudes are near the equator, the low latitude climates are warm climates. There are three major subgroups in this group.
tropical moist climates
The first subgroup is tropical moist climates. This is the climate of a beach vacation. The African Congo and the Amazon in South America also share this climate. You can expect rain almost every day in this climate, but the average temperature is about 80° F year-round.
wet-dry tropical climate (savannah)
The second subgroup is the wet-dry tropical climate, or the savannah. These areas have a wet season and a dry season. You might expect that it would be warmer during the dry season, but the wind blows from the higher latitudes during that time so the dry season is a little cooler. India, West Africa, and the northern coast of Australia are some of the areas that have this climate.
dry tropical climate
The third part of the low latitude climates is the dry tropical climate. These are hot, dry areas or deserts. The southwestern United States, South Africa, Argentina, and the Arabian Peninsula are some areas that experience this type of climate.
high latitude climates
This climate is located in the high latitudes of the northern hemisphere. Parts of Canada and Siberia fall into this category, and as you might guess, the temperature is often cold. There are both humid and arid areas in this climate zone, but the climate is characterized by very long winters and short periods of warmer weather.
polar climates
The coldest climates on Earth are the polar climates in the polar regions. The north and south polar regions are really quite different from one another. The Arctic (in the north) is made of an ice cap sitting in the middle of the Arctic Ocean. In the summer months, as the temperature increases, the cap melts slightly around the edges. At the opposite end of the world sits Antarctica, and as you probably know, Antarctica is a not just an ice cap, but is instead a continent. The North Pole sits in the center of the Arctic, and the South Pole sits in the center of Antarctica. Which pole do you think gets colder? Remember that areas which are surrounded by water are more temperate than areas deep within a continent. This means that it is colder at the South Pole than it is at the North Pole. The coldest temperature ever recorded on Earth was at the South Pole where it was once -128.6° F.
Mid-latitude Climates
highland, dry midlatitude
highland climate
This climate is found in the mountains of the midlatitudes. The highland climates are cool to cold, depending on the altitude; the higher the altitude, the colder the temperature. The highlands have the same seasons and the same wet and dry periods as the general area that they are located in. For instance, the mountains in desert areas receive little rain, and the mountains in humid areas receive a lot of rain. When it is winter in Utah, it is winter in the High Uintas (a wilderness area southeast of Salt Lake City), and when it is summer in Utah the temperature warms up in the High Uintas. Highland climates are found in the high elevations of the Rocky Mountains, the Andean mountain range in South America, the Alps in Europe, Mt. Kilimanjaro in Africa, the Himalayans in Tibet, and Mt. Fuji in Japan.
dry midlatitude climates
There are also the dry midlatitude climates. These are the lower elevation areas situated between 35° and 55° latitude. There are really two different dry midlatitude climates: the steppe climate and the grassland climate. The steppe climate is not quite a desert since it receives some moisture, but it is quite dry and usually receives somewhere between four and twenty inches of precipitation each year. Look at the US precipitation distribution in Figure 4.3.2. Find the areas that receive four to twenty inches of rain. As you can see, most of the western side of the US has a steppe climate. The grassland climates receive a little more rain, usually about thirty-two inches per year. Look at the map again and find the areas that receive between twenty and thirty inches of rain. As you can see, the US has a narrow band of grassland climate. Europe and northern China are other areas that have dry midlatitude climates.
steppe climate
The steppe climate is not quite a desert since it receives some moisture, but it is quite dry and usually receives somewhere between four and twenty inches of precipitation each year. Look at the US precipitation distribution in Figure 4.3.2. Find the areas that receive four to twenty inches of rain. As you can see, most of the western side of the US has a steppe climate.
grassland climate
The grassland climates receive a little more rain, usually about thirty-two inches per year. Look at the map again and find the areas that receive between twenty and thirty inches of rain. As you can see, the US has a narrow band of grassland climate. Europe and northern China are other areas that have dry midlatitude climates.
The Mediterranean Climate
The Mediterranean climate is also found in the midlatitudes. This climate has a very long, dry summer with a wet winter. Like the steppe, the Mediterranean climate is not quite a desert, but it is still quite dry, usually receiving only about seventeen inches of rain per year. The biggest difference between the Mediterranean and steppe climates is the temperature. This is because Mediterranean climate zones are located along coastal regions and receive the moderating influence of ocean currents, so there is not a wide range between winter and summer temperatures. As you might expect, the Mediterranean climate is found along the coastal zones of the Mediterranean Sea in Europe, as well as in central and southern California. Western and southern Australia and the Chilean coast in South America also have Mediterranean climates.
The moist continental climate
The moist continental climate is the last midlatitude climate subgroup we will consider. This area is also between 35° and 55° latitude, but it lacks mountain ranges to block the air masses so polar and tropical air are constantly clashing. Unlike the Mediterranean climate, the seasonal changes experienced in this climate are quite dramatic. The winters are cold and the summers are hot. Even daily temperatures change often, and there is abundant precipitation. The eastern portion of the US falls into this climate zone, as does Korea, Japan, and Eastern Europe.

As you have read about climates, you might have noticed that most of the climates we have looked at are in the Northern Hemisphere. This is because more of the earth's landmass is located in the Northern Hemisphere.
low latitude climates
tropical moist climate, wet-dry tropical climate, dry tropical climate
midlatitude climates
highland climate, Mediterranean climate, moist continental climate
steppe and grassland
dry midlatitude climate
midlatitude climate with dramatic seasonal changes
moist continental climate
biggest difference between Mediterranean and steppe climates
cold winter weather for one and not the other
coldest climate on Earth
polar climates
biggest difference between the steppe and the grassland
one receives more water than the other
location of highland climates
Alps or Rocky Mountains
climate that receives rain almost every day
tropical moist climate
dry tropical climate
desert
human settlements and the weather
alters precipitation levels, temperature, and causes sever weather
About how many tornados were there in Florida during 1983?
85
In which year did the greatest number of deaths due to tornados occur in Florida?
1962
About how many people were killed by tornados that year? 1962
about 18
Do the areas with a low population density occur more in areas of high precipitation or low precipitation?
The correct answer is: Areas of low population occur more in areas of low precipitation.
Do more people live in high latitudes or midlatitudes?
More people live in the midlatitudes.
How are mountain climates important in the midlatitudes?
Mountains store water as snow; as the snow melts it provides water.
Is it accurate to say that people are less likely to settle where there are severe weather patterns such as hurricanes and tornados?
Settlement patterns are not greatly affected by severe weather patterns.
Are populations generally more dense in coastal areas or inland?
Populations are generally denser in coastal areas.
Which factor that often determines climate might explain the population pattern of Michigan?
The population of Michigan lives mostly in the lower latitudes of the state.
Which factor probably has the greatest impact on the temperatures of both South Dakota and Michigan?
Michigan and South Dakota are located at about the same latitude.
What event occurs when the eastern Pacific Ocean is warmer?
El Niño
Where are highland climates located?
midlatitudes
What type of air pressure typically occurs in the polar regions?
...
What changes have occurred in the earth's climate in the last century?
Temperatures have increased; ocean levels have increased.
Find the Isthmus of Panama and the Malay Peninsula on the map. Based on what you know about latitudes, climates, and oceans, what assumptions can you make about these two locations?
Both areas have moist climates.
Find North Dakota and Italy on the map. Based on what you know about latitudes, climates, and oceans, what assumptions can you make about these two locations?
There is less variation of temperature in Italy than in North Dakota.
Find Madagascar and Cape Horn on the map. Based on what you know about the relationship between climate and latitude, what assumptions can you make about these two locations?
Madagascar has a warmer climate than Cape Horn.
Wind is
horizontally flowing air
What is the greenhouse effect?
the process that traps heat in the atmosphere
What conclusions might we draw by comparing the two maps? Q. 18
More people live in wetter climates.
19. Which part of the state is the most humid?
eastern
20. In which part of the state are more of the heavily populated counties found?
eastern
Which statement describes carbon dioxide levels in the earth's atmosphere?
Carbon dioxide levels have increased by 30 percent in the past century.
Which areas generally receive the most precipitation?
low pressure zones
Where do more people live?
midlatitudes
How do oceans influence coastal climates?
Water temperatures do not change rapidly, which moderates the air temperature.
How did the biosphere impact the weather in the American Midwest in the 1930s?
Farmers plowed too much prairie sod.
Where are hurricanes and cyclones most likely to form?
Hurricanes form in the Atlantic Ocean; cyclones form in the South Pacific.
How are the Mediterranean and grasslands climates different?
The grasslands climate has colder winter seasons and receives more precipitation than the Mediterranean climate.
Which climates are found in the low latitudes?
tropical moist, wet-dry tropical, dry tropical
Which midlatitude climate is humid and has dramatic seasonal changes?
moist continental
Objectives:


ID

Mastery

Description

4.1




Describe ways the atmosphere impacts the climate and weather.
4.2




Describe ways the hydrosphere impacts the climate and weather.
4.3


Describe ways the lithosphere impacts the climate and weather.
4.4


Describe ways the biosphere impacts the climate and weather.
4.5




Identify climate types.
4.6


Compare the impact of weather on human settlement patterns.
4.7




Create and interpret maps.
4.8




Identify Illinois, Indiana, Iowa, Kansas, Louisiana, Missouri, and Nebraska on a map.
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