Unit 1 – The Basics of Geography

Unit 1 – The Basics of Geography

Chapter 3Climate and Vegetation

Page 49

What causes seasons?

The earth revolves around the sun with a 23.5 degree tilt in relation to the sun.

Because of the earth’s revolution and its tilt, different parts of the earth receive the direct rays of the sun for more hours of the day at certain times of the year.

Two lines of latitude mark the points farthest north and south that the sun’s rays shine directly overhead at noon. These two lines are the tropic of Cancer and the tropic of Capricorn.

Solstice – either of two times of year when the sun’s rays shine directly overhead at noon at the furthest points north or south, and that mark the beginning of summer and winter. In the Northern Hemisphere, the summer solstice is the longest day and the winter solstice is the shortest.

Equinox – each of the two days in a year on which day and night are equal in length; marks the beginning of spring and autumn.

The two terms weather and climate are often confused with one another.

Climate – weather conditions at a particular location over a long period of time.

Weather – is the condition of the atmosphere at a particular location and time.

What causes the weather?

Water vapor determines if there will be precipitation – falling water droplets in the form of rain, sleet, snow, or hail.

Cloud cover may hold water vapor.

Landforms and bodies of water. Land heats rapidly but loses heat quickly as well while water heats slowly but also loses heat slowly.

Elevation- As elevation above sea level increases, the air becomes thinner and loses its ability to hold moisture.

Air movement – Winds move the air and the solar energy and moisture that it holds. As a result, weather can change very rapidly.

What does precipitation depend upon?

Precipitation depends on the amount of water vapor in the air and the movement of the air.

Water vapor condenses, forms droplets, and becomes a cloud.

When the amount of water in a cloud is too heavy for the air to hold, precipitation falls.

Convectional Precipitation

Typical of hot climates, convection occurs after morning sunshine heats warm, moist air. Clouds form in the afternoon and rain falls.

Orographic Rainfall

Associated with mountain areas, orographic storms drop more rain on the windward side of a mountain and create a rain shadow on the leeward side.

Rain Shadow – land on the leeward side of a mountain which gets little rain from descending, dry air.

Frontal Rainfall

Mid-latitude frontal storms feature cold, dense air masses that push lighter, warm air masses upward, causing precipitation to form.

What are examples of weather extremes?

• Hurricanes• Tornadoes• Blizzards• Droughts• floods

Hurricanes – Storms that form over warm, tropical ocean waters

Other names for hurricanes across the world

Typhoons-AsiaWilly-willies-AustraliaBaguios-PhilippinesChubascos-Mexico

Hurricanes allow heat from the tropics to be moved out of an area.

Tornado – a powerful funnel-shaped column of spiraling air. It’s also known as a twister.

Tornadoes are usually born from strong thunderstorms.

The largest outbreak of tornadoes in the United States occurred during a 16-hour period, April 3 and 4, 1074. A total of 148 tornadoes killed 330 people across Ohio and Tennessee.

The National Weather Service counts about 700 tornadoes every year.

Blizzard is a heavy snowstorm with winds of more than 35 miles per hour and highly reduced visibility.

The greatest snowfall for a 24-hour time period was 76 inches in Silver Lake, Colorado in 1921.(six feet, four inches)

Drought – is a long period of time without rain or with very minimal rainfall.

Droughts cause crop failures and reduced levels in water storage areas.

In the 1930s, drought conditions were so bad that a 150,000 square mile area was known as the “Dust Bowl.”

Flood – when water spreads over land not normally covered with water.

Flood Plains – areas prone to flooding.

What four major factors influence the climate of a region?

1. Wind and ocean currents

2. Latitude3. Elevation4. Topography

Wind Currents

Wind and ocean currents help move the sun’s heat from one part of the world to another through convection.

Convection – the transfer of heat in the atmosphere by upward motion of the air

Ocean currents are like rivers flowing in the ocean. Warm water flows away from the equator toward the poles, and cold water flows back toward the equator.

Ocean currents affect not only the temperature of an area, but also the amount of precipitation received.

Zones of Latitude

Geographers divide the earth into three general zones of latitude.

What are the three general zones of latitude?

1. Low or tropical2. Middle or temperate3. High or polar

Elevation affects climate. The higher you go, the colder it gets.

Topography

Landforms also affect the climate. This is very true of mountain areas.

Changes in Climate

Climates can change over time. Scientists use ice-core samples from thousands of years past to study a variety of changes in temperature and precipitation.

Some of the changes in climate appear to be natural. Some may be the result of human activity.

El Niño – The warming of the waters off the west coast of South America

El Niño is a natural change in the climate. About every two to seven years, prevailing easterly winds that blow over the central Pacific Ocean slow or reverse direction, changing the ocean temperature and affecting the weather worldwide.

La Niña is the reverse.

Global Warming is a theory that believes the earth is heating up since the 1800s.

Greenhouse effect – the layer of gas released by the burning of coal and petroleum traps some solar energy, causing higher temperatures in the same way that a greenhouse traps solar energy.