Download Integrated Science Chapter 20 Notes Section 1: Characteristics of

Integrated Science
Chapter 20 Notes
Section 1: Characteristics of the Atmosphere
1. Layers of the Atmosphere
The atmosphere has several layers. These layers differ in temperature, density, and amount of
certain gases present. The layers of Earth’s atmosphere include:
• The troposphere – the atmospheric layer closest to Earth’s surface where nearly all weather
occurs
→ The troposphere is the densest of the layers
→ The troposphere gets cooler with increasing altitude
‰ The temperature decreases about 6oC for every kilometer of altitude
→ Temperature inversion – the atmospheric condition in which warm air traps cooler air near
Earth’s surface
→ The altitude of the troposphere is different at different places
‰ At the poles it occurs at around 8 km, while at the equator it rises to nearly 18 km
• The stratosphere – the layer of the atmosphere that extends upward from the troposphere to an
altitude of 50 km
→ The stratosphere contains the ozone layer
‰ Ozone – the form of atmospheric oxygen that has three atoms per molecule
‰ Ozone protects life on Earth from ultraviolet radiation
→ The temperature increases with altitude in the stratosphere
→ The stratosphere contains very little water vapor, so there are no clouds and very little wind
• The mesosphere – the coldest layer of the atmosphere; located above the stratosphere
→ The mesosphere extends from 50 km to 80 km above the surface
→ Temperature decreases with an increase in altitude
‰ At the top of the mesosphere the temperature is –80oC
• The thermosphere – the atmospheric layer above the mesosphere
→ Altitude ranges from 80 km to 480 km above the surface
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→ The average temperature of the thermosphere is around 980 C
• Ionosphere – the area in the upper mesosphere and lower thermosphere where electrically
charge ions are formed
→ The ionosphere is used for radio communications
‰ The electrons in the ionosphere reflect the radio waves back to Earth
‰ Without the ionosphere, the waves would continue out into space
→ The auroras occur in the ionosphere
2. Changes in the Earth’s Atmosphere
Since the formation of Earth around 4.6 billion years ago, the atmosphere has undergone many
changes. The original atmosphere was very different from what we know today, and would be
poisonous to us.
• Photosynthetic plants contribute oxygen to the atmosphere
→ Around 2.5 billion years ago some plants evolved a method of capturing energy from the sun
and converting it to sugar, which was used as a food. This processed produced oxygen as a
byproduct.
→ Over time enough oxygen was released by these plants to raise the level of oxygen in the
atmosphere to what it is today
• Human actions have also caused changes in the atmosphere
→ Manmade chemicals, mostly chlorofluorocarbons (CFCs), have depleted the protective ozone
layer allowing more ultraviolet radiation to reach the surface of Earth.
→ Greenhouse effect – the process by which the atmosphere traps some of the energy from
the sun in the troposphere
→
Carbon dioxide, water vapor, and other gases absorb heat and hold it close to the surface
‰ While some carbon dioxide is produced naturally, it is also present in the exhaust from
automobiles and coal and natural gas powered power plants
‰ This extra carbon dioxide in the atmosphere increases the greenhouse effect and leads
to global warming
Section 2: Water and Wind
1. The Water Cycle
• Water cycle – the continuous movement of water from the atmosphere to Earth and back
→ The major part of the cycle occurs between the oceans and the continents, and is powered
by energy from the sun
‰ Transpiration – the evaporation of water through pores in a plant’s leaves
‰ Precipitation – any form of water that falls back to Earth’s surface from clouds; includes
rain, snow, sleet, and hail
• Air contains varying quantities of water vapor
→ Humidity – the quantity of water vapor in the atmosphere
→ Relative humidity – ratio of the quantity of water vapor in the air to the maximum quantity of
water vapor that can be present at that temperature
→ Warmer temperatures evaporate more water
→ Dew point – the temperature at which water vapor molecules start to form liquid water
• Clouds form as warm, moist air rises
→ This process usually occurs in the troposphere
→ Water vapor condenses into droplets of liquid, and at higher altitudes, ice crystals
→ Clouds can have many different shapes and characteristics
→ Cloud names describe their shape and altitude
‰ The three main types of clouds are cirrus, stratus, and cumulus
‰ Cirrus clouds are thin and wispy and occur at high altitudes
‰ Stratus clouds are sheetlike and layered and typically form at lower altitudes
‰ Cumulus clouds are white and fluffy with flat bottoms and can form at various altitudes
2. Air Pressure
• Barometric pressure – the pressure due to the weight of the atmosphere
→ Also called atmospheric pressure or air pressure
• Air pressure is measured using a barometer
→ Two types of barometers: the mercury barometer and the aneroid barometer
→ Different units are used to measure air pressure
3. Wind
• Differences in pressure create winds
→ A pressure gradient exists wherever the air pressure varies
→ The air in the pressure gradient moves from areas of high pressure to areas of low pressure
→ This movement of air is the wind
• Earth’s rotation affects the direction of wind
• Coriolis effect – the change in the direction of an object’s path due to Earth’s rotation
→ In the Northern Hemisphere, the wind curves to the right
→ In the Southern Hemisphere the winds curve to the left
Section 3: Weather and Climate
Air mass – a large body of air with uniform temperature and moisture content
1. Fronts and Severe Weather
• Front – the boundary between air masses of different densities
→ Clouds, rain, and sometimes snow can occur
→ When a front moves through an area precipitation can occur along with a change in wind
direction and temperature
• Lightning is a discharge of atmospheric electrical energy
•
Tornadoes are funnels of high-speed winds
Wind speeds can occur as high as 500 km/hr (310 mi/hr)
• Hurricanes are large storm systems
→ Hurricanes are large circulating masses of clouds, wind, and rain with average diameters of
about 600 km
2. Weather Maps
• Meteorologists use weather maps to prepare weather forecasts
→ The maps use different symbols to show weather conditions such precipitation, wind speed
and direction, barometric pressure, and cloud coverage
→ Isobar – a line on a weather map connecting points of equal barometric pressure
‰ When the isobars form a closed loop, the center of the loop is called a pressure center
‰ Low pressure centers are areas where the air pressure is generally lower than the
surrounding areas
‰ These lows are often accompanied by clouds and precipitation
‰ High pressure centers usually mark regions of fair weather
→
3. Climate
• Climate – the general weather conditions over many years
→ Climate is the average weather or a region measured over many years
• Temperatures tend to be higher close to the equator
• Earth’s tilt and rotation account for our seasons
• Earth’s surface features affect climate
→ Topography – the surface features of Earth
• Global climate changes over time