Atmosphere

Reading: Textbook Chapter 22 p.

Characteristics of the Atmosphere

There are two main gases in the atmosphere, nitrogen about 78% and oxygen about 21%. The layer closest to the Earth is called the troposphere. Almost all weather occurs in the troposphere. The troposphere gets cooler with increasing altitude. Temperatures drop about 6 degrees C/ km. The ocean and ground absorbs solar energy making it warmer in lower altitudes. Air at higher altitudes is less dense and is not as close to heat sources. Commercial airlines travel in the troposphere and stratosphere.

Stratosphere is the layer immediately above the troposphere. The stratosphere gets warmer with the increasing temperature, notice the red line in the picture above showing the change in temperature. The increase in temperature in the upper stratosphere occurs in the atmospheric layer known as the ozone layer. The ozone layer is warmer because it contains a form of oxygen called ozone that absorbs solar radiation. The oxygen that we breathe contains two oxygen atoms, but ozone molecules contain three oxygen atoms. The ozone layer shields life on Earth's surface from ultraviolet-radiation damage.

Mesosphere is the coldest layer of the atmosphere. Fighter jets are able to fly in the mesosphere. Temperatures again rise in the next layer of the atmosphere called the thermosphere. Satellites orbit the Earth in the thermosphere. Some gases escape the gravitational pull of Earth and travel out into space in the thermosphere.

The outer most layer of the atmosphere described by our book at part of the thermosphere is called the exosphere.

An area of electrically charged ions that form between the thermosphere and the mesosphere is called the ionosphere, but it is not a separate layer of the atmosphere. The ionosphere is used in radio communications. The ionosphere is where auroras, a colorful light display, take place. This is caused by energetic ions from the sun hitting atoms and molecules of gas in the ionosphere causing photons to be emitted.

 

Auroras occur most often in the north over Alaska, shown in the top picture, and in Australia, in the picture directly above.

This photo was taken in Oklahoma after an electrical storm.

The Earth's Atmosphere is always changing.

Volcano eruptions released a variety of gases into Earth's early atmosphere. Most of the gases would have been poison to us today. Photosynthetic plants evolved around 2.5 billion years ago that contributed to oxygen in the atmosphere. The amount of these plants change the level of oxygen in the atmosphere. About 350 million years ago, the concentration of oxygen reached a level close to what it is today. Animals produce carbon dioxide necessary for photosynthesis. These process or natural reoccurring processes. Man-made chemicals also affect the atmosphere. These chemicals can deplete the ozone layer allowing harmful ultraviolet-radiation to reach Earth. Layers of atmosphere gases act as a blanket for the Earth trapping the heat from the sun. This is called the greenhouse effect. Increased levels of carbon dioxide, from burning coal, oil, and gas power plants, machinery, and cars, may lead to global warming.

Water and Wind

The water cycle is the continuous movement of water from the ocean to the atmosphere to the land and back to the ocean.

Evaporated water vapor condenses to form precipitation. Transpiration is the process by which plants release water vapor into the air through stomata. Air contains varying quantities of water vapor. Humidity is the quantity of moisture in the atmosphere. Warmer temperatures evaporate more water. Water vapor becomes liquid at dew point, the temperature at which gas begins to condense to a liquid. Dry air is heavier than moist air. Water molecules are mainly hydrogen which is the lightest element. Dry air is mostly oxygen which is 8 times heavier than hydrogen. Clouds form as warm, moist air rises. Clouds names describe their shape and altitude.

• Cirrus - thin and wispy, high altitude
• Stratus - sheet-like and layered, lower altitudes
• Cumulus - white and fluffy, flat bottom, varying altitudes

Clouds names reflect combined characteristics. Nimbo or nimbus means produces precipitation. So cumulonimbus or towering fluffy clouds with flat bottoms that produce thunderstorms.

Explore cloud types and the weather the cause.

Barometric (air or atmospheric) pressure is often used in weather reports. Changes in barometric pressure often accompany changes in weather. Barometers are the instruments used to measure air pressure.

Differences in air pressure create winds. Airflow moves from areas high-pressure to areas of low-pressure. Earth's rotation affects the direction of winds. Coriolis effects is the curving of the path of a moving object from an otherwise straight path due to Earth's rotation. Predictable air circulation forms wind patterns. Global wind patterns form circulation cells. Winds in the Northern Hemisphere curve clockwise and winds in the Southern Hemisphere curve counterclockwise.

Weather and Climate

Large body of air where temperature and moisture content are similar throughout are called air masses. Interaction between air masses have predictable effects on the weather in a given location. A front is a boundary between air masses of different densities and usually different temperatures.

There are three types of fronts.

1. warm front - warm air moves toward and over a slower mass of cold air, causing the air to cool and form clouds. Nimbostratus clouds form bring rain or snow that last for one to two days.
2. cold front - mass of cold air moves under a slower mass of warm air and pushes it up, creating high cumulonimbus clouds that bring high winds, thunderstorms, and tornadoes.
3. stationary front - two air masses meet but neither is displaced.

 

Lightning is a discharge of atmospheric electrical energy caused by the friction as particles of water droplets and ice crystals rub against each other.

Tornadoes are funnels of high-speed winds caused from warm air quickly rising and cool air rushing in to take its place.

Explore tornado rating scale.

Climate is the average weather conditions in an area over a long period of time. Temperatures tend to be higher close to the equator creating a warm climate. Earth's tilt and rotation account for our seasons.

 

An ecosystem is the community of organism and their environment. The organisms that live in an environment cause changes to the ecosystem, therefore having an affect on the atmosphere of the whole planet.

A change in the number of one organism can increase or decrease the number of another organism.

Man has the greatest affect on Earth. Clearing trees, driving cars, constructing building, pollution, waste treatment, and farming has a significant affect on the environment.