Air environment Study Guide

AIR ENVIRONMENT STUDY GUIDE

The atmosphere is a blanket of air made up of a mixture of gases that surrounds the Earth.  It reaches almost 350 miles from the surface of the Earth.  It is constantly in motion.  Life on Earth is supported by the atmosphere, solar energy, and the planets magnetic fields.  The atmosphere absorbs energy from the Sun, recycles water, and provides a moderate climate. The atmosphere also protects life on Earth from high energy radiation and the frigid vacuum of space. 

COMPOSITION OF THE ATMOSPHERE

In any given volume of air, nitrogen accounts for 78% of the gases that comprise the atmosphere, while oxygen makes up 21%. Argon, Carbon Dioxide, and traces of other gases make up the remaining 1%.  A variable amount of water vapor can also be present.  That little bit of vapor is responsible for a lot of changes in our weather. 

ATMOSPHERIC LAYERS

There are five distinct layers of atmosphere.  They are defined by changes in temperature, physical, and chemical properties. 

Troposphere

This is the first layer, next to the Earth.  It extends up to 20,000 ft over the poles and 55,000 feet over the equator.  MOST OF THE ATMOSPHERE IS CONTAINED IN THIS REGION.  The vast majority of  weather, clouds, storms and temperature differences occur here. In the troposphere, the higher you go, the colder it gets.  Its is a very consistent change.  The Lapse Rate is a temperature decrease of 2^o C for every 1,000 foot increase in altitude. At the top of the Troposphere is a boundary called the TROPOPAUSE, which divides the Troposphere from the Stratosphere. 

Stratosphere

The next layer of atmosphere is the stratosphere. This layer extends from the Tropopause, to approximately 160,000 ft or 30 miles.  There is very little weather in this layer.  The air in this layer is stable except for certain types of clouds that occasionally exist there.  In this layer the temperature gets warmer the higher you go.  However, it is still pretty cold!!  The temperature increases from about -76^o C to -40^o C. The U-2 plane often flies in the stratosphere. At the top of the stratosphere is the Stratopause, the boundary between the stratosphere and mesosphere. 

Mesosphere 

This layer of atmosphere extends from  the stratopause  to about 280,000 feet.  It exists from about 30 to 50 miles about the Earth.  In this layer, first the temperature increases, but then at the top decreases to -130^o F. The Mesopause is the boundary between the Mesosphere and the Thermosphere.

Thermosphere

It begins about 50 miles up and extends to about 300 miles.  Here the temperature ranges widely from absolute zero, to very hot, 1,380^o F to 2,280^o F. The Thermopause marks the top boundary of the thermosphere. 

Exosphere

This is a thin atmosphere like layer where the volume of molecules is so low they are essentially collision less. It thins out and merges with outer space. It is mostly composed of Hydrogen, Helium, carbon dioxide, and oxygen.  It ranges from 310 to 600 miles above the Earth. The upper boundary is where the Sun has more influence over the Hydrogen atoms than the Earth. The temperature depends on how much solar activity there is. 

ATMOSPHERIC REGIONS

There are two REGIONS of atmosphere that overlap the LAYERS of atmosphere.  They are defined by chemical processes that occur within them.

OZONOSPHERE

This region extends from about 10 to 30 miles in altitude, so it is in the stratosphere.  In this region the suns radiation reacts with oxygen molecules and causes them to pick up a third atom, creating OZONE- a layer of molecules that shield us from the ultraviolet and infrared radiation from the Sun.  Without this layers the Earths surface would be sterilized of life by UV radiation. Breakdown of the Ozone causes cancer in humans and animals, as well as cataracts, and interferes with the photosynthesis of phytoplankton, the producer and foundation of the ocean food web. In the winter and spring every year, the ozone layer thins over Antarctica.  It was discovered in the 1970's that human made products with chlorofluorocarbons (CFCs) used in aerosol spray cans and refrigerators, reacted with the Ozone layer increasing the thinning process.  Every country on Earth signed the Montreal Protocol  chlorofluorocarbons (CFC's). The Ozonosphere

is doing better today.

  . 

THE IONSOPHERE

The ionosphere starts at about 25 miles and extends to around 250 miles.  The reaction of atmospheric particles with the Suns radiation lead to the loss or gain of electrons.  This layer is where a person can see the aurora borealis and the aurora australias.  The Borealis is seen more often the closer one gets to the arctic, the australias is seen the closer one gets to the Antarctic. 

The lights we see in the night sky are in actual fact caused by activity on the surface of the Sun.

Solar storms on our star's surface give out huge clouds of electrically charged particles. These particles can travel millions of miles, and some may eventually collide with the Earth.

Most of these particles are deflected away, but some become captured in the Earth’s magnetic field, accelerating down towards the north and south poles into the atmosphere. This is why aurora activity is concentrated at the magnetic poles.

These particles then slam into atoms and molecules in the Earth’s atmosphere and essentially heat them up,” explains Royal Observatory astronomer Tom Kerss. “We call this physical process ‘excitation’, but it’s very much like heating a gas and making it glow.”

What we are seeing therefore are atoms and molecules in our atmosphere colliding with particles from the Sun. The aurora's characteristic wavy patterns and 'curtains' of light are caused by the lines of force in the Earth’s magnetic field.

AIR CIRCULATION

The sun heats the Earth and is the fundamental cause of our various weather conditions.  Because the Sun heats the Earth unequally, there are temperature and pressure differences from one area of the Earth to another. This creates movement of air and it creates Weather. 

Radiation

The Sun heats the Earth by a method called radiation.  The energy from the Sun radiates into the Earths atmosphere, and finally reaches the Earth itself.  Fifty-one percent of the Suns radiation is absorbed by the Earths surface.  The other 49% is reflected, absorbed in the atmosphere and space.  

Warm air rises.  The rising warm air adds to temperature and pressure differences, as well as air movement.  The rising air effects the surrounding air masses and fronts.  It helps create clouds and plays a part in precipitation.  

Rotation and Revolution

The Earth has two motions that affect the amount of heat received from the Sun.  These two motions are rotation and revolution.

The Earth revolves around the Sun. At the same time, the Earth rotates on its axis.  An axis is an imaginary straight line around which an object spins.  Its axis is tilted at an angle of 23.5 degrees, and stays tilted in the same direction as it revolves around the Sun. This rotational tilt causes the length of the days to vary and the rotation plus the revolution causes the seasonal changes. The Earth spins one complete turn every 24 hours. The Earth revolves around the Sun every 365 days, 5 hours and 48 minutes. 

In the summer in the Northern Hemisphere ( where we live) the axis is tilted toward the sun and the suns radiation is more directly hitting the Earth at its highest point above the equator. June 21 or 22 is known as the summer solstice and is the longest day of the year. In winter the axis is pointed away from the sun.  On December 21 or 22nd we have the winter solstice, which is the shortest day of the year.  We have two days a year, where we have days and nights of equal length.  These days are called Spring Equinox and Fall Equinox.  

Circulation and Global Winds

Unequal heating causes air movement. This is Wind.  Global Winds are a world wide wind system that transfers heat between tropical and polar regions.  The region of Earth that receives the majority of the Suns radiation is the equator.   At the equator air is heated and it rises.  This is because the air molecules become more active and less dense as they are heated.  As the air rises it leaves low pressure areas behind it.  It rises and moves to about 30 degrees latitude North or South, where it begins to cool and sink.  Some of the air cools,  sinking, and moving  back toward the equator. .  The Air movement toward the equator is called the TRADE WINDS- warm, steady breeze's that blow almost continually.   Trade winds from 30 degrees north and south blow toward the equator and meet.  The converging trade winds produce upward winds as they are heated, so at the equator there are no steady winds.  DOLDRUMS- the area of calm at the equator. 

Westerlies

Between 30 and 60 degrees latitude, more air is heated and rises. These winds bend toward the East.  WE NAME WIND FOR THE DIRECTION IT COMES FROM, so these winds that head East are called Prevailing Westerlies, for where the wind comes from.  At about 60 degrees latitude the prevailing westerlies meet the prevailing easterlies.  Cold air sinking at the poles, spreads south and west.  Because it comes from the the East, these winds are called the Easterlies.  The same thing is happening in the Southern Hemisphere.  

Jet Stream

A Jet Stream is a river of air that crosses the US at about 30,000 to 35,000 feet, moving from west to east.  It develops in the upper troposphere where there are strong temperature  and pressure differences, creating strong winds.  The jet streams winds are generally 100 to 300 miles per hour, with highest speeds recorded at 450 miles per hour.  It moves like a winding road across the US, thousands of miles long, hundreds of miles wide, and a few miles deep.   It is stronger and dips farther south in the winter.  Pilots use the jet stream to improve fuel consumption and speed when flying west to east across the country. There is a polar jet stream and a subtropical jet stream in the Northern hemisphere.  There are jet streams in the southern hemisphere as well.