Chapter 23 The Atmosphere Section 1 Characteristics of Atmosphere Notes 23-2

Atmospheric Pressure  Gravity holds the atmosphere next to the planet –If the gravity were less, there would be no atmosphere –99% of the total mass of atmosphere is within 32 km of the surface –The last 1% spreads upward and becomes very thin until you reach space

Atmospheric Pressure  Ratio of the force of the air to the area of the surface on which it presses –Less air at high altitudes means lower atmospheric pressures at high altitudes –When air pressure changes, it causes a popping sensation in your ear  Once the pressure is equal the popping stops  Happens when in an airplane or travel to higher altitudes in a car

Barometers  Instrument that measures atmospheric pressure –Mercurial Barometer:  Atmospheric pressure pushes on the liquid mercury in a well at the base of the barometer  Pressure squeezes the mercury up a tube  The tube is marked with readings  The higher the mercury, the higher the atmospheric pressure

Barometers  Expressed in how high the mercury rises  Standard atmospheric pressure = 760 mm –Equal to one atmosphere –Average atmospheric pressure at sea level is one atmosphere  Millibars (mb) are also used –1 mb = standard atmospheric pressure

Barometers  Aneroid Barometers: –Aneroid means without liquid –Sealed metal container with a vacuum inside  As pressure increases the sides push in  As pressure decreases the side pop out –The changes is marked by a moving pointer along a scale  Scale can be marked in mm, inches or mb –Also called an altimeter  Measures altitude above sea level

Layers of Atmosphere  As altitude increases, pressure decreases at a constant rate –Pressure changes don’t distinguish the different layers of the atmosphere –Temperature changes do separate the atmosphere into layers

Troposphere  Layer closest to the earth  Troposphere comes from the Greek word that means “change”  This is where all weather occurs –Almost all water vapor and carbon dioxide is found in this layer  Temperature decreases as altitude increases –Decreases at a rate of 6.5°C/km

Troposphere  Tropopause: –Zone between the troposphere and the next layer; upper boundary of troposphere –Temperature remains constant –Altitude on this boundary changes according to latitude and time of year  Equator = 17 km  Poles = 6-8 km

Stratosphere  Second layer of the atmosphere –Extends from the troposphere to 50 km above the surface  Ozone layer is found here  At the bottom of the layer the temperature is about -60°C –Temperature increases as altitude increases in this layer –Caused by the absorption of solar energy by the ozone layer

Stratosphere  Stratopause: –High temperature zone between the stratosphere and next layer; upper boundary of stratosphere –Highest temperature is around 0°C - freezing

Mesosphere  Layer that extends from the stratosphere to 80 km above the surface  Temperature decreases as the altitude increases –Coldest layer in the atmosphere –Drops to -90°C  Mesopause: –Upper boundary of mesosphere –temperature begins to increase

Thermosphere  Layer above the mesopause  Temperature increases steadily with altitude –Nitrogen and oxygen atoms absorb solar energy  Very thin layer –Thermometer can not accurately measure temperature –Special instruments are needed to determine the temperature  Temperatures of more than 2000°C have been recorded

Thermosphere  To figure out temperature –Scientists find density  Determined by how much drag is on satellites –Use density to find temperature  Ionosphere: –Around 80 km to 550 km –Solar rays are absorbed and cause gas molecules to lose electrons  Creates ions  Ion can reflect radio waves back to earth  Changes altitude depending on time of day

Thermosphere  Exosphere: –Extends for thousands of km –Where the earth’s atmosphere blends into space