Chapter 1
The Earth’s Atmosphere
Breaking Down The Atmosphere
- There are lots of different ways to break down or classify the atmosphere
- Let’s start with the gaseous composition
Gaseous Composition
- Break down by permanent gas content
Gas
|
Symbol
|
Percent
|
Nitrogen
|
N2
|
78.08
|
Oxygen
|
O2
|
20.95
|
Argon
|
Ar
|
.93
|
Neon
|
Ne
|
.0018
|
Helium
|
He
|
.0005
|
Hydrogen
|
H2
|
.00006
|
Xenon
|
Xe
|
.000009
|
Break down by variable gas content
Gas/Particles
|
Symbol
|
Percent
|
PPM
|
Water Vapor
|
H2O
|
0 to 4
|
|
Carbon Dioxide
|
CO2
|
.037
|
374
|
Methane
|
CH4
|
.00017
|
1.7
|
Nitrous Oxide
|
N2O
|
.00003
|
.3
|
Ozone
|
O3
|
.000004
|
.04
|
Particulates
|
|
.000001
|
.01 – .15
|
Chlorofluorocarbons
|
|
.00000002
|
.0002
|
- Note Ozone ppm is higher in the stratosphere (5-12 ppm)
Greenhouse Gases
- The most abundant greenhouse gas is water vapor at 4% or less
- It is considered a greenhouse gas because it traps heat
- Consider what happens to temp when it is cloudy
- Other greenhouse gases are Carbon Dioxide, Methane, Nitrous Oxide, and Chlorofluorocarbons
Vertical Structure by Temp.
- The atmosphere reflects 55% of the sun’s energy, so only about 45% gets to earth
- So one way to break down the atmosphere is by temperature
- There are 5 layers:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
- The half-way point of the atmosphere is at 18,000 feet or 3.5 miles
TROPOSPHERE
- Starts at the surface and goes up to an average of 7 miles high (36,000 feet)
- 20,000 ft at the poles to 65,000 at the equator
- It is higher in the summer than winter
- Lapse rate is 2 C/1000 or 3.5 f/1000
TROPOPAUSE
- Boundary layer between troposphere and stratosphere
- Signaled by an abrupt change in the temp lapse rate
- Isothermal air temp remains constant -57º C
- This creates an inversion which keeps most wx below
- The jet stream exists in occasional breaks in the tropopause.
STRATOSPHERE
- Starts at about 39,000 ft
- Temp doesn’t change much creating an inversion
- This inversion keeps the Troposphere’s upward currents down
- High amounts of ozone absorb the sun’s ultraviolet radiation and gives off heat
- At 66,000 temps starts to rise because of the ozone absorbing energy
STRATOPAUSE
- This is the boundary layer between the Stratosphere and the Mesosphere
- It exists at about 164,000 ft
MESOSPHERE
- This one gets colder the further out
- It exists at about 280,000 ft (31 to 53 miles high)
- 99% of the atmosphere exists below this layer
- There is little ozone up here therefore temps decrease with an increase in altitude.
- Lowest average temp found at about 53 miles at -90º C or -130º F
THERMOSPHERE
- This one gets warmer with an increase in altitude.
- 53 to 310 miles
- Radiation excites the oxygen molecule causing a temp increase.
EXOSPHERE
- 310 miles and further
- Consists of atoms and molecules in loose orbit sometimes shooting off into space.
Atmosphere based on Gas
- Homosphere
- composition is fairly uniform
- surface to 53 miles
- Heterosphere
- 53 miles and up
- heavy atoms and molecules settle
Other Regions
- Ionosphere
- not really a layer
- electrified region of the atmosphere
- 37 miles is roughly the bottom
- 180 miles is the greatest concentration
- caused by the sun ionizing the atmosphere
Other Regions
- Magnetosphere
- Solar wind pushes it into the atmosphere
- Increasing ionization making radio communication difficult
- http://www.swpc.noaa.gov/
Aurora Borealis
- 124 to 600 miles out
- Atomic oxygen = green & red
- Atomic nitrogen = red & violet
The Standard Atmosphere
Chapter 2
Heat and Temperature
Temperature
- Temperature is the degree of hotness or coldness of a body or environment.
- Measurement of the energy of the molecules (movement)
- The faster the average speed of the molecular movement, the higher the temperature.
- However, when might it be a 1000ºC and yet be very cold at the same time?
1000 Degrees and Freezing to Death
- In order for our skin to detect a change in temp we must experience an extremely high number of molecules colliding into it.
- At high altitudes, such as those in the Thermosphere, the temperature may be very “hot” (exceeding 1000ºC), but there aren’t enough molecules to warm the skin through conduction.
- Molecules move an average of 1km before bumping into each other in the Thermosphere
Temp vs Heat
- Heat is the total amount of kinetic energy of the atoms and molecules composing a substance
- Since it is energy it can do work
- Heat is measured using a calorimeter
- Heat is measured in Joules
- Temperature is the average kinetic energy
- Temperature is measured with a thermometer
- Temperature is measured in degrees
- Heat flows from hot to cold
Temperature Scales
- (Fº -32) then multiply by 5/9 =˚C
- 5/9 is .55555556
- (Cº * 9/5) then add 32 = Fº
- 9/5 is 1.8
Heat Transfer Mechanisms
- Radiation – Transfer of energy directly to the molecule from an outside source such as the sun.
- Conduction – When one molecule bumps into another giving it some energy
- Convection – Transfer of heat by mass movement of a fluid, like air currents or water currents (a thermal is a good example)
Specific heat
- The measure of heat energy required to raise a substance to a new temperature
- Different substances will warm at different rates when exposed to the same amount of heat energy
- A substance with a low specific heat number warms more than one with a high number
- Notice that water is going to change temp the slowest
Primary Cause of all Wx
- Insolation is when the suns rays warm the earth
- Different surfaces radiate and receive at different rates
- Terrestrial radiation is when the earth radiates the energy back into the atmosphere
- This is referred to as longwave radiation
- The sun’s energy is referred to as shortwave radiation
- Diurnal Variation is difference between day and night (coldest temp just after sunrise)
Controls of Temperature
- Latitude
- Land and water distribution
- Ocean currents
- Elevation
Daily Range of Temp
- The daily range of temp is experienced closest to the ground.
- The higher we go in altitude the less the change in temp
- This takes place because the effects of terrestrial radiation are lessened
- Likewise, areas close to large bodies of water experience less daily temp change
Ocean Currents
The largest daily temp range:
- Browning Montana, January 23, 1916
- Temp went from 44˚F to -56˚F in a 24 hour period
- That is a temp change of 100˚F
Temperature and altitude
- The lapse rate is a measure of the rate of change in temperature with an increase in altitude
- Standard average lapse rate is 2°/1000
- Dry adiabatic lapse rate is about 3°/1000
- The only way to be sure is to take an atmospheric sounding
- Gotten usually by using a radiosonde
- Isothermal layer is a layer where the temperature remains constant with an increase in altitude
- If the temperature increases with altitude it’s an inversion
Inversion
- Increase in temp with an increase in altitude
- Can occur at any altitude in troposphere
- Most common occurrence is on calm clear cool night in which the ground cools air close to it.
- This is caused by terrestrial radiation and is referred to as a Radiation Inversion
Inversion
- This time of year the basin gets one
- Cold stable air near the surface
- Warm overriding air above
- Smooth air
- Poor visibility under the inversion
- The most common inversion occurs near the ground on calm, clear, cool nights
Primary Cause of all Wx
- Seasonal variation – summer to winter
- Length of days and nights
- Latitude variation – angle which the suns rays strike the earth
- Topography variation – arid land Vs vegetation (wet / dry)
- Ocean currents – The Gulf Stream
What causes a L or H pressure? 1
- Temperature
- In a closed container more temp = more pressure
- You might think that the higher the temp the higher the pressure
- But No!
What causes a L or H pressure? 1
- Usually the highest pressures are found in cold regions
- Why?
- Because of Density
- Usually the higher density offsets the lack of movement of the molecules
Density vs Pressure
- Density = mass/volume
- That is, the number of molecules in a given volume
- Pressure = force/area
- 14.7psi at sea level
- That is the tiny push (force) the molecules makes when it bounces off something
- More to come on this topic later
Pressure vs Density
- As you can see most of the pressure and density is close to the surface
- As we go higher the rate of decrease is less severe
What causes a L or H pressure? 2
- Convergence
- movement of air aloft is not always at the same speed
- where it slows down it piles up into a H pressure
- the piling up of air is called convergence
What causes a L or H pressure? 3
- Divergence
- opposite of convergence
- the upper level wind speeds up and stretches the air out creating a L pressure
- usually good wx under an upper level divergence
What causes a L or H pressure? 4
- Thermal tides
- At an average altitude of 60 mi (thermosphere) changes of over 500ºC
- the rapid warming and cooling of upper air causes great density oscillations
- shows up as small pressure changes at the surface because of the high altitude
Quizzes
- Quiz on chapter 1 and 2
- Quiz on the 50 states