The Earth’s Atmosphere and Temperature 1&2

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BBCC Aviation Meteorology

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

  • Table 1-2 in the book

 

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

 

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