Title: NATS 101 Lecture 2 TR Atmospheric Composition Vertical Structure Weather
1NATS 101Lecture 2 TRAtmospheric
CompositionVertical Structure Weather
Climate
2Atmospheric CompositionPermanent Gases
- N2 and O2 are most abundant gases
- Percentages hold constant up to 80 km
- Ar, Ne, He, and Xe are chemically inert
- N2 and O2 are chemically active, removed
returned
Ahrens, Table 1.1, 3rd Ed.
3N2 and O2
N2 Boiling point 77 K or -196C or 320 F
O2 Boiling point 90 K or -183 C or -297 F
Balance between input (production) and output
(destruction)
Input plant/animal decaying Sink soil
bacteria oceanic plankton--gtnutrients
Input plant photosynthesis Sink organic
matter decay chemical combination
(oxidation) breathing
4Atmospheric CompositionImportant Trace Gases
Ahrens, Table 1.1, 3rd ed.
Which of these is now wrong even in the 4th
edition of Ahrens?
5Carbon Dioxide CO2
Sources vegetative decay volcanic
eruptions animal exhalation combustion of fossil
fuels(CH4 2 O2 gt 2 H2O CO2) Sinks photosynth
esis (oxygen production) dissolves in
water phytoplankton absorption (limestone
formation)
6CO2 Trend
Keeling Curve Some gases vary by season and
over many years. The CO2 trend is the cause
for concern about global warming.
CO2 increases in northern spring, decreases in
northern fall
http//earthguide.ucsd.edu/globalchange/keeling_cu
rve/01.html
7H2O Vapor VariabilityPrecipitable Water (mm)
Some gases can vary spatially and daily
8Aerosols
- 1 cm3 of air can contain as many as 200,000
- non-gaseous particles.
- dust
- dirt (soil)
- salt from ocean spray
- volcanic ash
- water
- pollen
- pollutants
9Aerosols - Volcanic Ash
Fig. 1-4, p.6
10Aerosols - Dust Particles
Dust Storm on Interstate 10, between Phoenix and
Tucson, AZ.
11Aerosols
- Provide surfaces upon which water vapor can
condense. - Provide a surface area or catalyst needed for
much atmospheric chemistry. - Aerosols can deplete stratospheric ozone. They
can also cool the planet by reflecting sunlight
back to space.
12Two Important Concepts
- Lets introduce two new concepts...
- Density
- Pressure
13What is Density?
- Density (?) Mass (M) per unit Volume (V)
- ? M/V
- ? Greek letter rho
- Typical Units kg/m3, gm/cm3
- Mass
- molecules ? molecular weight (gm/mole)
- Avogadro number (6.023x1023 molecules/mole)
14Density Change
- Density (?) changes by altering either
- a) molecules in a constant volume
- b) volume occupied by the same molecules
a
b
15What is Pressure?
- Pressure (p) Force (F) per unit Area (A)
- Typical Units pounds per square inch (psi),
millibars (mb), inches Hg - Average pressure at sea-level
- 14.7 psi
- 1013 mb
- 29.92 in. Hg
16Pressure
- Can be thought of as weight of air above you.
- (Note that pressure acts in all directions!)
- So as elevation increases, pressure decreases.
Higher elevation Less air above Lower
pressure Lower elevation More air above Higher
pressure
Top
Bottom
17Density and Pressure Variation
- Key Points
- Both decrease rapidly with height
- Air is compressible, i.e. its density varies
Ahrens, Fig. 1.5
18Why rapid change with height?
- Consider a spring with 10 kg bricks on top of it
- The spring compresses a little more with each
addition of a brick. The spring is compressible.
19Why rapid change with height?
- Now consider several 10 kg springs piled on top
of each other. - Topmost spring compresses the least!
- Bottom spring compresses the most!
- The total mass above you decreases rapidly
w/height.
? mass
? mass
? mass
? mass
20Why rapid change with height?
- Finally, consider piled-up parcels of air, each
with the same molecules. - The bottom parcel is squished the most.
- Its density is the highest.
- Density decreases most rapidly at bottom.
21Why rapid change with height?
- Each parcel has the same mass (i.e. same number
of molecules), so the height of a parcel
represents the same change in pressure ?p. - Thus, pressure must decrease most rapidly near
the bottom.
?p
?p
?p
?p
22Water versus Air
- Pressure variation in water acts more like
bricks, close to incompressible, instead of like
springs.
Air Lower density, Gradual drop Higher
density Rapid decrease
Top
Top
Water Constant drop Constant drop
Bottom
Bottom
23A Thinning Atmosphere
Lower density, Gradual drop w/elevation High
er density, Rapid decrease w/elevation
NASA photo gallery
24Pressure Decreases Exponentially with Height
- Logarithmic Decrease
- For each 16 km increase in altitude, pressure
drops by factor of 10. - 48 km - 1 mb 32 km - 10 mb 16 km - 100
mb 0 km - 1000 mb
1 mb
48 km
10 mb
32 km
100 mb
16 km
Ahrens, Fig. 1.5
25Exponential Variation
- Logarithmic Decrease
- For each 5.5 km height increase, pressure drops
by factor of 2. - 16.5 km - 125 mb 11 km - 250 mb 5.5 km - 500
mb 0 km - 1000 mb
26Equation for Pressure Variation
- We can Quantify Pressure Change with Height
27What is Pressure at 2.8 km?(Summit of Mt. Lemmon)
- Use Equation for Pressure Change
28What is Pressure at Tucson?
- Use Equation for Pressure Change
- Lets get cocky
- How about Denver? Z1,600 m
- How about Mt. Everest? Z8,700 m
- You try these examples at home for practice
29Temperature (T) Profile
- More complex than pressure or density
- Layers based on the Environmental Lapse Rate
(ELR), the rate at which temperature decreases
with height.
Ahrens, Fig. 1.7
30Higher Atmosphere
- Molecular Composition
- Homosphere- gases are well mixed. Below 80 km.
Emphasis of Course. - Heterosphere- gases separate by molecular weight,
with heaviest near bottom. Lighter gases (H, He)
escape.
Ahrens, Fig. 1.8
31Atmospheric Layers Essentials
- Thermosphere-above 85 km
- Temps warm w/height
- Gases settle by molecular weight (Heterosphere)
- Mesosphere-50 to 85 km
- Temps cool w/height
- Stratosphere-10 to 50 km
- Temps warm w/height, very dry
- Troposphere-0 to 10 km (to the nearest 5 km)
- Temps cool with height
- Contains all H2O vapor, weather of public
interest
32Summary
- Many gases make up air
- N2 and O2 account for 99
- Trace gases CO2, H2O, O3, etc.
- Some are very importantmore later
- Pressure and Density
- Decrease rapidly with height
- Temperature
- Complex vertical structure
33Climate and Weather
- Climate is what you expect.
- Weather is what you get.
- -Robert A. Heinlein
34Weather
- Weather The state of the atmosphere
- for a specific place
- at a particular time
- Weather Elements
- 1) Temperature
- 2) Pressure
- 3) Humidity
- 4) Wind
- 5) Visibility
- 6) Clouds
- 7) Significant Weather
35Surface Station Model
Responsible for boxed parameters
- Temperatures
- Plotted ?F in U.S.
- Sea Level Pressure
- Leading 10 or 9 is not plotted
- Examples
- 1013.8 plotted as 138
- 998.7 plotted as 987
- 1036.0 plotted as 360
Ahrens, p 431
36Sky Cover and Weather Symbols
Ahrens, p 431
Ahrens, p 431
37Pressure Tendency
- Change in pressure over the past 3 hours is also
plotted. - Also called barometric tendency
Ahrens, p 432
38Wind Barbs
- Direction
- Wind is going towards
- Westerly ? from the West
- Speed (accumulated)
- Each flag is 50 knots
- Each full barb is 10 knots
- Each half barb is 5 knots
65 kts from west
Ahrens, p 432
39SLP pressure
temperature dew point
cloud cover
Ohio State website
wind
40Practice Surface Station
- Temperate (oF)
- Pressure (mb) Last Three Digits (tens, ones,
tenths) - Dew Point (later) Moisture
- Wind Barb Direction and Speed
- Cloud Cover Tenths total coverage
41Practice Surface Station
- Sea Level Pressure
- Leading 10 or 9 is not plotted
- Examples
- 1013.8 plotted as 138
- 998.7 plotted as 987
- 1036.0 plotted as 360
42Surface Map Symbols
- Fronts
- Mark the boundary between different air
masseslater -
- Significant weather occurs near fronts
- Current US Map
Ahrens, p 432
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44Radiosonde
- Weather balloons, or radiosondes, sample
atmospheric to 10 mb. - They measure temperature moisture pressure
- They are tracked to get winds
Ahrens, Fig. 1
45Radiosonde Distribution
- Radiosondes released at 0000 and at 1200 GMT for
a global network of stations. - Large gaps in network over oceans and in less
affluent nations. - Stations 400 km apart over North America
46Radiosonde for Tucson
- Example of data taken by weather balloon released
over Tucson - Temperature (red)
- Moisture (green)
- Winds (white)
- Note variations of all fields with height
- UA Tucson 1200 RAOB
stratosphere
tropopause
troposphere
temperature profile
moisture profile
wind profile
47Upper-Air Model
Responsible for boxed parameters
- Conditions at specific pressure level
- Wind
- Temperature (?C)
- Moisture (Later)
- Height above MSL
- UA 500mb Analysis
Ahrens, p 431
Ahrens, p 427
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49Reading Assignment
- Ahrens
- Pages 13-22
- Problems 1.17, 1.18, 1.20
- (1.17 ? Chapter 1, Question 17)
- Pages 25-30
- Problems 2.1-2.4
- (2.1 ? Chapter 2, Problem 1)
- Dont Forget the 4x6 Index Cards