NATS 101 Lecture 2 TR Atmospheric Composition Vertical Structure Weather & Climate

Lecture 2-Nats 1012 Atmospheric Composition Permanent Gases N 2 and O 2 are most abundant gases Percentages hold constant up to 80 km Ar, Ne, He, and Xe are chemically inert N 2 and O 2 are chemically active, removed & returned Ahrens, Table 1.1, 3 rd Ed.

Lecture 2-Nats 1013 N 2 Boiling point: 77 °K or -196°C or –320 °F O 2 Boiling point: 90 °K or -183 °C or -297 °F N 2 and O 2 Balance between input (production) and output (destruction): Input: plant/animal decaying Sink: soil bacteria; oceanic plankton-->nutrients Input: plant photosynthesis Sink: organic matter decay chemical combination (oxidation) breathing

Lecture 2-Nats 1014 Atmospheric Composition Important Trace Gases Ahrens, Table 1.1, 3 rd ed. Which of these is now wrong even in the 4th edition of Ahrens?

Lecture 2-Nats 1015 Sources vegetative decay volcanic eruptions animal exhalation combustion of fossil fuels (CH O 2 > 2 H 2 O + CO 2 ) Sinks photosynthesis (oxygen production) dissolves in water phytoplankton absorption (limestone formation) Carbon Dioxide CO 2

Lecture 2-Nats 1016 CO 2 Trend “Keeling Curve” Some gases vary by season and over many years. The CO2 trend is the cause for concern about global warming. CO 2 increases in northern spring, decreases in northern fall

Lecture 2-Nats 1017 H 2 O Vapor Variability Precipitable Water (mm) Some gases can vary spatially and daily

Lecture 2-Nats 1018 Aerosols 1 cm 3 of air can contain as many as 200,000 non-gaseous particles. –dust –dirt (soil) –salt from ocean spray –volcanic ash –water –pollen –pollutants

Lecture 2-Nats 1019 Aerosols - Volcanic Ash Fig. 1-4, p.6

Lecture 2-Nats Aerosols - Dust Particles Dust Storm on Interstate 10, between Phoenix and Tucson, AZ.

Lecture 2-Nats Aerosols 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.

Lecture 2-Nats Two Important Concepts Let’s introduce two new concepts... Density Pressure

Lecture 2-Nats What is Density? Density (  ) = Mass (M) per unit Volume (V)  = M/V  = Greek letter “rho” Typical Units: kg/m 3, gm/cm 3 Mass = # molecules  molecular weight (gm/mole) Avogadro number (6.023x10 23 molecules/mole)

Lecture 2-Nats Density Change Density (  ) changes by altering either a) # molecules in a constant volume b) volume occupied by the same # molecules a b

Lecture 2-Nats What 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 in. Hg

Lecture 2-Nats Pressure 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 Bottom Top

Lecture 2-Nats Density and Pressure Variation Key Points 1.Both decrease rapidly with height 2.Air is compressible, i.e. its density varies Ahrens, Fig. 1.5

Lecture 2-Nats Why rapid change with height? Consider a spring with 10 kg bricks on top of it compressible The spring compresses a little more with each addition of a brick. The spring is compressible. 10 kg

Lecture 2-Nats Why 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

Lecture 2-Nats Why 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.

Lecture 2-Nats Why 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 pppp pppp pppp

Lecture 2-Nats Water 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 Bottom Top Bottom Top Water: Constant drop

Lecture 2-Nats A Thinning Atmosphere Bottom Top Lower density, Gradual drop w/elevation Higher density, Rapid decrease w/elevation NASA photo gallery

Lecture 2-Nats Pressure Decreases Exponentially with Height Logarithmic Decrease For each 16 km increase in altitude, pressure drops by factor of km - 1 mb 32 km - 10 mb 16 km mb 0 km mb 100 mb 10 mb 1 mb 16 km 32 km 48 km Ahrens, Fig. 1.5

Lecture 2-Nats Exponential Variation Logarithmic Decrease For each 5.5 km height increase, pressure drops by factor of km mb 11 km mb 5.5 km mb 0 km mb

Lecture 2-Nats Equation for Pressure Variation We can Quantify Pressure Change with Height

Lecture 2-Nats What is Pressure at 2.8 km? (Summit of Mt. Lemmon) Use Equation for Pressure Change

Lecture 2-Nats What is Pressure at Tucson? Use Equation for Pressure Change Let’s get cocky… How about Denver? Z=1,600 m How about Mt. Everest? Z=8,700 m You try these examples at home for practice

Lecture 2-Nats Temperature (T) Profile More complex than pressure or density Layers based on the Environmental Lapse Rate (ELR), the rate at which temperature decreases with height. inversion isothermal 6.5 o C/km Ahrens, Fig. 1.7

Lecture 2-Nats Higher 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

Lecture 2-Nats Atmospheric 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” H 2 O vapor, weather of public interest

Lecture 2-Nats Summary Many gases make up air N 2 and O 2 account for ~99% Trace gases: CO 2, H 2 O, O 3, etc. Some are very important…more later Pressure and Density Decrease rapidly with height Temperature Complex vertical structure

Lecture 2-Nats Climate and Weather “Climate is what you expect. Weather is what you get.” -Robert A. Heinlein

Lecture 2-Nats Weather 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

Lecture 2-Nats Surface Station Model Temperatures Plotted  F in U.S. Sea Level Pressure Leading 10 or 9 is not plotted Examples: plotted as plotted as plotted as 360 Ahrens, p 431 Responsible for boxed parameters

Lecture 2-Nats Sky Cover and Weather Symbols Ahrens, p 431

Lecture 2-Nats Pressure Tendency Change in pressure over the past 3 hours is also plotted. Also called barometric tendency Ahrens, p 432

Lecture 2-Nats Wind Barbs Direction Wind is going towards Westerly Westerly  from the West Speed (accumulated) Each flag is 50 knots Each full barb is 10 knots Each half barb is 5 knots Ahrens, p kts from west

Lecture 2-Nats temperature dew point SLP pressure wind cloud cover Ohio State website

Lecture 2-Nats Practice Surface Station Temperate ( o F) Pressure (mb) Last Three Digits (tens, ones, tenths) Dew Point (later) Moisture Wind Barb Direction and Speed Cloud Cover Tenths total coverage Ahrens, p Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction?

Lecture 2-Nats Practice Surface Station Sea Level Pressure Leading 10 or 9 is not plotted Examples: plotted as plotted as plotted as 360 Ahrens, p Decimal point What are Temp, Dew Point, SLP, Cloud Cover, Wind Speed and Direction?

Lecture 2-Nats Surface Map Symbols Fronts Mark the boundary between different air masses…later Significant weather occurs near fronts Current US Map Ahrens, p 432

Lecture 2-Nats 10143

Lecture 2-Nats Radiosonde Weather balloons, or radiosondes, sample atmospheric to 10 mb. They measure temperature moisture pressure They are tracked to get winds Ahrens, Fig. 1

Lecture 2-Nats Radiosonde 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

Lecture 2-Nats Radiosonde 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 troposphere stratosphere tropopause temperature profile moisture profile wind profile

Lecture 2-Nats Upper-Air Model Conditions at specific pressure level Wind Temperature (  C) Moisture (Later) Height above MSL UA 500mb Analysis Ahrens, p 427 Ahrens, p 431 Responsible for boxed parameters

Lecture 2-Nats 10148

Lecture 2-Nats Reading Assignment Ahrens Pages Problems 1.17, 1.18, 1.20 (1.17  Chapter 1, Question 17) Pages Problems (2.1  Chapter 2, Problem 1) Don’t Forget the 4”x6” Index Cards