NATS 101 Lecture 2 Vertical Structure of the Atmosphere

Vertical Structure of the atmosphere 1.Pressure 2.Density 3.Temperature

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 Pressure:

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

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

Equation for Pressure Variation We can Quantify Pressure Change with Height

What is Pressure at 2.8 km? (Summit of Mt. Lemmon) Use Equation for Pressure Change: p (at elevation Z in km) = p MSL x 10 -Z/(16 km) Set Z = 2.8 km, p MSL = 1013 mb p (2.8 km) = (1013 mb) x 10 –(2.8 km)/(16 km) p (2.8 km) = (1013 mb) x 10 –(0.175) p (2.8 km) = (1013 mb) x = 677 mb

What is Pressure at Tucson? 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 Use Equation for Pressure Change: p (at elevation Z in km) = p MSL x 10 -Z/(16 km) Set Z = 800 m, p MSL = 1013 mb

______ Density:  = (kg/m 3 or g/cm 3 ) mass volume Initial State      Incompressible fluid Initial State      Compressible fluid The density of the gases that make up the atmosphere is constantly changing. In addition, the atmosphere is compressible.

Sea-level Near sea level, air density ~ 1.2 kg m -3. Denver, CO At Denver CO, (~1.6 km altitude – or 1 mile), air density is approximately 85% of that at sea level, or 1.01 kg m –3.

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

“Standard atmosphere” is calculated based on profiles at 30  latitude. Temperature Stratification Divide into several vertical layers based on electrical, temperature, and chemical (homogeneous/heterogeneous), characteristics. Together with the change in density with height, this gives the atmosphere its structure.

Troposphere Majority of the weather occurs here The lapse rate is the average decrease in temperature with height ~ 6.5°C/km Contains 80% of the atmospheric mass Tropopause Depth ranges from ~8 km at the poles to ~16 km in the tropics Rapid decrease in temperature with height Layer of most interest to this course!!!

Little weather occurs here Isothermal in lowest 10 km Lapse rate is 0 Contains ~19.9% of the atmospheric mass Stratopause Temperature increases with height from 20-~50 km (Temperature inversion) Ozone layer The ozone layer absorbs much of the incoming solar radiation, warming the stratosphere, and protecting us from harmful UV radiation Layer of some interest to this course!!! Stratosphere

Temperature once again decreases with height Mesosphere Temperature once again increases with height Thermosphere Neither of these layers have much interest for the Meteorologist

Ionosphere - extends from the upper mesosphere into the thermosphere. Contains large numbers of charged particles called ions. Ions are atoms or molecules that have gained an electron or lost an electron so that they carry a charge. This occurs in the upper atmosphere because the molecules are being constantly bombarded by solar radiation. Important for reflecting AM radio waves back to Earth. Also responsible for the aurora borealis (northern lights) and aurora australis (southern lights).

Divide the atmosphere into several vertical layers based on temperature characteristics. Together with the change in density with height, this gives the atmosphere its structure. Troposphere Stratosphere Mesosphere Thermosphere Summary: Temperature Inversion Stable layer

Temperature inversion tropopause T-profile