The Atmosphere

Earth radius 6,370 km (3,981 miles)The atmosphere extends upward to 500 km (321 miles),HOWEVER, 99% of all atmosphere gasses are below 32 km (20 miles)

ThereforeAlthough the entire atmosphere = 8% of earth’s solid radius 99% of gasses 0.005 = 0.5% (one half of one percent) of earth’s radius

The atmosphere is very thin

Troposphere

Tropopause barrier!

Cloud charts, radiosonde. instruments

Dry Air

Two common gasses, N2 (78%) and O2 (21%), make up 99% of dry air. Other gasses, e.g. CO2 CH4 NO2 and water vapor H2O also play an important role by keeping the atmosphere warm, the “greenhouse effect”.

For Wet Air add water vapor (up to 7% in moist hot tropics)4% is more typical around here.

Solar Heating• The equator receives 2.5 times more sunlight

(insolation [photons / m2 ]), incoming solar radiation, than the poles.

• Highest average annual ocean surface temperatures (~27oC) at equator

• Lowest 0oC at high latitudes• Diff. drives density/pressureDifferences => wind DEMO flashlight and globe

23.5

Density falls off with altitude; pressure is caused by impacts, dense air has more impacts

P = RT

Pressure differences cause WIND

Winds flowing into low pressure = low density areas are said to Flow in response to the Pressure Gradient Force.

Heat vs. Temperature• Atoms in air are in constant motion, the energy of their

motion is known as kinetic energy. Kinetic energy increases as the speed of atomic motion increases. Ek = 1/2mv2 (identify symbols)

• Heat energy is the total kinetic energy of all the atoms in a substance. The more atoms present, the greater the heat.

• Temperature represents the average kinetic energy of the atoms in a substance. A few atoms with rapid motion will have a higher temperature than many atoms with slow motion.

1. Atmosphere Layers w/ Pauses 2. Pressure the weight of air above

4. 75% of gassesIn Troposphere

6.5oC/km

equatorpoles

Ozone layer

6. Note change of sign of lapse rate at Tropopause (next slide)5. lapse rate

3. Tropopause higher at equator

Coriolis Effect

Air masses at rest above the equator are moving

much faster than air masses at rest over us in

NJ.Both must rotate once per day, but the equatorial air

goes much further.

Coriolis EffectAir in Northern Hemispheredeflects to the right, reverse in Southern H.

Equatorial Air has faster spin As it moves toward polesit still has it , so it is faster than land below

DEMO: Coriolis Clip

Coriolis Effect: Flowing winds appear to turn due to earth’s rotation

Winds blowing parallel to isobars are called geostrophic windsThis occurs well above the surface where there is no friction

Notice pressure gradient force always from high to low pressure, but Coriolis perpendicular to actual flow direction

Earth’s rotation appears to turn winds flowing along a pressure gradient

The major wind cells

Coriolis “turns” them

If Earth did not rotate, there would be one cell in each hemisphere. Note the formation of Ocean Current Gyres

LOW

HIGH

LOW

Hadley Cell

Ferrel Cell

Polar Cell

Horizontal temperature differencesTemperature effects density and pressure:

500 mb

700 mb

850 mb

Warm Cold Psurface

If you heat something it expands and gets less denseA 500 millibar pressure level is much higher in hot air. Hotter air has lower density and greater volume

1000 mb

P = R’ T so T = P /R’

Polar Jet FormationPolar Jet Formation

Steep gradients of Steep gradients of Pressure cause Pressure cause higher velocity higher velocity geostrophic geostrophic winds.winds.

This is the trigger This is the trigger for jet stream for jet stream flow.flow.

For the Polar Jet, the eddy is in the Ferrel cell on the upper polar side, and so air flows from the west to the east, the “Westerlies”

Since the pressure difference is great at the boundary, the jet is a very fast wind

More polar air is denser, so it wedges under the low density warm air. Rotation causes an eddy to form

Subtropical Deserts +/- 30o latitude

Highs where Hadley/Ferrel Cells descend

Highs where Hadley/Ferrel Cells descend

Water only compound in three states (liquid, gas, solid) on Earth’s surface. Heat energy is transferred through the atmosphere as water changes fromone state to another.

The atmosphere’s heat is absorbed by water in processes such as melting, sublimation, and evaporation.

“ “ These two transfer the most energy, are less common, don’t cause

storms

Evaporation puts moisture (water vapor gas) into the atmosphere and cools the air

Condensation releases heat to air & forms cloud droplets

“water vapor”

Figure 1-4b

Lifting a moist air mass results in condensation, liquid droplets are clouds, coalescence yields precipitation

Orographic LiftingWindward Rain Forest Leeward Rain-Shadow Desert

Rain also on the high Leeward drainage sometimesFlash floods on dry plateau

Ocean-Current Desert

Also Interior and Polar Deserts

•Frontal lifting occurs when two large air masses of contrasting density (temperature, moisture content) meet.

•The boundary between the air masses is termed a front and may be 10 to 150 km (6-94 miles) across and hundreds of kilometers in length.

Frontal Lifting

http://www.met.tamu.edu/class/Metr304/Dir-surface/surface.html~

cP mT

Friction turns surface winds back toward the pressure gradient.Near the surface, winds almost move from High to Low pressureThey spiral counterclockwise into a Low in Northern Hemisphere

AT THE SURFACE

Buoyancy Lifting

Start Local Heat Hot Air Expands Dense air falls into low density area

hot molecules bounce off the high density floor

bounce up

(heated atomsspeed up

paddle board analogy)

Atoms close together (dense, high pressure) “fall into” the nearly empty (low pressure) area

Figure 1-4a

Define Lapse Rate

Figure 1-3c

Latent Heat of Condensation

Table 1-3

Hurricanes

Hurricanes &Typhoons (Tropical Cyclones)

When extremely hot ocean surface temperatures (>26oC) cause hot, moist surface air, huge clusters of thunderstorms develop at sea. If uplift gets extreme, these can organize into a gigantic Low with spiral storm lines, and winds exceeding 74 mph, a Tropical Cyclone, aka Hurricane

Hurricanes are fueled by Latent Heat of Condensation release.One day equals the energy production of US for a year

Jeanne

Hurricanes need hot Hurricanes need hot moist air as fuel. This is moist air as fuel. This is why they weaken over why they weaken over

landland

Storm Surge

Trapped in House, swept away

Storm Surge

Freshwater (rain) floods cause most

fatalities