Chapter 4 outline: weather

APES notes atmosphere, weather

see also frog book 15.1 (atmosphere) and 6.1 (biomes)

Three ways heat energy moves:

• Radiation: no medium needed, e.g. light
  
• Conduction: contact
  
• Convection: matter in motion

Summary:

• Solar radiation passes through the atmosphere
  
• Radiation hits the earth surface, conducts to air
  
• Hot air rises, (convection) cooler air comes in to take its place
  
• This is the basis for wind (air along the surface) and weather (condensation and precipitation)
  

--------------n.b. (nota bene, "note well")--------------

• Tilt of the earth: Basis for seasons : tilt away=winter
  
• equinox=equal night, solstice=extremes
  
• Equator is hottest, so greatest convection there, also ocean less salty there (why?)
  

Three global convective cells, cause winds, climates and all weather:

Hadley, Ferrel, Polar

• Ocean currents follow the winds, clockwise in N hemisphere
  
• Cells converge at rainy spots, diverge at deserts
  
• Why? Clouds lift at convection spots, cooling them = rain
  
• Dry air dropping from space = warm, dry air (deserts)
  

Layers: spheres bottom to top

• tropo: at the surface, where all weather happens, conduction to air from surface, convection to other layers, albedo is how much energy it reflects (albus=white)
  
• strato: higher, drier air, cooler, air travel is here, also ozone layer (stops UV)
  
• meso: middle
  
• thermo: hot, charged particles, also ionosphere, bounces radio waves
  
• exo: outer
  
• magneto; even further, deflects solar wind, protects surface (none on Mars)
  

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Air stuff:

• compress air and it heats (bicycle pump)
  
• uncompress air (e.g. altitude) it cools (spray can too)
  
• warmer air holds more water (more energy to keep molecules in gas phase)
  
• cooler air holds less water
  
• humidity measures how much water in how much air
  
• relative humidity: compared to how much it can hold at that temp
  
• absolute humidity: total amount of water
  
• dew point: temp where water condenses
  
• rising air condenses (rain) “adiabatic cooling” rain carries the heat away
  
• falling air heats (e.g deserts) “adiabatic heating” absorbs energy from the surroundings
  
• rain shadows=dry areas after mountains 
  
• moon shadow=a cool song by Cat Stevens
• saturated 100% RH air is fog, then rain or snow

Cells:

ITCZ: at the equator, inter-tropical-convergence-zone

Hadley cell: equator to 30°N or 30°S

Ferrel cell: 30-60°

Polar cell: 60-90°

• since earth is spinning, as air flows south, it also falls a bit west=tradewinds
  
• if air flows north, it also flows a bit east=westerlies (weather describes wind from source direction)
  
• this change of direction creates the coriolis effect
  
• Hurricanes are low pressure systems, rising air creates a counter-clockwise flow (L on the weather maps)
  
• High pressure systems create clockwise flow (H on the weather map)
  

Oceans:

• winds carry surface water along, so N hemisphere has clockwise currents (cool water off CA coast)
  
• a special current from Greenland melt flows to Hawaii, called the thermo (heat) haline (salt) current.
  
• ENSO is a big deal: normally winds carry water off-shore of chile, bringing up food from the deep ocean (happy fisherpeeps).
  
• El Niño reverses this, so sad fisherpeeps
  
• La nada is no flow at all