Warming Earth and its Atmosphere The Diurnal and Seasonal Cycles

Warming Earth and its Atmosphere The Diurnal and Seasonal Cycles

Or, what happens to the energy received from the sun?

First We Need to Understand The Ways in Which Heat Can be Transferred in the Atmosphere Latent heat Conduction Convection Advection Radiation

1. Convection Heat transfer in the vertical through buoyant motion

Buoyancy When something is less dense than the fluid (gas) that it displaces, it will rise. (and visa versa)

Atmospheric convection Cumulus Cloud Upward Heat Transfer

Evidence of Buoyant Motion in the Atmosphere Hot air balloon, helium balloon, blimp Birds soaring in circles, without flapping their wings Sail planes Shimmering of air over roads and parking lots in summer Cumulus clouds Smoke rising over fire

2. Latent heat the concept

Personal Experiences Latent Heat Consumption by Evaporation Chill stepping out of a shower evaporation consumes heat Use of swamp coolers instead of air conditioners in dry climates It is cooler over green grass than over a stone surface evaporation from leaves Cool breeze with thunderstorms in vicinity evaporation of rain below the cloud

Personal Experiences Latent Heat Release by Condensation or Freezing Spraying fruit trees with water when frost damage is possible freezing of water releases heat The bubbly appearance of cumulus clouds released latent heat in cloud makes them buoyant

Bubbly Cumulus Clouds

The Transport of Latent Heat Condensation Water Vapor ***** ***** Air Moves Vapor to Cloud Droplets Evaporation Heat Taken From Ocean Heat Released In Cloud

3. Conduction Transfer of heat from molecule to molecule Think of heat in terms of how fast the molecules are moving Fast moving molecules where something is hot collide with adjacent slow moving molecules where it is cooler, causing the slower molecules to speed (heat) up.

Heat conductivity ability of material to conduct heat Air -.02 (Watts per meter per o C) Wood -.08 Water -.60 Wet soil - 2.1 Stone - 2.7 Iron - 80.

Thus, Air is a Poor Conductor of Heat (ever think about why thermopane windows work?)

4. Advection Warm air Wind direction X Cold air YOU ARE HERE (Temperature will increase)

5. Radiation Has nothing to do with nuclear radiation this is called electromagnetic radiation Different names are used for different wavelengths of electromagnetic radiation.

Everything with a Temperature above absolute zero emits EMR

Millimeters and Micrometers Measure of length used to express length of short waves Millimeter = one-thousandth of a meter = mm Micrometer = one-millionth of a meter = µm = micron

Intensity of Light Versus Wavelength (µm) Temperature of the sun = 6000 K (10,500 F)

Comments Wavelengths with the greatest intensity are the visible ones. Some of the ultraviolet and infrared wavelengths are also intense.

The Sun s Emission Spectrum Versus Earth s

Q: Is the Atmosphere Transparent to this Radiation? That is, is the Atmosphere Like a Clear Window is to Visible Light?

A: Not Exactly Clear - Sort of Like of a Selectively Dirty Window

What Interferes with Transmission of Light Through the Atmosphere? Some gases called optically active gases. Different gases absorb different wavelengths Particles of dust natural and man-made made Clouds and fog

Absorption by Ozone and Water Vapor Percent Absorbed UV VIZ SUN IR Earth IR SUN UV VIZ IR Earth IR

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SUN UV VIS IR Earth IR Atm Window Percent Absorbed

Now That We Know How Heat is Transferred in the Atmosphere! ---------------------- Putting it All Together

The Atmospheric Energy Checkbook Balance Gains and Losses (On the Average)

Putting the Balance Under a Microscope

How the Warm Ground Heats the Air In Contact With It Convection Ground Conduction in lowest millimeter

The Diurnal and Seasonal Cycles of Heating Exist Because of the Earth- Sun Geometry

The Cycles Diurnal Rotation of Earth on axis every 24 h Annual or seasonal Revolution of Earth around the sun every 365.25 days

Equinoxes: Points in Earth s orbit around the sun where the sun is directly over the equator (12 hrs light & 12 hrs of darkness). Solstice: Points in orbit where the sun is displaced farthest N or S.

Important Latitude Bands o Earth Equator: central latitude Tropics : (23.5 N&S) Latitudes of maximum displacement of the sun Tropic of Cancer: 23.5 N (Summer N. Hem.) Tropic of Capricorn: 23.5 S (Summer S. Hem.) Arctic/Antarctic Circles: 66.5 N&S Latitudes where there is 24 hrs of daylight(nighttime) at summer(winter) solstices

Another Look.

Tropic of Capricorn 23.5 S Arctic circle 66.5 N Tropic of Cancer 23.5 N Equator 0

Seasonal Cycle -Causes- The sun heats the ground less intensely when it is at a low angle in the sky (winter), and more intensely when it is at a high angle above the horizon. The suns heat the ground more when the daylight is longer (Summer).

Average January Temperature Near Sea Level

Average July Air Temperature Near Sea Level

Something Peculiar So why isn t it (on a global average) hotter in January? Southern Hemisphere 81% ocean Northern Hemisphere 61% ocean

Daily Temperature Cycle Balance of Incoming Solar and Outgoing Infrared

Max

Temperature Profile Near The Ground DAY profile Note: Temperatures almost always decrease with height

NIGHT FROST Radiation Inversion: Temperatures increase with height

What Can Effect The Day- Night Temperature Change? Cloud cover reduces diurnal variability Terrain: surface type, mountains, canyons, Wind: causes turbulent mixing of the atmosphere which reduces diurnal variability Approaching weather systems: cold fronts, warm fronts, squall lines, hurricanes Humidity

Topographic Effects on Nighttime Temperature Cold air pooling

Factors That Cause Temperature Variation From Place to Place Latitude warmer to south Land and water distribution winter warmer near water summer cooler near water Ocean currents Warm currents generally on east side of continents, cold currents on the west side Elevation of the surface above sea level Temperature decreases with elevation

Surface type e.g., urban versus rural Surface wetness

Cooler of Higher Elev. Warmer Over Ocean in Winter Warmer to South - More Radiation

Two cities with the same mean annual temperature but with very different climates