Lab 2 – September 11, 2013More on Radiation, The Four Seasons, Solstice and Equinox, Sun Angle and the Surface, Seasonality

Radiation Review Everything emits radiation (T>0 Kelvin) Stefan-Boltzmann Law:

E = σT4

Stefan-Boltzmann Constant σ = 0.0000000567 W/(m2K4)

Energy Emitted ∝ Temperature (to the fourth power)

Where is the greatest radiationmeasurement? The least?

Note: Temp of Clouds < Temp of Surface

Downwelling Radiation Downward emission of infrared energy (in our case, from

clouds) Results in higher surface temperatures e.g. Cloudy nights are typically warmer than clear nights

Intensity of downwelling radiationIncreased surface temperatures

Incoming Solar Radiation and the Atmosphere

Some solar radiation traveling through the atmosphere is back-scattered

Solar radiation striking the earth at an angle travels through more atmosphere

Clouds in the atmosphere back-scattera lot of incoming sunlightWhich person experiences more intense sunlight?

The Four SeasonsEarth’s axis always points in the

same direction in space

Time-lapse photography showing concentric, circular star trails

What astronomical feature is in the center?

The Four SeasonsVariations in seasonal

temperatures is a result of the Earth’s tilt

Sun Directly over-head at 23.5° S

Sun Directly over-head at 0°

Sun Directly over-head at 0°

Sun Directly over-head at 23.5° N

Solstice and Equinox (Northern Hemisphere)

Date Latitude of Direct Sunlight

Summer Solstice June 21 23.5° N (Tropic of Cancer)

Winter Solstice December 21 or 22 23.5° S (Tropic of Capricorn)

Autumnal Equinox September 22 0° (Equator)

Vernal (Spring) Equinox

March 20 0° (Equator)

Note: Solstices are reversed for Southern Hemisphere

Sun Angle and the SurfaceThe greater the sun angle, the

more concentrated the radiation is when it strikes the surface

SeasonalityAnnual range of temperature at a

locationi.e. swings in temperature

between summer and winterMajor controllers in seasonality:

◦Latitude◦Proximity to large bodies of water

Seasonality (Latitude)Higher latitudes receive widely varying

solar radiation throughout the yearThink about hours of daylight in each

season◦North Pole?◦Equator?

Seasonality (Bodies of Water)Heat Capacity – a measure of the ratio of the

amount of energy absorbed (or released) by a substance to the corresponding temperature increase (or decrease)

If it requires 40 units of energy to increase the temperature of one gram of dirt by one Kelvin and requires 120 units of energy to increase the temperature of one gram of water one Kelvin, which substance has a higher heat capacity?

H.C. Water > H.C. Land

Seasonality (Bodies of Water)

Seasonality (Bodies of Water)

Lab 2 Problems2.7a,b2.10a,b2.11a,b2.13a,c,d3.13.43.63.9a,b,c

DUE FRIDAY BEFORE CLASS