Chapter 2 Solar Heating

(Variations in) Solar Heating Power Weather Important Global and Seasonal Variations: Low latitudes receive more solar heating than high latitudes Amount of solar heating varies by season, especially at higher latitudes Solar Heating: electromagnetic radiation (mainly light) from the Sun warms the Earth’s surface (which heats the troposphere).

Electromagnetic Radiation

Solar heating is greater at low latitudes than high latitudes Less incident radiation per unit area (i.e., heat/m 2 ) at high latitudes Also, more reflection (on average) at high latitudes (angle, ice), radiation passes thru more air

Sun at 90 o Maximum heating Sun at 45 o Heating cut by 1/3 Sun at 30 o Heating cut by 1/2 Low Sun Angle Causes Less Heating

Earth-Sun Relations

Earth’s Inclined Spin Axis and Orbit Around the Sun Creates the Seasons

Length of Daylight Summer Solstice Winter Solstice Spring/Fall Equinox

Summer Solstice: High sun angle, long days (15 hours in Orem) Sun rises and sets to north of due east & west respectively At 40 o N latitude (Orem)

Fall and Spring Equinoxes : Medium sun angle, 12 hour days Sun rises due east, sets due west At 40 o N latitude (Orem)

Winter Solstice: Low sun angle, short days (9 hrs 15 min in Orem) Sun rises and sets well south of due east & west, respectively At 40 o N latitude (Orem)

View due west along 17 th South, Spring Equinox sunset, SLC

Note the shadow. Near the Tropic of Cancer just before the Summer Solstice the sun is nearly straight overhead.

Why don’t the tropics get hotter and hotter,while the poles cool? page 167 On average, more heat enters Earth-atmosphere system than leaves at low latitudes and vice versa at high latitudes

Interactions of Sunlight with the Atmosphere and Solid Earth Scattering Reflection Absorption Re-radiation

Reflection Energy in the light is lost back to space Air, clouds, ground reflect light Albedo is the percentage of light that a substance reflects Earth’s albedo ~ 30% Snow ~ 80-90% Water 5-80% (!) Moon 7%

Scattering Light ray is split into multiple weaker rays that head off in various directions Some energy is lost to space Air tends to scatter blue light; red light is scattered much less

Scattering is Why the Sky is Blue and Sunsets are Red

What Happens to Solar Radiation? 50% absorbed by land & sea 20% absorbed by atmosphere and clouds 30% lost to space by reflection and scattering

Absorption Much Light Energy is Absorbed (by Rocks, Water, Plants) It can be converted to other Forms of Energy: Kinetic Energy (energy of motion, e.g., wind) Potential Energy (e.g., chemical, gravitational; evaporation) Heat Energy (T is raised) Electromagnetic Radiation (ground, etc. re- radiates the energy towards space

The Absorbed Heat Energy Can then Be Transferred Mechanisms of Heat Transfer:

The Earth Emits Infrared Radiation in Response to its Temperature All substances emit radiation in response to their temperature. In general, hotter substances emit shorter wavelength radiation, and more radiation

Greenhouse Effect: The Atmosphere Partially Blocks the escape of the emitted infrared radiation, keeping the Earth warmer. Absorption of visible light and infrared radiation by the atmosphere

The Greenhouse Effect

Reflection and Earth’s Albedo

Chapter 2 END