Radiation Heat and Temperature Perihelion Aphelion Great Circle

Radiation, Heat, and Temperature

Perihelion Aphelion

Great Circle Largest possible circle on a sphere Formed by passing a plane through the center of a sphere Great circles bisect sphere (cut it in half) Great circle routes are the closest distance between two points on surface Example: Equator

Any two great circles must bisect each other Blue circle cuts red circle in half (and vice-versa)

Latitude “lines” identify north-south location on a sphere All latitudes are “small circles” except for the equator

LONGITUDE Longitude “lines” (meridians) identify east-west location on a sphere Each longitude is half of a great circle (example: 90°west and 90°east)

CIRCLE OF ILLUMINATION A great circle dividing sunlit and dark hemispheres of Earth (day vs. night) The circle of illumination is not usually oriented along Earth’s polar axis.

TIME DEPENDS ONLY ON LONGITUDE Looking down on North Pole

SEASONS

APPARENT SOLAR PATH AT DIFFERENT LATITUDES Chapter 3, pp. 60– 66

Cross-Quarter Days Oct 31 Aug 1 Feb 2 May 1

Solar Radiation Spectrum

Sun vs. Earth Infrared

Rayleigh Scattering longer waves are not scattered shorter waves are scattered

Rayleigh Scattering

Rayleigh Scattering Cyan sky is mix of visible intensities coupled with eye sensitivity

Rayleigh Scattering

Setting sun appears red because shorter visible wavelengths (blue through yellow/orange) are scattered

Mie Scattering all wavelengths are scattered

Mie Scattering

20. 1 (Mie)

Low sun = low transmissivity (longer path of radiation through atmosphere)

Solar Constant Solar “constant” decreases with increasing distance from sun

Clouds and Solar Radiation

Net Radiation by Latitude

AVERAGE JANUARY TEMPERATURE (°F)

AVERAGE JULY TEMPERATURE (°F)