Ch 2 Solar Energy to Earth and the Seasons Wednesday September 17 2014 4 09 PM Tropic of Cancer 23 5 N Tropic of Capricorn 23 5 S Energy Imbalance Energy flow heat redistribution Earth s climate atmosphere and oceanic circulation The energy flow is imbalanced to redistribute the energy throughout the earth Sinks Sources Seasonality Response to the changes in the sun s altitude angle between the horizon and the sun The sun s altitude at sunrise or sunset If the sun reaches to the point directly overhead the altitude is 90 degrees Where is this possible Subsolar point 90 degrees Zenith Seasonal changes The sun s declination latitude of the subsolar point 23 5 N to 23 5 S Migrates annually between Tropic of Cancer and the Troppic of Capricorn Does the subsolar point reach to the continental U S No We never receive direct sunlight Seasonality Changes in Radiation Day length Number of hours of sunshine varies with latitude There is no variability at the equator Equator has 12 hours of night and day year round Greatest variability is at the poles Why do we have seasons 1 Revolution earth s orbit around the sun Earth travels at 107 000 km h in an elliptical orbit one rev 365 25 days 2 Rotation spin of earth on its own axis counterclockwise eastward Causes daily cycle of daylight and darkness circle of illumination 24 hours per rotation 3 Tilt of Earth s Axis Axis maintains alignment during orbit around the sun 4 Axial Parallelism Axis maintains alignment during orbit around the sun 5 Sphericity surface area covered by a given amount of insolation Annual March of the Seasons March Spring equinox March 21st rays of sun striking the equator all places on earth experience 24 hours of day and night June summer solstice June 21st 24 hours of daylight in the arctic circle north and 24 hours of darkness in Antarctica sun rays striking the Tropic of Cancer September fall equinox Sept 21st rays of sun strike equator 12 hours of day and night everywhere December winter solstice Dec 21st Arctic Circle is 24 hours of darkness Antarctica is 24 hours of daylight sun rays strike the Tropic of Capricorn