SEASONS, ENERGY FLOW AND THE SUN

Why do seasons change? 2 Time and Seasons Factors that affect season change are tilt of axis, revolution and rotation. The reason that the seasons change on Earth is because the tilt of the Earth at 23.5° as it revolves around the Sun. This causes two effects: 1) sunlight strikes the Earth’s surface at different angles during different times of the revolution year. 2) the number of hours of daylight each rotational day varies because the Sun is up for different numbers of hours per day.

Seasons Tilted axis and rotation of Earth combined with revolution around Sun causes the seasons. Tilted axis (23.5 degrees), rotation and revolution cause the northern hemisphere to receive more direct sunlight for more hours than the southern hemisphere during the summer and less direct sunlight for less hours during the winter. So, as one hemisphere is warmer, the other is colder. This condition reverses every 6 months. In other words, this condition is seasonal. The fall and spring represent 3-month transitions from summer to winter and from winter to summer.

Changing Angle of Sunlight Reason for the Seasons 2 Changing Angle of Sunlight The hemisphere tilted toward the Sun receives sunlight at higher angles than the hemisphere tilted away from the Sun. Higher insolation angle means greater intensity of radiant energy (the sun shines more directly on a smaller area).

Why does the equator receive more energy from the Sun throughout the year than Fort Thomas? Since the angle of the Sun at the equator is higher above the horizon than at Fort Thomas, more solar radiation is received at the Equator due to the higher insolation angle. The angle of the Sun above the horizon at Fort Thomas varies from 74 to 27 degrees during the year. The angle of the Sun above the horizon at the equator is never lower than 66.5 degrees during the year.

Identify the Seasons and the Equinox or Solstice, and comment about the number of daylight vs. night hours Season _________ Equinox or Solstice _________ Season _________ Equinox or Solstice Season _________ Equinox or Solstice Season ________ Equinox or Solstice

Identify the Seasons and the Equinox or Solstice Equal day and night—12hr and 12 hr Season _________ Equinox or Solstice spring Less daylight hours, more night hours Less night hours, more daylight hours winter Season _________ Equinox or Solstice summer Season _________ Equinox or Solstice fall Season _________ Equinox or Solstice

The Earth is a Heat Engine Heat engines transfer thermal energy to mechanical energy so that work can be done. A portion of the radiant energy from the Sun is absorbed by the Earth’s surface, causing the internal energy of the substances on the Earth’s surface to increase (both land and water), which increases the average KE of the molecules, which increases the surface temperature. More energy is absorbed at the equator than the poles, which creates a temperature difference, producing atmospheric and hydrospheric (oceanic) heat flow. This heat flow causes movement of matter (transfer of thermal energy to mechanical energy) which then can do work. The flow will occur until the source of radiant energy ceases.

The Result of Differential Heating of the Earth Excess heat builds at the Equator because the angle of insolation is highest in this region. Convection currents move thermal energy from the equator (hot) to the poles (cold). Coriolis effect separates these convection currents into 6 individual belts of prevailing winds. Prevailing winds blowing over the oceans also cause prevailing water currents to develop.

Coriolis Effect breaks up the two hemispheric convection cells into 6 distinct global wind belts http://www.astronomynotes.com/solarsys/coriolisc.gif

Global Wind Belts 1) Polar easterlies 2) Prevailing westerlies The two atmospheric convection cells that move from the equator to the poles are modified by the Coriolis Effect because the Earth rotates. This forms the global wind belts. 1) Polar easterlies 2) Prevailing westerlies 3) Tropical easterlies

Coriolis Effect and Winds -Winds in the northern hemisphere curve clockwise -Winds in the southern hemisphere curve counterclockwise.

Coriolis Effect and Ocean Currents Ocean Currents follow the same pattern as Global winds

Facts About the Sun and Its Energy Composition: Primarily hydrogen and helium Energy Source: Conversion of nuclear potential energy by nuclear fusion of hydrogen into helium at its core to thermal energy Temperature at surface: 5800 K (highest percentage of radiant energy is visible light in yellow-green frequency range) Radiant energy is produced by vibrating charges particles (the hotter the surface, the faster the vibrations and the higher the frequency of radiant energy) Sun produces roughly 6600 W/m2 at its surface Solar Constant: 1360 W/m2 (amount of radiant energy received at top of Earth’s atmosphere)

Potential concentrations of radiant energy as light passes through the atmosphere

From Sun From Earth Visible light range Infrared Light Range The surface of the Sun has a temperature of about 5,800 Kelvin (about 5,500 degrees Celsius, or about 10,000 degrees Fahrenheit). At that temperature, most of the energy the Sun radiates is visible and near-infrared light. At Earth’s average distance from the Sun (about 150 million kilometers), the average intensity of solar energy reaching the top of the atmosphere directly facing the Sun is about 1,360 watts per square meter, according to measurements made by the most recent NASA satellite missions. This amount of power is known as the total solar irradiance. A watt is measurement of power, or the amount of energy that something generates or uses over time. How much power is 1,360 watts? An incandescent light bulb uses anywhere from 40 to 100 watts. A microwave uses about 1000 watts. If for just one hour, you could capture and re-use all the solar energy arriving over a single square meter at the top of the atmosphere directly facing the Sun—an area no wider than an adult’s outstretched arm span—you would have enough to run a refrigerator all day. The Earth absorbs radiant energy from the Sun in the form of visible light. In response, the Earth’s surface increases in temperature (avg. KE) and reradiates this energy in the infrared range. Visible light is not absorbed by atmospheric greenhouse gases (CO2, H2O, N2O, CH4), but infrared light is, producing atmospheric and planetary warming known as the greenhouse effect. From Sun From Earth Visible light range Infrared Light Range

http://earthobservatory.nasa.gov/Features/EnergyBalance/page2.php