Environmental Science 101
Solar Environment & Interactions

Revolution of the Earth

The Earth revolves around the Sun
1 sidereal year = __________ days
1 tropical year = __________ days
The orbit is an elliptical path
The orbit defines a plane - Ecliptic Plane
Average orbital velocity = 29.8 km/s
Orbital length = 940,416,480 km
Closest approach to the Sun = 147 million km
Farthest distance from the Sun = 152 million km

Rotation of the Earth

The Earth rotates on its axis One complete rotation = one day 1 day = ___________
Equatorial mean rotational velocity = 0.4651 km/s

Tilt of the Earth

Axis is tilted relative to the ecliptic - 23.5 degrees (23°27') from a perpendicular to the ecliptic
The axial tilt varies between:

Precession of the Axis

At present the Earth's axis appears to point towards Polaris (North Star)
Over time the axis moves - precesses


Seasons are caused by variations in the amount of solar radiation received
Controlled by two main factors
Seasons begin/end at an Equinox and Solstice

Incoming Solar Radiation

Radiation transmitted by the Sun and received on Earth:
Earth only receives radiation from the Sun on one half of the sphere.
9% ultraviolet radiation
41% visible radiation
50% infrared radiation

Outgoing Radiation: Earth into Space

Approximately 1/3 of all incoming radiation is reflected directly back into space.
Visible, IR and UV radiation are absorbed by Earth, reemitted as infrared radiation.
Radiation is lost to space on both the night side and day side of the sphere.
Three major dips in the outgoing radiation curve occur.
Water and carbon dioxide absorb certain wavelengths of infrared radiation, blocking it from escaping into space.

Heat Budget

Global Radiation Balance: The amount of incoming solar radiation equals the amount of outgoing radiation.
Changes in the amounts of incoming radiation vs. outgoing radiation can have dramatic effects on the global climate.

Incoming Solar Radiation

What happens to solar radiation?

Greenhouse Effect

A system in which shortwave radiation is allowed to enter freely and is absorbed, then is re-radiated as longwave infrared radiation. The longwave radiation is then retained within the system.
Important greenhouse gases:
H2O Water
CO2 Carbon Dioxide
CH4 Methane
Nitrous oxide (N2O)
Ozone (O3)
Chlorofluorocarbons (CFCs)
Hydrofluorocarbons (HFCs)

Radiation Pathways

Incoming Radiation
Outgoing Radiation

Net Radiation

The Global Energy Balance is a global average.
Radiation is only received on one half of the globe.
Energy is being lost on all parts of the globe.
Equatorial regions receive more radiation than polar regions.
Polar regions loose more radiation than they receive.
Excess energy from the equator must be moved to the polar regions.