Earth's Energy Balance

current atmospheric composition

78% nitrogen, 21% oxygen, 1% other gases

Atmospheric Composition 4 billions years ago

80% carbon dioxide, 10% nitrogen, 10% water

positive ground heat flux

Heat is transferred downwards when the surface is warmer than the subsurface

negative sensible heat

If the air is warmer than the surface, heat is transferred from the air to the surface creating _______. situation may take place at night, no input of solar radiation. At this time, the ground cools due to longwave emission and the air directly above the surface is warmer.

net longwave radiation

The difference between incoming and outgoing longwave radiation

long wave radiation and green house effect

The energy absorbed at the surface is radiated by the Earth as terrestrial ___________ . The amount of energy emitted is primarily dependent on the temperature of the surface. The hotter the surface the more radiant energy it will emit. The gases of the atmosphere are relatively good absorbers of longwave radiation and thus absorb the energy emitted by the Earth's surface. The absorbed radiation is emitted downward toward the surface as longwave atmospheric counter-radiation (L↓) keeping near surface temperatures warmer than they would be without this blanket of gases. This is known as the ________. (___ absorbed by CO2 and H2O in the atmosphere)

the latent heat of vaporization

The heat used in the phase change from a liquid to a gas is called the _____. We can't sense or feel _____ as it does not raise the temperature of the water molecules.

positive latent heat flux (transfer)

When evaporation is taking place we say there is a _____. surface is losing energy to the air above. Evaporation is a cooling process for a surface because energy is removed from the water as molecules escape the surface. This causes the surface temperature to decrease. You've probably experienced this cooling when water or sweat evaporates from your skin.

one of the reasons why it is cooler near large bodies of water.

When radiation is absorbed by the Earth it will raise the temperature of the surface. But if the surface is water, some of that energy is used in evaporation rather than heating the water. As a result, with equal inputs of energy to land and water surfaces, land will heat up more than water.

positive sensible heat

When the surface is warmer than the air above, heat will be transferred upwards into the air as a _____

atmosphere

a layer of gases surrounding the planet that is retained by Earth's gravity.

net radiation

can be positive, negative, or even zero. Net radiation is a positive value when there is more incoming radiation than outgoing radiation. This typically occurs during the day time when the sun is out and the air temperature is the warmest. At night, net radiation is usually a negative value as there is no incoming solar radiation and net longwave is dominated by the outgoing terrestrial longwave flux. Net radiation is zero when the incoming and outgoing components are in perfect balance, which doesn't occur too often.

greenhouse gases

carbon dioxide and water

scattering by particles in the atmosphere

causes a beam of light to be broken into several weaker beams of light.

temperature gradient

change in temperature over distance

isotherm lines

connect places on graph with the same average temperatures.

clouds

cool the earth's surface during the day but warm it at night

total income solar radiation or insolation

direct and diffuse shortwave radiation accounts for the _______

shortwave radiation

from the Sun penetrates through space to the outer edge of the atmosphere unimpeded by the vacuum of outer space. If one places a surface oriented perpendicular to an incoming beam of light, 1360 W m2 of solar radiation will be received. This value is known as the solar constant but actually varies by a small amount as the Earth-Sun distance changes through the year. When the solar constant is averaged over the entire Earth surface we get a value of 342 W m2. Once solar radiation begins to penetrate through the atmosphere this amount begins to decrease due to absorption and reflection. about 30% solar radiation is reflected back by particles and clouds. The gases of the atmosphere are relatively poor absorbers of solar radiation, and absorb about 20% of what is available at the outer edge of the atmosphere. The remaining solar radiation makes its way to surface as direct and diffuse solar radiation.

a thermal column

is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and an example of convection. The Sun warms the ground, which in turn warms the air directly above it.The warmer air expands, becoming less dense than the surrounding air mass. (2) The mass of lighter air rises, and as it does, it cools due to its expansion at lower high-altitude pressures. It stops rising when it has cooled to the same temperature as the surrounding air. (3) Associated with a thermal is a downward flow surrounding the thermal column. The downward moving exterior is caused by colder air being displaced at the top of the thermal.

the radiation balance of the earth system

is an accounting of the incoming and outgoing components of radiation. These components are balanced (incoming = outgoing) over long time periods and over the Earth as whole. If they weren't the Earth would be continually cooling or warming. However, over a short period of time, radiant energy is unequally distributed over the Earth, resulting in periods of localized heating and cooling.

sensible heat

is heat energy transferred between the surface and air when there is a difference in temperature between them.

principle use of net radiation

is in the phase change of water (latent heat, LE), changing the temperature of the air (sensible heat, H), and subsurface (ground heat, G). these involve non-radiative transfers of heat. That is, conduction or convection/advection are responsible for the transfer of heat (thermal energy), not electromagnetic radiation.

temperature

is proportional to the average speed of the atoms or molecules in an object (matter).

diffuse solar radiation

is shortwave radiation that has been scattered by gases in the atmosphere. Scattering is a process whereby a beam of radiation is broken down into many weaker rays redirected in other directions.

direct solar radiation

is shortwave radiation able to penetrate through the atmosphere without having been affected by constituents of the atmosphere in any way.

annual temperature range

northern hemisphere has a greater temperature range than the southern hemisphere- southern has more water - perhaps why

tropic of cancer

northern latitude 23.5

ground heat transfer

one of the major uses of radiant energy - to warm the subsurface of the Earth. Heat is transferred from the surface downwards via conduction. Like in the case of sensible heat transfer, a temperature gradient must exist between the surface and the subsurface for heat transfer to occur. Heat is transferred downwards when the surface is warmer than the subsurface (positive ground heat flux). If the subsurface is warmer than the surface then heat is transferred upwards (negative ground heat flux).

evaporation

phase change from liquid to gas

albedo

portion of incoming solar radiation that is reflected away by the earth

albedo values

range from 0 for no reflection to 1 for complete reflection of light striking the surface. Albedo can be expressed as a percentage (albedo multiplied by 100). For instance, grass has an albedo of about .23 (range:.15-.25). This means that of the incoming solar radiation that strikes the grass, 23% of it is reflected away. On the other hand, highly reflective surfaces like snow have an albedo upwards of .90, or 90% of sunlight is reflected away. The average albedo of Earth is approximately 0.31 (31%).

tropic of capricorn

southern latitude 23.5

specific heat

the amount of energy needed to raise the temperature of 1 gram of material by 1oC. _____ is different for every substance, a function of the molecular structure. Water has an unusually high ______

net shortwave radiation

the difference between incoming and outgoing shortwave radiation. During the day,____ is a positive value as incoming always exceeds outgoing shortwave radiation. At night, ___ is equal to zero as the Sun is below the horizon.

latent heat

the energy released or absorbed when a substance changes from one state to another (evaporation, condensation and freezing of water).

convection

the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.

wein's law

the peak wavelength of radiation emission is inversely related to the temperature of the emitting (producing) body.That is, the hotter the body, the shorter the wavelength of peak emission. The figure below shows the wavelengths over which the sun and earth emit most of their radiation. The Sun being a much hotter body emits most of its radiation in the shortwave end and the Earth in the longwave end of the spectrum. The maximum wavelength at which a body emits radiation depends on its temperature.

condensation

the phase change from a gas to a liquid. During the phase change, the latent heat that was taken up during evaporation is released from the water molecule and passed into the surrounding air. During this process latent heat is converted to sensible heat causing an increase in the temperature of the air.

conduction

the process by which heat is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material.

negative ground heat flux

the subsurface is warmer than the surface then heat is transferred upwards

continentality

the tendency of land to experience more thermal variation than water, due to the land's lower specific heat capacity.

electromagnetic radiation

travels through space in the form of waves. Unlike heat transfer by convection or conduction, heat transfer by electromagnetic radiation can travel through empty space, requiring no intervening medium to transmit it. The quantity of energy carried in a wave is associated with the height or amplitude of the wave. Everything else being equal, the amount of energy carried in a wave is directly proportional to the amplitude of the wave. The type or "quality" of radiation depends on the wavelength, the distance between successive crests. The greater the distance between wave crests, the longer the wavelength. Different components of the atmosphere absorb different wavelengths of electromagnetic radiation.