# Energy Budget of the Earth-Atmosphere System

## Presentation on theme: "Energy Budget of the Earth-Atmosphere System"— Presentation transcript:

Energy Budget of the Earth-Atmosphere System
In the previous lesson you learned that the earth-atmosphere system is in radiative balance; we could also say that it is in energy balance, since the only form on energy that enters or leaves the system is radiation. You also learned that it is the “imbalances” of energy from place to place across the globe that account for atmospheric processes such as the circulation of the winds and ocean currents and that explain the pattern of climates on the globe.

Energy Transfer Conduction -- direct molecular transfer
Convection -- fluids; air or water Sensible heat (temperature) Latent heat (evaporation/condensation) Radiation -- no transfer medium Basic physics – three ways in which energy is transferred from place to place.

Adiabatic Processes This term refers to the warming or cooling of air due to the rise or descent of air. Rising air cools as it expands; descending air wamrs as it compresses.

Just in case you need to understand that relationship between the three temperature scales – Kelvin, Celsius, and Fahrenheit.

This should be self-explanatory: the evaporation of water absorbs energy from the surrounding air; whereas condensation releases energy. The point is that these changes of state of water are significant in the transfer of energy.

Energy associated with phase changes
A more detailed look at the same thing, for whatever it is worth.

Global Energy Balance Inputs = Outputs

The Sunspot Cycle Sunspots indicate constantly changing levels of solar activity; they have been monitored for centuries and there is some thought that they have impact on climate variability.

to the distance squared (inverse square law).
As the distance from the Sun increases, the intensity of the radiation diminishes in proportion to the distance squared (inverse square law). The solar constant is the amount of solar energy received by a surface perpendicular to the incoming rays at the mean Earth–Sun distance and is equal to 1367 W/m2. Solar constant – in whatever units – is a measure of the solar radiation reaching the top of the atmosphere, before it is depleted in its journey through the atmosphere.

Here it is again – global energy balance.

Electromagnetic radiation can be discussed in terms of the wavelengths
Electromagnetic radiation can be discussed in terms of the wavelengths. The only ones that are relevant to weather and climate are Infrared, Visible, and Ultraviolet

The electromagnetic spectrum shows this using the units of micrometers (mm), and it shows the breakdown within the visible portion of the spectrum

Radiation Laws Stefan-Boltzmann Law E = sigma T (4th power)

Hot sun – short wave lengths.

Earth and atmosphere – much cooler than the sun; longer wavelenghts

This depicts that the gas nitrous oxide absorbs significant amounts of radiation in the longer wavelengths, and very rare in the shorter wavelengths.

Methane also absorbs significant amounts of radiation in the longer wavelengths.

Ozone, a version of oxygen with three molecules, is very, very important in absorbing radiation in the ultraviolet portion of the spectrum. It provides a life-protecting shield against the lethal effects of ultraviolet radiation.

Carbon Dioxide – the most important Greenhouse gas – absorbs large amounts of radiation in the longwave portion of the spectrum. That is it “traps” a lot of radiation emitted by the earth surface, and re-radiates back to the surface. This Greenhouse effect is tremendously important in maintaining the warm temperatures we know and love.

This shows all the gases combined
This shows all the gases combined. You see here that much of the solar radiation is NOT absorbed in the atmosphere; rather, mcu of it passes directly on to the surface of the earth. In the infrared (longwave) portion of the spectrum, a much higher percentage is absorbed: The Greenhouse Effect! It is important to remember that the greatest amount of absorption is die to the presence of water vapor; it is indeed the primary Greenhouse gas.

There you go – no atmosphere, no protective layer of the atmosphere; and it would be really, really cold here – we would not be here.

But we do have an atmosphere.

the surface, of which another 5 units are reflected back to space.
Incoming solar radiation available is subject to a number of processes as it passes through the atmosphere. The clouds and gases of the atmosphere reflect 19 and 6 units, respectively, of insolation back to space. The atmosphere absorbs another 25 units. Only half of the insolation available at the top of the atmosphere actually reaches the surface, of which another 5 units are reflected back to space. The net solar radiation absorbed by the surface is 45 units. Read and try to make sense of it – the distribution of solar radiation as it passes through the atmospere.

ALBEDO means reflectivity; the percentage of incoming solar radiation that is reflected back rather than being absorbed. Over water (Global oceans) the degree of reflectivity changes greatly depending on angle of the sun above the surface.

Bottom line, I guess. This is an older global climate graph; did you ever wonder what average global temperature really means, and how it is “measured.”