A comprehensive presentation of subchapter 2.1 Local Energy Budgets, from the second chapter of Physical Geography, AS Cambridge, Atmosphere and Weather.

1. ASGEOGRAPHYREVISION
ATMOSPHEREANDWEATHER
2.1 LOCALENERGYBUDGETS

2. KEYTERMSANDDEFINITIONS
Albedo is a measure of the reflectivity of a surface normally expressed
as a value between 0 and 100 per cent; for example, fresh snow (highly
reflective) has an albedo of 80–85 per cent, whereas grassland has an
albedo of 20–25 per cent.
Atmosphere is the mixture of gases, predominantly nitrogen, oxygen,
argon, carbon dioxide and water vapour, that surrounds the Earth.
Climate is the average weather conditions of a place or an area over a
period of years.
Conduction is the transfer of heat by contact.
Convection is the transfer of heat by the movement of a gas or liquid.

4. KEYTERMSANDDEFINITIONS
Latent heat transfer is the transfer of energy via evaporation and
condensation. When water is turned into water vapour, heat energy is
used up. In contrast, when water vapour becomes a liquid, heat is
released.
Sensible heat transfer refers to the movement of parcels of air into and
out of the area being studied; for example, air that is warmed by the
surface may begin to rise (convection) and be replaced by cooler air.
This is known as convective transfer. It also includes horizontal
transfers of energy.

5. KEYTERMSANDDEFINITIONS
Inversion is a situation in which cold air is found closer to the ground
and warmer air is found above it; it is common in valleys and basins in
which the dense cold air sinks, displacing the warm air.
Radiation is the emission of electromagnetic waves such as X-ray and
short- and long-wave; as the Sun is a very hot body, radiating at a
temperature of about 5700 °C, most of its radiation is in the form of
very short wavelengths such as ultraviolet and visible light.

6. KEYTERMSANDDEFINITIONS
Long-wave radiation is radiation from a relatively cold body, such as
the earth (infra-red radiation is long-wave radiation that humans
perceive as heat).
Short-wave radiation – also known as ultra-violet radiation – is
radiation from a very hot body, such as the Sun or a microwave oven. It
travels in very short wave-lengths.
Weather is the state of the atmosphere at a given time and place.

7. TOPICSUMMARY
An energy budget refers to the amount of energy entering a system,
the amount leaving the system and the transfer of energy within the
system.
Phenomena vary from small-scale turbulence and eddying (such as
dust devils), which cover a small area and last for a very short time, to
large-scale anticyclones (high pressure zones) and jet streams, which
affect a large area and may last for weeks.

9. TOPICSUMMARY
There are six components to the daytime energy budget: incoming
solar radiation (insolation), reflected solar radiation, surface
absorption, latent heat (evaporation), sensible heat transfer and long-
wave radiation.
Incoming solar radiation (insolation) is the main energy input and is
affected by latitude, season and cloud cover.
The proportion of energy that is reflected back to the atmosphere is
known as the albedo. The albedo varies with colour – light materials
are more reflective than dark materials.

11. TOPICSUMMARY
Long-wave radiation refers to the radiation of energy from the Earth (a
cold body) into the atmosphere and, for some of it, eventually into
space.
The night-time energy budget consists of four components: long-wave
Earth radiation, latent heat transfer (condensation), absorbed energy
returned to Earth (sub-surface supply) and sensible heat transfer.

13. TOPICSUMMARY
Absolute humidity refers to the amount of water in the atmosphere.
For example, there may be 8 g of water in a cubic metre of air. Relative
humidity refers to the water vapour present expressed as a percentage
of the maximum amount air at that temperature can hold.
Mist and fog are cloud at ground level. Mist is classified as when
visibility is between 1000 m and 5000 m; fog is when visibility is below
1000 m.
The relative increase in temperature with height in the lower part of
the atmosphere is known as a temperature inversion (or radiation- or
nocturnal-inversion).

15. ADDITIONALWORK
1. Describe and explain the components of the local energy budget.
2. Under what conditions do mist and fog form?
3. Comment on the importance of temperature inversions.
4. Describe and explain the variations in night-time and daytime energy
budgets as shown in Figure 2.11 in the book.

16. SUGGESTEDWEBSITES
http://education.gsfc.nasa.gov/experimental/all98invProject.Site/Pag
es/trl/inv2-1.abstract.html for a NASA site on local energy budgets.
www.emetsoc.org/annual_meetings/documents/2009/AW4_EMS200
9-548.pdf for Hydrological and Energy Budgets in the alpine area during
present and future climate.
http://onlinelibrary.wiley.com/doi/10.1111/j.1600-
0870.1983.tb00183.x/pdf for the atmospheric energy budgets over
North America, the North Atlantic and Europe based on ECMWF
(European Centre for Medium-Range Weather Forecasts) analyses and
forecasts.