Download Assignment #2 Energy Transfer in the Atmosphere

Assignment #2
Energy Transfer in the Atmosphere
The Sun’s energy is used for many things. Some of these uses are:
• Food grown by crops exposed to sunlight, or obtained from animals which eat such
crops.
• Solar cells that power satellites, calculators etc.
• Solar water heaters on rooftops.
• Cars use gasoline or other liquid fuels that originate from fossil plants.
• Electricity may be generated by coal--from fossil plants, too.
• Windmills are powered by winds, whose motion is caused by solar heat as
discussed later. (Ocean wave energy also comes from winds.)
• Hydro-electric power comes from water descending from mountains: it was lifted
into rain clouds by the Sun's heat.
• In addition, all the water we drink is distilled by sunlight. Were it not for the Sun,
all water would be salty.
• Sunlight dries laundry strung on a line.
• In some countries, sunlight is used to produce salt from sea-water (in ponds) and
to dry tomatoes, figs, fish etc.
How is the temperature of the Sun related to sunlight?
The Sun radiates because it is hot. All hot objects
radiate, though sometimes the radiation cannot be
seen with the human eye. Radiation is the transfer of
energy by waves. It is how the Sun’s energy reaches
the Earth.
If the Sun constantly heats the Earth, how come the
Earth does not heat up? Three reasons are:
1) The Earth also radiates energy back into space
2) Clouds reflect heat before it reaches the ground
3) Air absorbs energy
Of the Sun’s energy that enters the Earth’s atmosphere,
about 35% is reflected out. The rest, 65%, is either
absorbed by the atmosphere itself, or by the Earth’s
surface. This energy is then circulated around the Earth
in 3 ways: radiation, conduction, and convection.
Convection
Rising air is one way the ground removes heat: it warms
up the air near it, which rises. Later, higher up in the
atmosphere, the air radiates its heat out to space, cools
down and gets denser, then sinks down again, replaced
by warm air that is still rising. This is known as the
convection of heat.
Convection in the atmosphere stops around 10-15
kilometers. What is the layer above that called?
It is called the stratosphere and is pretty stable and
cold. The region below it--where weather is found--is
the troposphere, and the boundary between the two is
the tropopause.
(If you have seen an isolated thunderstorm from a
distance, you might have noted that its top is flattened
and spread out. It is flattened against the bottom of the
stratosphere, which blocks the convection of the storm
from rising any further.)
Convection of heat energy also occurs from moving
molecules. As you know, part of the energy of sunlight
goes into the ground, and some goes into the water.
When water evaporates it carries part of the energy of
sunlight goes to heating the ground, but another part
evaporates water, from the oceans, lakes, rivers and
plants.
Convection can occur in gases and liquids, but not
solids. The particles making up a solid cannot move
from place to place.
Conduction
Conduction occurs when particles bump into each
other. Energy moves through solids by conduction –
even though the particles cannot move from place to
place, the particles do vibrate back and forth. As
temperature increases the movement of the particles
increases because they have more energy.
The Water Cycle
Water is the driving force that determines our weather. Water absorbs
energy from the Sun, and circulates it throughout the Earth.
All of the water on Earth is referred to as the Hydrosphere. This
includes the water in the oceans, lakes, groundwater, and in the
atmosphere.
THE HYDROLOGIC CYCLE as shown below shows the various
pathways of (1) water to the oceans (rivers, glaciers,
precipitation); (2) water into the atmosphere by evaporation
(from falling rain, rivers & lakes, soil, the oceans, transpiration by
plants); and (3) onto the landmasses (by rain, snow). Water
movement/transport occurs through movement of clouds, by
rivers, ocean circulation, groundwater flow, and evaporation.
The bulk of the water is contained in the oceans, which
contain about 30000 times more water than
atmosphere and continents combined, cover
approximately 70% of the Earth's surface and are on
average 3800 m deep. The remainder of the water is
found in ice caps & glaciers (3%), groundwater (1%),
and rivers and lakes (0.01%). The latter two reservoirs
constitute the terrestrial fresh water supply. Thus, only
a very small fraction of the overall water supply is
suitable and available for human use. The water
transfer between these reservoirs is accomplished by
the processes of evaporation, transpiration,
precipitation, and flow of water (following gravity).
As we shall see below, cycling of water through the
atmosphere is an important factor for energy transfer in the
atmosphere.
Every year about 30000 to 40000 cubic kilometers (a cube 3035 km in size) of water move across the surface of the
continents to the oceans, shaping the surface of the
continents. Evaporation by the sun lifts the water into the
atmosphere, and gravity forces rain to fall back on the earth
as well as causing water to move back to the oceans. The
transfer of water vapor from the oceans to the atmosphere
goes hand in hand with the transfer of tremendous amounts
of energy to the atmosphere and is very important for
atmospheric circulation. For this reason atmospheric
circulation and winds can be considered part of the hydrologic
cycle.
Solar energy is the main force behind this. Because
the Earth is a sphere, the Sun’s energy is not uniform
across the planet. In equatorial regions, where the
sun's rays come in more or less straight on, a maximum
amount of heat is received. In polar regions, on the
other hand, the sun's rays come in slanted at a shallow
angle and considerably less heat is received (see
diagram below).
Average Earth surface temperatures. Blue indicates
lowest temperatures (polar regions), red indicates
highest temperatures (around the equator). The data
used for this diagram were collected between January
1985 and December 1992.
As a consequence, the polar regions stay cooler. The
uneven global heat distribution gives rise to convection
currents that attempt to equalize the heat distribution.
This will be discussed in more detail in the next section.