A & W xtra Flashcards
Define energy budget
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.
Define albedo
The proportion of energy reflected back to the atmosphere.
Explain how albedo varies with colour.
Light materials are more reflective than dark materials. Grass has an average albedo of 20-30%, meaning that it reflects about 20-30% of the radiation it receives.
Energy that reaches the Earth’s surface has the potential to heat it. Explain how to depends on the nature of the surface.
If the surface can conduct heat to lower layers, the surface will remain cool. If the energy is concentrated at the surface, the surface warms up.
The heat transferred to the soil and bedrock during the day may be released back to the surface at night. This can partly offset the night-time cooling at the surface.
Define Sensible heat transfer
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.
Explain sensible heat transfer affects the day-time and night-time energy budget.
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 is very common in warm areas in the early afternoon.
Sensible heat transfer is also a part of the night-time energy budget: cold air moving into an area may reduce temperatures, whereas warm air may supply energy and raise temperatures.
Define long-wave radiation
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.
Explain how radiation affects the day-time energy budget.
The difference between radiation of energy from the Earth (a cold body) into the atmosphere, and for some of it, eventually into space & the downward movement of long-wave radiation from particles in the atmosphere is known as the net long-wave radiation balance.
During the day, outgoing long-wave radiation transfer is greater that incoming long-wave radiation transfer, so there is a net LOSS of energy from the surface.
Explain how long-wave radiation affects the night-time energy budget.
During a cloudless night, there is a large loss of long-wave radiation from the Earth. There is very little return of long-wave radiation from atmosphere, due to the lack of clouds. Hence there is a net loss of energy from the surface.
In contrast, on a cloudy night the clouds re-radiate long-wave radiation to the surface, hence the overall net energy loss is reduced. Thus, in hot desert areas, where there is a lack of cloud cover, the loss of energy at night is maxmised.
Explain how latent heat transfer effects the day-time and night-time energy budget.
When water is present at a surface, a proportion of energy available will be used to evaporate it, and less energy will be available to raise local energy levels and temperatures.
During the night, water vapour in the air close to the surface can condense to form water, since the air has been cooled by the surface. When water condenses, latent heat is released.
Define Dew.
How does dew affect the energy budget.
Dew refers to condensation on a surface.
The air becomes saturated generally because the temperature of the surface has dropped enough to cause condensation.
Occasionally, condensation occurs because more moisture is introduced, for example by a sea breeze, while the temperature remains constant.
Explain how greenhouse gases affect the energy budget.
The insolation received by the Earth will be reradiated as long-wave radiation. Some of this will be absorbed by water vapour and other greenhouse gases, thereby raising the temperature.
Explain how ground-surface temperatures can vary in the between day and night.
During the day, the ground heats air by radiation, conduction, and convection. The ground radiates energy and the air received more radiation than it emits, the air is therefore warmed.
Air close to the ground is also warmed through conduction.
Air movement at the surface is slower due to friction with the surface, so there is more time for it to be heated. The combined effect of radiation and conduction is that the air becomes warmer, and rises as a result of convection.
At night, the ground is cooled as it emits long-wave radiation.
Define radiation.
The emission of electromagnetic waves such as X-ray, short- and long-wave; as the Sun is a very hot body, radiating at a temperature of about 5700oC, most of its radiation is in the form of very short wavelengths such as ultraviolet and visible light.
Define convection.
The transfer of heat by the movement of a gas or liquid.
Define conduction.
The transfer of heat by contact.
Describe how incoming radiation is absorbed by the atmosphere.
(The Earth’s energy budget)
Of incoming radiation, 19% is absorbed by atmospheric gases, especially oxygen and ozone at high altitudes, and carbon dioxide and water vapour at low altitudes.
Describe how incoming radiation is reflected by the atmosphere
Reflection by the atmosphere account for a net loss of 8%, and clouds and water droplets reflect 23%. Reflection from the Earth’s surface (planetary albedo) is generally about 6%.
About 36% of insolation is reflected back to space.
What percentage of insolation at the top of the atmosphere actually gets through the Earth’s surface.
46%
Describe the variations in the receipt of solar radiation with latitude and season.
There is an excess radiation (+ve budget) in the tropics; a deficit of radiation (-ve balance) at higher latitiudes. However, neither region is getting progressively hotter or colder.
This is because of the horizontal transfer of energy from the equator to the poles takes place by winds and ocean currents. The horizontal transfer between low latitudes and high latitudes to compensates for the differences in global insolation.
Explain why areas close to the equator receive more heat than area that are close to the poles.
-Incoming solar radiation (insolation) is concentrated near the equator, but dispersed near the poles. At the equator, the overhead sun is high in the sky, so the insolation received is of a greater intensity. At the poles, the overhead sun is low in the sky, so the quality of the energy received is poor.
-Insolation near the poles has to pass through a greater amount of atmosphere and there is more chance of it being reflected back out to space. In addition, albedo is higher in polar regions as snow and ice are very reflective, and low-angle sunlight is reflected from water surfaces.
There is much more land in the northern hemisphere compared to the southern hemisphere.
Use statistics to show this.
Explain how this affects temperatures
Oceans cover about 50% of the Earth’s surface in the northern hemisphere but about 90% in the southern hemisphere.
Land heats and cools more quickly than water (it has a lower specific heat capacity). It takes five times as much heat to raise the temperature of water by 2Oc as it does to raise land temperature.
Therefore, a large volume of water is heated for every unity of energy than the volume of land, so water takes longer to heat up.
Why does water heat more slowly?
-Water is clear, so the Sun’s rays penetrate to great depth, distributing the energy over a wider areas.
-Tides and currents cause heat to be further distributed.
What are ocean currents caused by?
Surface ocean currents are caused by the influence of prevailing winds blowing steadily across the sea.
Explain the pattern of ocean currents.
The dominant pattern of surface ocean currents (know as gyres) is roughly a circular flow.
The pattern of these ocean currents is CLOCKWISE in the northern hemisphere and ANTI-CLOCKWISE in the southern hemisphere.
Within the circulation of the gyres, water piles up into a dome. The effect of the rotation of the Earth causes the water in the oceans to push westward; this piles up water on the western edge of ocean basins.
The return of flow is often narrow, fast-flowing currents such as the Gulf stream.
Explain how the Gulf Stream effects temperatures.
The Gulf Stream transports heat northwards and and then eastwards across the north Atlantic; the Gulf Stream is the main reason that the British isles have mild winters and relatively cool summers.
Explain how warm ocean currents effect temperature.
Warm currents from equatorial regions raise the temperature of polar areas (with the aid of prevailing westerly winds). However, this effect is only noticeable in the winter. For example, the North Atlantic Drift raises the winter temperature of north-west Europe.
Explain how cold ocean currents effect temperature.
Cold currents such as the Labrador Current off the north-east coast of North America may reduce summer temperatures, but only if wind blows from the sea to the land.
Explain how ocean currents affect pressure.
In the Pacific Ocean, there are two main atmospheric states.
The first is warm surface water in the west with cold surface water in the east; the other is warm water surface in the east with cold in the west.
In both cases, warm air causes low pressure. As air blows from high pressure to low pressure, there is movement of water from colder areas to the warmer area.
These winds push warm surface water into the warm region, exposing colder deep water behind them and maintaining the pattern.
Explain how the ocean conveyer belt effects the transfer of energy.
In the oceanic conveyor-belt model, surface currents bring warm water to the North Atlantic from the Indian and Pacific Oceans.
This water then sinks and starts the reverse convection of the deep ocean current.
The amount of heat given about of the third energy that is received.
This pattern is maintained by salt; the North Atlantic is warmer than the North Pacific, so there is proportionally more evaporation there.
The water left behind by evaporation is saltier and therefore much denser, which causes it to sink.
Eventually, the water is transported into the Pacific where it picks up more water and density is reduced.
Explain the cause of air motion?
(Factors affecting air movement).
The basic cause of air motion is the unequal heating of the Earth’s surface. The major equalising factor is the transfer of heat by air movement. Variable heating causes variation in pressure and this in turn sets the air in motion.
There is thus a basic correlation between winds and pressure.
Explain how the pressure gradient affects air movement.
This driving force is the pressure gradient; that is, the difference in pressure between any two points. Globally, very high pressure conditions exist over Asia in winter due to low temperatures.
Cold air contracts, leaving room for adjacent air to converge at high altitude, adding to weight and pressure of the air.
By contrast, the mean sea-level pressure is low over continents in summer.
High surface temperatures cause atmospheric expansion and therefore a reduction in air pressure.
High pressure dominates at around 25oC-30oC latitude. The highs are centred over the oceans in summer and over the continents in winter - whichever is cooler.
Define the Coriolis force.
The Coriolis force is the deflection of moving objects caused by the easterly rotation of the earth.
Explain the Coriolis force affects air movement.
Every point on the Earth completes one rotation every 24 hours. Air near the equator travels a much greater distance than air near poles. Air that the originates near the equator is carried towards the poles, taking it with a vast momentum.
The Coriolis force deflects moving objects to the right of their path in the northern hemisphere and to the left of their path in the southern hemisphere.
The balance of forces between the pressure gradient and the Coriolis force is known as the geostrophic balance and the resulting wind is known as geostrophic wind.
The centrifugal force acts at right angles to the wind, pulling objects outwards, so for given pressure, airflow is faster around a high pressure.
How does friction effect the Coriolis force.
Friction decreases wind speed, so it decreases the Coriolis force, hence the air is more likely to flow to low pressure.
Briefly explain the general circulation model.
-warm air is transferred poleward and is replaced by cold air moving towards the equator.
-air that rises is associated with low pressure, whereas air that sinks is associated with high pressure.
-low pressure rain; high pressure produces dry conditions.
Explain the role of the Hadley cell.
There is direct heating over the equator. This air here is forced to rise by convection, travels polewards and then sinks at the subtropical anticyclone (high-pressure belt).
Explain how the ITCZ affects air movement.
At the ITCZ, convectional storms lift air into the atmosphere, which increases air pressure near the tropopause, causing winds to diverge at a high altitudes. The winds move out of the equatorial regions towards the poles, gradually losing heat by radiation. As they contract, more air moves in and the weight of the air increases so the air pressure at the subtropical high-pressure zone.
The denser air sinks, causing subsidence (stability)
Define jet streams.
Jet streams are strong, regular winds that blow in the upper atmosphere about 10km above the surface; they blow between the poles and tropics (100-300km/h).
There are two jet streams in each hemisphere - the polar jet is located between the 50°-60° latitude lines in both the northern and southern hemispheres. The subtropical jet is located around the 30° latitude line.
In the northern hemisphere, the polar jet and subtropical jet flow eastwards.
Explain how convectional rainfall occurs.
When land becomes very hot, it heats the air above it.
This air expands and rises.
As it rises, cooling and condensation takes place.
If it continues to rise, rain will fall.
Convectional rainfall is very common in tropical areas and is associated with the permanence of the ITCZ.
Explain how frontal rainfall occurs.
Frontal rain occurs when warm air meets cold air.
The warm air, being lighter and less dense, is forced to rise over the cold, denser air.
As it rises, it cools, condenses and forms rain.
It is most common in middle and high latitudes where warm tropical air and cold polar air converge.
Explain how orographic rainfall occurs.
Air may be forced to rise over a barrier such as a mountain. As it rises, it cools, condenses and forms rain,
There is often a rainshadow effect, whereby the leeward slopes receives a relatively smally amount of rain.
In general, there are increases of precipitation up t about 2km. Above this level rainfall decreases because the air temperature is so low.
Why do temperature inversions happen?
During the day the ground is heated by the sun’s short wave radiation, and then after a short time, the surface heats the air above when it emits long wave radiation.
At night the ground surface and the air lose the heat energy they have absorbed during the day. However, the ground loses heat energy faster than the air as it is a more efficient conductor of heat.
By the end of the night the ground surface is therefore very cold, and the air will be cooled due to close proximity to the surface. However, the air layer above this, will be still warmer as it has cooled at a slower rate than the ground surface, causing a temperature inversion.
What is a land breeze?
A land breeze occurs at night when the land cools faster than the sea at night. This created a situation which is the opposite to day time - where the air above the sea is actually warmer at night than the air above the land. In this case, it is air above the warmer surface water that is heated and rises, pulling in air from the cooler land surface.
Explain what is meant by a sea breeze?
On a warm summer day along the coast, this differential heating of land and sea leads to the development of local winds called see breezes. The land is heated at a faster rate than the sea and so the air above the land is warmer than the air above the sea during the day.
As the air above the land surface is heated by radiation from the Sun , the air begins to expand and rise, being lighter than the surrounding air. To replaced the rising air, cooler air is drawn in from the above the surface of the sea. This is the sea breeze, and can offer a pleasant cooling influence on hot summer afternoons.
