2.2 Global Energy Budget Flashcards
What is the global energy budget?
The atmosphere constantly receives solar energy, but there was always a balance until recently through radiation, convection and conduction. The atmosphere is largely heated from below, as lots of insolation is let through, re-emitted and then absorbed by greenhouse gases.
What are the proportions of the surface and atmospheric energy budget?
Surface: Insolation absorbed - 48% Outgoing radiation: Latent heat 25% sensible heat 5% LW radiation direct to space 12% Absorbed by GHGs in the atmosphere 6%
Energy budget of the atmosphere: gains: Absorbed radiation - 23% Latent heat transfer - 25% Sensible heat transfer - 5% Absorbed LW radiation - 6%
Losses:
Long wave radiation from the atmosphere to space - 59%
What is the general trend of the global energy budget? (latitude)
There is an excess of radiation in the tropics and a deficit at higher latitudes due to variations in global temperature. This is partly due to areas close to the equator receive more intense heat than the poles, due to higher amounts of atmosphere and concentration of insolation.
This creates a temperature gradient as air rises at the equator, forming low pressure areas which fall at the poles as the air sinks so there is high pressure, creating the basic model of circulation.
At areas of low pressure, we get anticyclonic conditions and at high pressure we get cyclonic conditions. The air is unstable at low pressures as heat rises, taking moisture with it creating tropical weather. When it moves to hot low pressure zones it creates a more complex circulation model.
This is also affected by the angle of incidence of the sun as there is a high angle at the equator so concentrated and low angles at the poles, so more energy is lost, scattered or reflected.
There is also higher albedo in polar regions - which may be offset by longer days. This may also be affected by the Earth’s orbit around the sun as it changes the angle of incidence.
Why are there pressure variations?
Pressure is represented by isobars on maps and will always move from areas of high pressure to low pressure.
Surface pressure belts show marked differences between the hemispheres. Over the arctic there is high pressure which is reduced by altitude. The subtropical high pressure belts can be seen over some ocean areas. In the northern hemisphere pressure tends to be more due to continentality leading to high pressure in the winter and low in the summer due to overheating. Pressure also decreases with altitude.
The poles tend to have high pressure, however it is reduced by the altitude. There is an area of subtropical high pressure around 30 degrees in the Hadley cell. Continental areas have high fluctuations - low in summer and high in winter.
At the equator there is low pressure due to high levels of insolation. Pressure is usually lower in temperate areas than subtropical areas - during winter there is high pressure over Canada and Siberia.
What are monsoons?
Monsoons occur when there is a seasonal reversal of winds, causing changes in precipitation. This mainly occurs in Asia as the wind blows from high pressure sea to continental Asia in the winter, but pulls southern trade winds into low pressure areas in the summer. Monsoons always blow from cold to warm regions.
What is the general model of the global energy budget?
100% insolation
48% absorbed by surface
5% scattered by atmosphere, 18% reflected by clouds, 6% reflected by surface.
6% emitted as long wave radiation, 5% sensible heat transfer, 25% condensation, 5% scattered to atmosphere, 14% absorbed by atmosphere, 4% absorbed by clouds causing 59% to be received by the atmosphere where it is then lost to space.
How does altitude affect the global energy budget?
In the troposphere the temperature starts to fall. Furthermore, as less air is in contact with the ground, and air molecules are more spaced out there is less radiation from the ground to the air molecules which heat the air.
What are wind belts?
Wind belts are air masses which are separated from different air masses by frontal zones. The sub tropical high pressure belts are the source regions for warm tropical air masses which undergo lots of heating as heat is moved from areas of surplus towards the poles.
The main winds blow across the globe and are called trade winds, created by pressure cells - the angle of incidence and latitude. The direction is altered by the Coriolis effect which deflects winds right in the northern hemisphere and left in the southern hemisphere.
Winds between the tropics converge on a line known as the intertropical convergence zone (ITCZ) in which winds blow inwards and subsequently rise, forming an area of low pressure along the equator. This also releases vast amounts of latent heat, causing convection. The ITCZ varies in latitude due to movement of the sun. Low latitude winds are easterlies - westerlies dominate between 35 and 60 degrees.
How does the distribution of energy change during the year?
At the equator there is a surplus of energy. In the south there is also a surplus during our winter and a deficit in the north - as we must account for seasonality. In our summer there is a deficit in the south and a surplus in the north.
How does land-sea distribution affect temperature?
The land and sea have different thermal properties. The land heats and cools faster than water - takes 5 times as much heat to raise water by 1 degree than land. This is because water is clear, so rays penetrate to great depth and tides and currents move it about.
As a result, the sea has a moderating effect as it has not yet caught up with the temperature of the land, meaning distance from the sea plays a role in temperature.
Water takes and gives back heat much slower than the land. In the winter, sea air is much warmer than the land so onshore winds bring heat. The continentality effect also comes into play as the land has lower specific heat capacity it heats up and cools faster, so in the summer the inland is much warmer than coastal regions.
In the daytime, there is high pressure and cool air over the sea, which brings cool onshore winds to the warm, low pressure land. In the night time, the sea is warmer and so has lower pressure and so offshore winds go out to sea as the land is cooler.
How do ocean currents affect temperatures?
Ocean currents are regular movements of water in a direction in the ocean, which are either warm or cold. Warm currents lead to warm, moderating weather conditions as the air above is warm, raising temperatures. This can also create heavy rainfall and monsoons and raises humidity and rainfall, which is good for agriculture and development.
Cold ocean currents bring cold water above it and so reduce temperatures on the land. There is also less evaporation and humidity so little rainfall, creating arid conditions and reducing food.
What causes ocean currents?
Ocean currents are mainly caused by prevailing winds in the same direction as they cause friction on the water’s surface. The pattern is roughly a circular flow, clockwise in the northern hemisphere and anticlockwise in the south. Water tends to pile up and push westward onto the western edge causing a fast, narrow current such as the Gulf Stream. The Labrador ocean current goes from Iceland to the US, and the North Equatorial current brings currents back to the US from the UK. Warm currents tend to move northwards and westwards, causing a return of cold flow.
What factors influence currents?
The vertical motion of tides causes water to move horizontally, creating currents. Latitude is also important as cooler currents come from high latitude areas and warm currents come from low latitudes. Since cold water is denser, the warm water drifts towards polar regions and cold waters replace the leaving warm water, creating currents.
The salinity of water also increases this as saltier water is denser and so flows underneath less saline water. For instance, the salty Mediterranean waters flow into the less saline Atlantic, creating a thermohaline circulation model referred to as the Great Ocean Conveyor belt. Thermohaline means it is driven by temperature and salinity.
The general model of the conveyor belt comes from cold salty water in polar regions sinks into the depths and displaces the hot water at the equator. The hot waters give up their heat to the cold winds and currents which then start to sink and create the reverse convection of the deep ocean current. This tends to move towards the Pacific, Indian and Atlantic ocean where hot waters give up their heat to the cold currents which sink and reverse back to polar regions.
This is why the North Atlantic is warmer than the North Pacific, as there are differences in salinity so there is more evaporation - the salty, dense water left behind is then transported to the Pacific.
What factors affect air movements?
Pressure gradients: air will always blow from high to low pressures so the steeper the gradient, the more intense the air movement. High pressure tends to exist over Asia, the tropics, the North and South Poles. However, in the summer, due to continentality, Asia tends to have lower pressure, creating winds which in theory would just blow up and down the Earth without the Coriolis force.
Coriolis force: an apparent deflection of moving objects caused by the easterly rotation of the Earth. Air flowing from high to low pressure is deflected to the right of its path in the NH and the left of its path in the SH, at right angles to the direction. The balance of forces between the pressure gradient and the Coriolis force is known as the geostrophic balance, creating the geostrophic wind - a centrifugal force which pulls the wind outwards and so airflow is faster at high pressures.
What is the Hadley cell?
Hadley cell: Meeting of trade winds in the equatorial belts form the ITCZ, which pick up latent heat as they cross warm tropical oceans and so rise from convection currents, creating a low pressure cell with unstable air.
This air rapidly ascends forming tall cumulonimbus clouds further form due to latent heat release, creating high rainfalls. This air then spreads out by divergence at the tropopause, heading pole wards where it cools, increases in air density and it is diverted by the Coriolis force and so subsides in the subtropics where it descends at 30 degrees, creating high pressure cells known as the sub tropical high pressure zones.
