2.2 Atmosphere and weather: the global energy budget Flashcards
What is conduction
the transfer of heat by contact
What is convection
the transfer of heat by the movement of a gas or liquid
How does pressure and wind belts transfer heat
The circulation of wind in the atmosphere is driven by the rotation of the Earth and the incoming energy from the Sun. Wind circulates in each hemisphere in three distinct cells which help transport energy and heat from the Equator to the poles. The winds are driven by the energy from the Sun at the surface as warm air rises and cooler air sinks. Heated air occurs in equatorial areas and this rises and then travels towards the poles before descending in the sub-tropical areas.
These cells generate areas of high and low pressure that influence local weather. For example, in areas of high pressure, cooler, denser air descends towards the Earth’s surface. As it does so, the air becomes compressed and less humid. This explains why areas of high pressure are characterised by fair weather and limited precipitation.
These cells also generate belts of wind. The three main wind belts are the Trade Winds, Westerlies, and Polar Easterlies.
The Trade Winds are found between the equatorial low pressure areas and the sub-tropical high pressure areas. They blow from the south east in the Southern Hemisphere and from the north east in the Northern Hemisphere due to the influence of the Earth’s Coriolis force.
The Westerlies are found to the north and south of the Trade winds. The Monsoon winds are an extension of these moving into the northern Indian Ocean and Bay of Bengal.
The Polar Easterlies begin at approximately 60° north and south latitude and reach the poles. When air moves towards the poles, it causes a polar high-pressure zone. Air from this high-pressure zone then rushes toward the low-pressure zone surrounding the sub-polar region. This flow of air is altered by the Earth’s rotation, the Coriolis force, and deflected west, giving them the name easterlies as they come from the east.
How does latitude affect the world patterns of temperature, pressure, and wind
On a global scale, latitude is the most important factor determining temperature. Two factors affect the temperature: the angle of the overhead Sun and the thickness of the atmosphere. At the equator, the overhead Sun is high in the sky, so the insolation received is of a greater quality or intensity. At the poles, the overhead Sun is low in the sky, so the quality of energy received is poor. Secondly, the thickness of the atmosphere affects temperature. Energy has more atmosphere to pass through at the higher latitudes, so more energy is lost, scattered or reflected by the atmosphere than at the equator, therefore temperatures are lower at higher latitudes than at lower latitudes. In addition, the albedo (reflectivity) is higher in polar regions. This is because snow and ice are very reflective, and low-angle sunlight is easily reflected from water surfaces. However, variations in length of day and season partly offset the lack of intensity in polar and arctic regions. The longer the sun shines, the greater the amount of insolation received, which may overcome in part the lack of intensity of insolation in polar regions. (On the other hand, the long polar nights in winter lose vast amounts of energy).
How does land/sea distribution affect the world patterns of temperature, pressure, and wind
The land and the sea can differ quite markedly in their ability to absorb, transfer, and then radiate heat energy. The sea is much more transparent than the land and so can absorb heat down to a depth of about 10 metres. This heat can then be transferred to deeper depths through the movement of waves and currents.
Also, the sea has twice the specific heat capacity of the land surface. Specific heat capacity is the amount of heat energy that is needed to raise the temperature of 1kg of a substance by 1°C. It is expressed in kilojoules per kg per 1°C.
This means that water needs twice as much energy as the land to raise its temperature by the same amount. Therefore it takes the sea a much longer time to heat up than the land in summer, but, in winter, the opposite occurs as the land loses its heat much more rapidly than the sea This results in the oceans and seas acting as heat or thermal reservoirs and areas close to the sea have a much smaller annual range of temperature than those areas in the centre of continents which are far away from the influence of the seas and oceans.
Areas of land and sea can affect temperatures as a result of their different thermal capacities, ie as the land heats up faster and cools faster than the seas. The result is a greater movement and concentration of isotherms (lines that join points with the same temperatures) over the land masses rather than over the oceans.
As the oceans absorb and store vast amounts of heat, making them warmer than the land masses in winter it results in a shift of the isotherms over the oceans towards the North and South Poles. The war, ocean currents, such as the North Atlantic Drift/Gulf Stream therefore push isotherms north in the Northern Hemisphere winter while the cold Peruvian current pushes isotherms towards the Equator).
How do ocean currents affect the world patterns of temperature, pressure, and wind
Surface ocean currents are caused by the influence of prevailing winds blowing steadily across the sea. The dominant pattern of surface ocean currents (known as gyres) is a roughly circular flow. The pattern of these currents is clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere. The main exception is the circumpolar current that flows around Antarctica from west to east. There is no equivalent current in the northern hemisphere because of the distribution of land and sea there. Within the circulation of the gyres, water piles up into a dome. The effect of the rotation of the Earth is to cause water in the oceans to push westward; this piles up water on the western edge of ocean basins – rather like water slopping in a bucket. The return flow is often narrow, fast-flowing currents such as the Gulf Stream. The Gulf Stream in particular transports heat northwards and then eastwards across the North Atlantic; the Gulf Stream is the main reason that the British Isles have mild winters and then relatively cool summers.
The effect of ocean currents on temperatures depends on whether the current is cold or warm. Warm currents from equatorial regions raise the temperature of polar areas (with the aid of prevailing westerly winds). However, the effect is only noticeable in winter. For example, the North Atlantic Drift raises the winter temperatures of north-west Europe. By contrast, other areas are made colder by ocean currents. Cold currents such as the Labrador Current off the north-east coast of North America may reduce summer temperatures, but only if the wind blows from the sea to the land.
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 surface water in the east with cold in the west. In both cases, the warm surface causes low pressure. As air blows from high pressure to low pressure, there is a movement of water from the colder area to the warmer area. These winds push warm surface water into the warm region exposing colder deep water behind them and maintain the pattern.
