climatic controls

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Created on: 20-03-15 20:08

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Describe and explain the major global climatic controls
- There are many fundamental controls on our climate
  - The atmospheric heat budget - the energy we receive from the sun
    - This looks at the distribution of heat energy which the earth receives from the sun, it is the balance between the incoming solar radiation and the outgoing radiation from the planet
    - only 55% of incoming solar radiation reaches the earths surface
    - The rest of the incoming solar radiation is reflected or absorbed by clouds and / or the atmosphere
    - The energy which is absorbed warms the earth and the heat is returned to the atmosphere as long wave, 70% of this energy is lost straight to space.
      - This is because it is radiated to space from clouds and the atmosphere and directly from the earth.
        With the increase of greenhouse gases, the atmosphere is able to absorb more of the outgoing radiation
  - The structure of the atmosphere - the troposphere, stratosphere, mesosphere and thermosphere
    - The structure of the atmosphere is determined by temperature changes with height, 99% of the atmosphere is nitrogen and oxygen, but there is also water vapour, ozone and carbon dioxide.
    - The temperature decreases with height in the troposphere because the suns radiation strikes the earth and the earth then warms the air above it, so the closer it is to the ground the warmer it is.
    - Temperatures decrease with height in the mesosphere because the stratosphere warms the lowest levels of this layer and heat is then slowly recirculated above
    - The temperature increases with height in the stratosphere, because the ozone absorbs uv radiation from the sun
    - Temperature increase with height in the thermosphere because atomic oxygen absorbs radiation.
  - The latitudinal position (N/S)
    - The latitude affects the climate in two ways, the angle of the sun and the length of daylight, the longer the daylight, the greater the insolation
    - In the tropics, the length of daylight is constant at 12 hours. At the poles, in their winter, virtually no direct sunlight reaches them so there is almost 24 hours of darkness. This reduces the temperatures significantly
      - However, in the summer, they have long days and short nights, meaning relatively more direct heating ( still not warm due to the oblique angle of the sun)!
  - The General atmospheric circulation - The Hadley cell model
    - so that the equator and tropics do not become progressively hotter from the suns insolation, a redistribution of heat energy must take place constantly
    - The Hadley cell helps recirculate some of the heat energy in the equatorial regions.
      - This happens when because the suns short wave radiation ( insolation) heats the earth, the earth then warms the above air. This air becomes less dense than its surroundings and therefore begins to rise, as it rises it begins to adiabatically cool, this is when particles spread apart and expand, causing it too cool. Condensation then takes place causing rainfall and culiumbious clouds, as air continues to rise, it is forced right, in the northern hemisphere and left in the southern hemisphere due to the earths rotation and the coriolis affect, eventually the air begins to fall, this causing adiabatic warming, where particles come closer and evaporation of moisture takes place, leaving it ain dry conditions
    - Atmospheric pressure is the force per unit that is exerted against a surface by the weight of the are above. Low pressure areas have a lower atmospheric pressure mass above their location whereas, high pressure areas have more atmospheric mas above their location
    - The Tricellular model
      - As well as the Hadley cell, there are two other atmospheric cells, the Polar cell and the Ferrell cell which operate in a similar manner and help to redistribute heat towards the poles
      - The polar front is the meeting of warm and cold air, this is also the Polar Jet stream
        Their are four jet streams circulating the globe, two each in the northern and southern hemispheres.
        
        Jet streams are currents of fast flowing air moving at over 100mph
        
        They flow in the tropopause from west to east
        
        They are found where temperatures have a vast contrast across short distances,
        It is the large variations in temperatures that provide the energy that drive the narrow stream of powerful winds
        
        The polar jet stream plays a large part in determining the weather of the uk, the rossby waves in the jet stream allow for depressions to form in the Atlantic which bring wet weather to the uk
        
        The air streams are 10km above the surface, there path in the northern hemisphere follows a ridge of high pressure, the cold air from the poles is then carried southwards, until it reaches a trough of low pressure, the warm air is then taken from the tropics and travels northwards, where it again reaches a ridge of high pressure.
        
        When the jet stream is strong, it shifts northwards towards polar altitudes, leaving Britain in a region of relatively high pressure from continental Europe. This leaves us with settled weather with clear skies, in the summer it leaves it very hot but in the winter it causes freezing temperatures, when the jet stream is weak, it meanders widely, and can shift southwards towards the tropics, bringing low pressure weather systems directly across the Uk, leaving very wet conditions
  - The planetary surface winds ( the trade winds )
    - These are major contributor when it comes to transferring energy around the globe
    - Planetary surface winds form when warm air rises, (e.g. forms a low pressure at ITCZ ) and cool air sinks ( e.g. forms high pressure over the subtropical anticyclone ) as it allows sinking air to replace the rising air. The surface winds are simply equalizing the pressure difference. So the NE and SE trade winds which affect countries like brail blow from regions of high pressure to low pressure
    - wind strength is shown by pressure gradients, this is shown by isobars, if they are close together there is a steep pressure gradient, meaning pressure changes quickly, so winds are stronger.
    - The winds influence the surrounding temperature because if they blow off a cold surface they bring colder temperature and vice versa
  - Ocean currents and circulation and confidentiality
    - Ocean currents are set in motion by the prevailing winds blowing over the surface of the ocean, they are also vital in transferring heat from the equator to the poles, the main ocean currents follow circular routes (gyres)
    - Due to the coriolis affect, in the northern hemisphere, these currents travel clockwise, however in the southern hemisphere they travel anti clockwise
    - Warm currents flow along the Westside of the ocean, and cold currents flow along the eastside of the ocean.
    - The Uk benefits from the North Atlantic conveyor ocean transfer
      - The relatively warms waters of the North Atlantic Drift are responsible for moderating the climate of western Europe, so that winters are less cold than would otherwise be expected at that latitude
        Without the warm North Atlantic drift, the UK and other places in Europe, would be as cold as Canada, because it is at the same latitude
        UK temps would be more than 5c colder in the winter
        
        The (Gulf stream/North Atlantic Drift) forms part of the thermohaline circulation (Warm salty water) which is driven by density differences, the warmer, less dese water at the tropics and the colder, denser salty water that sinks in the Noth Atlantic
        The cold subsurface water then travels to the gulf of Mexico, where it warms enough to resurface and flow back north as the gulf stream
        However, global warming could cause this thermohaline circulation to shut down as a result of artic warming which would release more freshwater into the north atlantics so that water is less saline and not dese enough to sink, as a result the climate of Britain would be cooler
        
        However, global warming could cause this thermohaline circulation to shut down as a result of artic warming which would release more freshwater into the north atlantics so that water is less saline and not dese enough to sink, as a result the climate of Britain would be cooler
    - Continentality
      - distance from the sea
      - Continental areas warm up in summer and cool down quicker in winter than coastal areas because land has a low specific heat capacity ( this means it heats up and cools down quickly )
        This creates a more extreme continental climate with a large annual range of temperatures compared with coastal areas which has maritime climate with a small temperature range.
      - The ocean has the opposite influence, water unlike land has a high specific heat capacity, so when it heats up it maintains its heat for a long time. In winter its remains relatively warm, in comparison, during the summer, the reverse is true, and the sea only heats up slowly and is colder than the land, this creates a maritime climate and has a smaller range of temperatures
    - s the Uk is surrounded by water it is inevitable that the climate will be wet, this is made worse by the fact that the water is warm , because this makes the air above the water warm and therefore rise, meaning it begins to adiabatically cool, and eventually condense into rainfall
    - Air which is warm at ground level is deemed to be unstable, this means that it will want to rise, conversely, if air is cooled at low level it is stable, so it wont want to rise and the climate will be dry , so if the ocean currents cool, the ir above it should be dry
    - For example a region effected by cold currents is the western south of America, particularly Peru and Chile, this is affected by the Humboldt current, this means the air above it is stable
      - The climate here is formed because the cold currents cool the air above it, when the ocean is blown onshore, it lowers the temperature meaning air becomes more stable and therefore remaining dry, this has created the coastal desert in the subtropical region
    - La Nina/El Nino
      - There is one more ocean circulation which plays a major impact on the global climate
      - This is the circulation of water across the pacific ocean
      - To understand this we must first understand how sea temperatures vary with depth, as the earths surface is heated from above. It is logical that the upper surface of the ocean is warmer than the underlying layers, the change in temperatures as you descend is sudden in places and this creates a boundary called the thermocline
        However, simple layering system is altered when deep ocean currents rise to the surface
        For example the Humboldt current of the coast of Chile/Peru
      - La Nina is the normal walker cell circulation, it is the idea that the ocean on the east side is cooler than that of the west, this is because there is a pool of warm water in the west kept in place by the strong trade winds, this means the air above it is unstable and therefore begins to rise, meaning their is wet weather in this region.
        El Niño is when this is reversed or when trade winds die down, this allows the pool of warm water to drift over to the east, meaning the air here is unstable and eventually rise, meaning their is wet weather at the east side and dry weather at he west
        EL NINO IS THE REVERSAL OF LA NINA, IT OCCURS EVERY 2 TO 7 YEARS, IT AFFECTS THE CONDITIONS ACROSS THE PACIFIC BUT ALSO IMPACTS THE RST OF THE WORLD
        in early 2010, there was an el nino, event which resulted in, eavy rainfall and landslides in peru, fires in Sydney and a lack of snow in Vancouver for the winter games ( too warm and wet)
        Untitled
        
        EL NINO IS THE REVERSAL OF LA NINA, IT OCCURS EVERY 2 TO 7 YEARS, IT AFFECTS THE CONDITIONS ACROSS THE PACIFIC BUT ALSO IMPACTS THE RST OF THE WORLD
        in early 2010, there was an el nino, event which resulted in, eavy rainfall and landslides in peru, fires in Sydney and a lack of snow in Vancouver for the winter games ( too warm and wet)
        Untitled
  - The Altitude (height)
    - The effect of altitude on the climate is more useful for explaining local variations in climate
      - In the Uk, relief rainfall occurs when moist air is forced to rise over mountains, warm moist, unstable air that comes from the sea, is forced to rise when approaching a hill, as it rises it starts to adiabatically cool and therefore condense, meaning in this areas there will be large clouds and high amounts of rainfall, once it has reached the pek of the mountain, it will start to sink, as it sinks it adiabatically warms and as it can no longer hold the moisture its evaporates leaving dry conditions this is called the rain shadow,
    - The altitude also has an effect on temperature
      - In normal circumstances, with height, temperatures fall. As you gain height there is a fall in pressure, and this means the molecules are further apart, this means there is a fall in temperatures as there is less kinetic energy between the particles.
        The fall in temperatures with height in the troposphere is called the environmental lapse rate, which is roughly 6.5c per 1000m.
        
        Within the overall environment, pockets of warmer air rise and cool as they expand, until they are in equilibrium with the ELR. Alternatively pockets of colder air sink and gain temperatures as they are compressed until they are in equilibrium with the ELR
        Rising pockets of air cool at the adiabatic lapse rate, however the rate at which they cool depends on whether the air is dry or saturated, if the dry air is forced to rise, the expansion in volume causes a temperature fall of approximately 10c per 100m, this is the dry adiabatic lapse rate
        Conversely if the air is saturated, and condensation is taking pace there is a release of latent heat, this reduces the rate of cooling to 5c per 1000m this is called the saturated adiabatic lapse rate.
  - Together they overlap and interact to produce what we call our weather (day to day changes in the atmosphere) and climate ( average weather over an area, including seasonal patterns and change over years )

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climatic controls

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