WEATHER = the state of the atmosphere at a given time and place
CLIMATE = the average weather in a particular place over at least a 30 year period
The atmosphere is a mixture of gases, solids and liquids held in place by gravity, and it can be split into 4 layers differentiated by temperature changes:
TROPOSPHERE:- this zone lies closest to the Earth and is weather processes take place. It displays the highest temperatures as solar radiation warms the Earth's surface which, in turn, warms the air directly above it (via convection, conduction and radiation). However, this effect decreases rapdily with distance away from the surface and air temperature drops by 6.4 degrees Celcius with every 1000m gained in height (= Environmental Lapse Rate or ELR). Wind speeds also increase with increasing altitude as friction with the surface decreases. This is the most unstable layer and contains most water vapour and particulate matter. The end of the troposphere is marked by the TROPOPAUSE which is an isothermal layer where the temperature remains constant, despite the increase in altitude. The tropopause marks the upper limit of the zone of weather and climate and jet streams are found here.
STRATOSPHERE:- this zone is characterised by a steady increase in temperature (known as a temperature inversion) as a result of solar radiation by the ozone layer. The ozone layer absorbs much of the incoming UV radiation that would be harmful to humans otherwise. Wind speeds increase with height towards the STRATOPAUSE.
MESOSPHERE:- temperature declines rapidly to c.-90 degrees Celcius in this zone as there is not water vapour or particulate matter to absorb radiation. It is characterised by very strong winds (often approaching 3000km/hr) and its end is marked by the MESOPAUSE.
THERMOSPHERE:- this is so named because of the increase in temperature resulting from the absorption of UV radiation by the atomic oxygen found at this altitude.
- Latitude greatly affects climate i.e rainforest on the Equator and deserts on the tropics, and its influence on climate affects other things too, arguably like development (think about latitudes at which most developed countries are situated.....)
- Latitude should have the same influence on climate in both hemispheres but it doesn't. Why? Well this is where you can link in tectonics - landmass is not equally distributed between the two hemispheres, with most continents in the Northern Hemisphere. Oceans take longer to heat up than land but are better at retaining heat and so different climates are experienced.
Global Heat Budget
- At high latitudes more radiation is lost as higher latitudes have a higher albedo so reflect the incoming UV radiation back as longwave terrestrial radiation. The 23.5 degree tilt means that at certain times of the year the poles recieve no insolation, whereas the Equator is always subject to intense insolation. Also, due to the Earth's angle of inclination, at the poels twice the area has to be heated and more atmosphere has to be passed through.
= The net result os a surplus of heat at the Equator
BASIC PRINCIPLE OF THERMODYNAMICS:- Heated substances always move away from their source towards cooler areas, hence the Earths circulatory system. This is the basis of both the atmospheric and oceanic circulation. Remember....
---> Substances ALWAYS move from areas of EXCESS to areas of DEFICIT
Factors affecting the heat budget:
- The Solar Constant ---> varies slightly and affects longer-term climatic changes rather than shorter-term weather variations
- Eccentricity of Earth's Orbit ---> the eccentric orbit of the Earth around the sun can cause up to a 6% variation in the solar constant (this is linked to Milankovitch cycles which we get to learn about towards the end of the module!).
- Altitude of the sun in the sky ---> Equator receives intense insolation as UV radiation strikes Earth head on. At higher latitudes is approaches at a more oblique angle meaning there is twice the area to heat up and more atmosphere to pass through.
- Length of night and day ---> 23.5 degree tilt of Earth means that regions near the poles will not receive any insolation at certain times of the year.
- Sphericity and the Sun ---> higher latitudes make a lower anlge to the sun and the atmosphere is thicker whilst the poles are further away from the sun than the Equator