Tuesday, March 24, 2009
Summary Of Atmosphere
Hello Everyone! This will be the Summary of the first half of our Physical Geography Module, IS2104. We have learnt a lot about The Atmosphere of our Earth throughout the entire Term 1.Well, the Atmosphere's structure can be split into 4 sections - Troposphere, Stratosphere, Meosphere and Thermosphere. The Troposhere distributes heat energy throughout the Earth, while the Stratosphere contains the Ozone Layer. The Atmosphere is composed of 21% Oxygen, 78% Nitrogen and 1% Other Gases. Carbon dioxide (<>. The Greenhouse Effect traps heat from the sun in the atmosphere and also helps reflect infared radiation.
Progressing on, we learnt about the Planetary Heat Balance, which is a system that helps to keep Earth in thermodynamic equilibrium. 100 Units of heat energy from the sun enters the Earth. 19 units of insolation are absorbed in the atmosphere(17 by Clouds And Aerosols; 2 By Ozone), 23 units are scattered and subsequenly absorbed by the Earth's surface as diffused insolation, 28 units are absorbed by the surface as direct insolation, and hence the total number of units of heat energy absorbed by both the Earth's surface and atmosphere is 70 units. However, much of this shortwave solar radiation is also lost back to space. 4 units return via surface reflection, 20 units via cloud reflection, and 6 units via back scattering of sunlight, bringing the total loss of shortwave radiation to 30 units.
Longwave radiation also leaves the Earth. 7 units via sensible heat and 23 units via latent heat transfer. Earth's surface also emmits 117 units of longwave radiation, of which 6 are directly lost to space, and 111 units are trapped by greenhouse gases. (NOTE: This is Where Humans are changing the Atmosphere's composition and subsequently causing Global Warming) The Earth's atmosphere emmits 160 units of longwave energy, which comprise 111 units of surface emissions of longwave radiation, 23 units from latent heat transfer, 7 units from sensible heat transfer, and 19 units from the absorption of shortwave radiation by atmospheric gases and clouds. 64 units of atmospheric emissions is lost directly to space, while 96 units travel to the Earth where it is absorbed and transferred into heat energy.
Moving on, we studied rain - types and formation. Adiabatic cooling occurs when air rises, expands and cools. Relief Rain is formed when adiabatic cooling occurs near relief. Air is forced to go over the elevation, it cools, expands, rises and thus results in rain forming on the windward side of the elevtation. Frontal Rain occurs when a warm air mass and cold air mass collide. Warm air comes from the equatorial regions, while cold air comes from the polar regions. When the two air masses collide, warm air is forced to rise, Adiabatic cooling occurs, thus clouds form and rain results. Such rain is found at temperate regions, where cold air and warm air meet. Convectional Rain occurs when warm air rises. The Earth's surface heats up, as it absorbs heat energy from the sun, and the surface of the Earth transfers heat to the air via conduction. When the warm air rises, adiabatic cooling takes place and clouds from, causing convectional rain. Such rain is found at tropical regions, beause it is sufficently warm, and it occurs usually in the afternoon and evening.
Climate basically refers to how warm and wet a particular location is, over a period of time. The former is measured in terms of temperature, and the latter in terms of precipitation. We can use Climographs to describe climate patterns of different locations. The Earth's climate is not uniform throughout, and varies all around. Essentially, the Earth's tilt and shape result in the distribution of Earth's climate. Climates are distributed among lattitudes. It is warm at the equator, and gets cooler as you progress along the lattitudes, towards the poles. At the equator, the sun's radiation is spread over a small area and is hence very intense, resulting in equatorial regions being very warm. Moving away from the equator, the sun's radiation is spread over increasingly large areas and is thus less and less intense, resulting in temperatures turning lower and lower.
The seasons of the Earth are caused by the changing orientation of the hemisphere with regard to the sun, when the Earth revolves around the sun. The Earth is tilted at an angle of 23.5 Degrees, and during 6 months of the year, one hemisphere receives more sunlight than the other. During Solstices, the particular hemisphere receiving more sunlight will officially begin summer, while the other hemisphere will begin winter. During Equinoxes, both hemispheres will have equal amount of sunlight. Equinoxes indicate the time whereby one hemisphere will begin receving more sunlight, and the other, less.
Finally, Mr Heah also taught us about the Global Air Circulation. The Earth can be split into the Polar Cell, Ferrel Cell and Hadley Cell. Warm air from the equator rises and eventually sinks at the polar regions. This would be the Hadley Cell. At the Polar region, air also rises, and this would be the Polar Cell. A third cell exists in between both, and is known as the Ferrel Cell. Almost no air rises from the Ferrel Cell, and there is thus very little precipitation there. Since this is so, there are few clouds above the Ferrel Cell, resulting in unstable and unregulated temepratures that vary drastically with the time of the day A.K.A DESERTS. A final point to note would be that due to Earth rotating from east to west, the pathway of air will swing westwards.
Thank You and I hope this has been beneficial.
Andrew