Wednesday, 29 June 2011

Coriolis Effect

I have found that writing this blog really helps me to consolidate what I get taught in lessons and so, seeing as my EPQ is geography related, I thought that I would start writing a bit about some of the things I learn from my research to ensure that I understand them well enough to write 5000 words about it!

My EPQ is based around ocean circulations, something which I have very limited knowledge on, and so I am going to start at the beginning with the basics.......

The Coriolis Effect:

The rotation of the Earth has impacts on the circulation path taken by the winds and the oceans. If the Earth didn't rotate then the atmosphere would circulate to and from the polar regions (areas of high pressure) and the Equator (an area of low pressure) in a continual motion. However, the Earth does rotate.............

The Earth is constantly spinning eastward (anti-clockwise), when looked at from above the North Pole, and the oceans move in the same direction. The circumference of the Earth is greatest along the Equator and so the eastward motion of the Earth's surface, and therefore the oceans, is greatest here. At the poles, where the circumference is at its lowest, the velocity is zero. Therefore, if a volume of water flows north from the Equator, it will maintain the constant eastward momentum but, as it gets closer and closer to the poles, the Earth beneath it will move slower and slower thereby provoking the water to move to the right, in relation to the Earth. This is the Coriolis Effect and its strength increases as the water (or winds) move further away from the Equator. The causes currents of water to turn to the right as they head north from the Equator and to the left as they head south away from the Equator. The distance they are from the Equator dictates how far, to either the right or the left, that they bend, with the currents furthest away from the Equator 'bending' the most. This results in the formation of large circular flows - known as gyres - which flow around all of the major ocean expanses in the world. In the Northern Hemisphere the gyres rotate clockwise and in the Southern Hemisphere, anti-clockwise.

The Coriolis Effect does not only effect ocean currents, but also the atmospheric circulations. In the Northern Hemipshere the air warmed around the Equator rises and flows north, towards the poles. As this warm air moves away from the Equator the Coriolis Effect starts to alter its direction and push it to the right. As it does so, the air starts to cool and then descends where it flows from the northeast to the southwest and back towards the Equator. A similar pattern occurs in the Southern Hemisphere where the winds are blown from the southeast to the northwest where they descend and are then sent back towards the Equator. These winds are the prevailing winds (or trade winds) and they meet at the ITCZ (Intertropical Convergence Zone) where the winds are really calm. Not all the air is forced to descend in either Hemisphere and so, instead, the remaining air carries on towards the poles. This air is known as the westerly winds or the westerlies.

Ekman Spiral
As a consequence of the Coriolis Effect the Ekamn Spiral occurs. Surface water molecules are moved by the winds and as they move, they drag deeper layers of water molecules, located below them, with them. Similarily to the surface water, deeper layers of water are also effected by the Coriolis Effect but, as successive layers of water move slower, a spiral effect is created (the Ekman Spiral) as the different layers of water move slower to the right or left. The movement of water, due to the combination of  the wind direction and surface water movement, is known as Ekman Transport. Ekman Transport produces variations in the height of the sea surface (as it removes water from some areas and builds it up in others) and so causes the surface to slope gradually. This slight sloping of the surface develops  horizontal differences in  water pressure and this pressure gradient leads to geostrophic flow.

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