(d) This question relates to precipitation. i. Explain the general processes lea
ID: 116296 • Letter: #
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(d) This question relates to precipitation. i. Explain the general processes leading to precipitation? (4 marks) ii. Carnarvon (on the Western Australian coast at latitude 25o south - see map) has 230mm average annual rainfall while Darwin (on the Northern Territory coast at latitude 12oS) has 1730mm average annual rainfal. With reference to the general circulation (see diagram in question lb) and precipitation processes, explain this difference Darwin Camarvon 4 marks) (Question 1 continued on the next page)Explanation / Answer
i. Precipitation only comes down to the ground after it condenses in the atmosphere. Condensation is when water vapor turns to liquid water. We are surrounded by water vapor - it's an important component of the atmosphere. But if it changes back into liquid water and builds up around dust particles in the air, we get clouds. If the cloud droplets get heavy enough, they fall back to the ground for the very same reason you would - gravity!
Fog is just a ground-level cloud. It's created by water condensing around dust particles low to the ground instead of high in the air. Dew is also condensation, but on objects on the ground like leaves, cars and windows instead of dust particles in the air.
So why does some water fall back to the ground and other stays as a gas in the atmosphere? This has to do with air movement from the ground. When warm air rises quickly into the atmosphere, this is known as an updraft - literally air rising upward. Warm air holds more moisture than cool air, so it takes water up into the atmosphere with it. However, once the warm air rises, it cools and shrinks. The water vapor in the air gets squeezed out as liquid water and builds up around dust particles, forming our cloud.
Usually, clouds do a pretty good job of holding onto their water because they are wider than they are tall. So any falling water droplets only fall a very short distance before being swept back up into the cloud by the updraft.
If the cloud forms vertically, though, this means that the falling water droplets have farther to fall before the updraft gets a chance to whisk them back into the cloud. When this happens, we get the opposite of an updraft, called a downdraft. This is just cool air falling through the atmosphere as it gets dragged down by the falling water.
As you can see, water droplets in clouds are very friendly, and they like to not only take cool air with them, but other droplets as well. As they fall, they pick up other droplets, grow in size and become too heavy once they do finally hit the updraft. This is when gravity takes over and carries these droplets back to the ground as precipitation.
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