![]() ![]() To measure clouds, we need to know how much cloud there is in the sky, what height these clouds are at and what type of clouds these are. These work by firing a beam of light in a straight line and measuring how long it takes to be bounced back, depending on how long this takes will give you the visibility. You can do this yourself at home, if you look out of your window, what can you see? Your neighbour's houses? Some hills? Some tall buildings? Get your parents to help you find out how far away each of these things you can see is, then when you look out your window you will know if the shops 1km away are hard to see, but still just about visible, then you will know the visbility is 1km if you can't see your neighbour's house, which is 50m away, you will know the visbility is less than 50m.Īlthough we do still use our eyes, we also use lasers where there aren't humans to check. To measure visibility we simply use our eyes! We look for 'vis points', these are objects that don't move that we know how far away they are so if we can see them we know that the visbility is at least that far or if we can't see it then we know it is less than that. Visibility is how far we can see often it is many kilometers, but when it is foggy it may only be a few metres. These anemometers are mostly on mountain sites as they can’t freeze like other anemometers can do in very cold conditions. New anemometers use sonar to measure the wind direction and speed at the same time they do this by sending sonar between different sensors and depending on how long it takes for the signal to be received the sensors can tell what speed the wind is blowing at and the direction it is coming from. The next time you are on a long car journey see if you can spot any of these on the side of the road. These are often cups which spin through a beam of light to measure the wind speed and are placed 10m above the ground this height helps avoid any problems with friction from buildings and other objects near the ground. To measure wind speed we use an anemometer, a piece of equipment that, traditionally, would spin when there is wind and how fast it spun would tell you how fast the wind is. This can tell us a lot about the weather, for example, when the wind is coming from the north, it is usually going to be a colder day, when it is coming from the south it is likely to be a warmer day. When we talk about wind direction, we talk about where it has come from, not where it is going. To measure the wind direction, traditionally, we used a weather vane, which would point to the direction the wind was coming from. There are two properties of wind that we measure: direction and speed. Using the temperatures from the two thermometers and equation we can calculate humidity. The wet bulb temperature is measured similarly to the normal air temperature we use a thermometer that has its end wrapped in some damp cloth and it is kept in a Stevenson screen with the thermometer.Įnergy is needed to evaporate the water from the cloth and this causes the air around it to cool a little (from the loss of energy), which means the thermometer measures a lower temperature. We measure humidity, by first measuring the wet bulb temperature and then doing a calculation. Humidity is how much water vapour is stored in the air and is shown as a percentage if the humidity is 100%, the air is saturated meaning it cannot hold any more water - this occurs when it is foggy and sometimes when it is raining, but usually it rains before the humidity gets this high. Stevenson screens face north, which combined with their colour and slats, give us the best measure of the current temperature, without getting too hot in direct sunlight or being too cool in the shade. This is a white box with slats in it to allow air to flow through the box. To measure the temperature accurately we keep our thermometer a Stevenson screens. Instead we now use digital thermometers or alcohol thermometers. ![]() We used to use thermometers that had mercury in them, but all of these are no longer used as mercury is dangerous if it were to leak out or the thermometer was to break. To measure temperature we use a thermometer, you probably have one of these at home for taking your temperature when you are feeling poorly. Temperature is a measure of how much heat energy something has when measuring the weather we usually want to know the temperature of the air. To do this we measure all the different parts of the weather and record it, this is called a weather observation. To be able to make the best weather forecasts we need to know, with as much detail and accuracy as possible, what the weather is doing right now. ![]()
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