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Section 4 - Practice 4 - script

I work for the National Weather Service and as part of your course on weather patterns, I've been asked to talk to you about how we predict the weather. We're so used to switching on our TVs and getting an up-to-date weather forecast at any time of day or night that we probably forget that this level of sophistication has only been achieved in the last few decades and weather forecasting is actually an ancient art. So I want to start by looking back into history.

 The earliest weather forecasts appeared in the 1500s in almanacs, which were lists of information produced every year. (31) Their predictions relied heavily on making links between the weather and where the planets were in the sky on certain days. In addition, predictions were often based on information like if the fourth night after a new moon was clear, good weather was expected to follow.

But once basic weather instruments were invented, things slowly started to change. (32) In the mid-fifteenth century, a man called Nicholas Cusa, a German mathematician, designed a hygrometer which told people how much humidity there was in the air. To do this, Cusa put some sheep's wool on a set of scales and then monitored the change in the wool's weight according to the air conditions. A piece of equipment we all know and use is the thermometer. (33) Changes in temperature couldn't really be measured until the Italian Galileo Galilei invented his thermometer in 1593. It wasn't like a modern-day thermometer because it had water inside it instead of mercury. In fact, it wasn't until 1714 that Gabriel Fahrenheit invented the first mercury thermometer. In 1643 another Italian called Evangelista Torricelli invented the first barometer which measured atmospheric pressure. This was another big step forward in more accurate weather predicting.

As time went on, during the seventeenth, eighteenth and nineteenth centuries, all these meteorological instruments were improved and developed and people in different countries began to record measurements relating to their local weather. However, (34) in those days it was very difficult to send records from one part of the world to another so it wasn't possible for them to share their information until the electric telegraph became more widespread. This meant that weather observations could be sent on a regular basis to and from different countries. By the 1860s, therefore, weather forecasts were becoming more common and accurate because they were based on observations taken at the same time over a wide area. (35) In 1863, France started publishing weather maps each day. This hadn't been done before, and other nations soon followed. So that was the start of national weather forecasting and I'll now tell you how we at the National Weather Centre get the information we need to produce a forecast.

Even today, one of the most important methods we use is observations which tell us what the weather is doing right now. Observation reports are sent automatically from equipment at a number of weather stations in different parts of the country, (36) They are nearly all based at airports although a few are in urban centres. The equipment senses temperature, humidity, pressure and wind speed direction.

Meteorologists also rely really heavily on satellites which send images to our computer screens. What we see on our screens is bright colours. (37) Orange represents dry air and bright blue shows moisture levels in the atmosphere. The satellites are located 22,000 miles above the surface of the Earth and it's amazing that despite that distance (38) it's possible for us to make out an individual cloud and follow it as it moves across the landscape.

In addition to collecting data from the ground, we need to know what's happening in the upper levels of the atmosphere. So a couple of times a day from many sites across the country, we send radiosondes into the air. (39) A radiosonde is a box containing a package of equipment and it hangs from a balloon which is filled. with gas. Data is transmitted back to the weather station. Finally, radar. (40) This was first used over 150 years ago and still. is. New advances are being made all the time and it is one method for detecting and monitoring the progress of hurricanes, Crucial information is shown by different colours representing speed and direction. Radar is also used by aircraft, of course. All this information from different sources is put into computer models which are like massive computer programs. Sometimes they all give us the same story and sometimes we have to use our own experience to decide which is showing the most accurate forecast which we then pass on to you. So I hope next time you watch the weather forecast, you'll think about how we meteorologists spend our time. And maybe I've persuaded some of you to study meteorology in more depth.

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