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  1. 1. 1Weather UnitWeather UnitWhether itis climateor not?
  2. 2. 2Today we will look at …Today we will look at …1. What makes weather?2. How do we measure weather?3. Why do we need forecasts?4. Are the forecasts any good? (that’shomework)
  3. 3. 3What is the weather?What is the weather?Weather is the condition of theair around us over a shortperiod of time (from day to day)
  4. 4. 4The elements of weatherThe elements of weatherTemperature (the amount of heat)Precipitation (water – rain, sleet, hail,snow)Wind speedWind directionCloudsAir pressureVisibility (How far can you see?)
  5. 5. 5TemperatureTemperatureThis is a measure ofhow hot or cold it is.We can tell this bylooking at the clothesthat people wear.
  6. 6. 6PrecipitationPrecipitationWater in the air fallsto the ground in oneof several formsRainSnowSleetHailBut also ice and fog
  7. 7. 7Wind SpeedWind SpeedThis tells us howstrong the wind is.We can get a goodideas of this bylooking at smokeand trees.
  8. 8. 8Wind directionWind directionThis is thedirection fromwhich the windblows – it ismeasured by awind vane
  9. 9. 9Cloud TypeCloud TypeClouds come in manyshapes, sizes andheights – more aboutthat next week
  10. 10. 10Cloud CoverCloud CoverThis is the amount ofthe sky covered bycloud. It ismeasured in eighthsClear sky4/88/8 (Total cover)
  11. 11. 11VisibilityVisibilityThis is the distancethat can be seen. Itis measured inmetres.
  12. 12. 12Measuring WeatherMeasuring WeatherWhy do we measure the weather?Weather can be described using terms such as wet orfine, warm or cold, windy or calm, so why is there aneed to measure the weather?For most people, a description of the weather isadequate but for many businesses more detailed andaccurate measurements are required.The science of studying weather is called meteorology.Weather scientists or meteorologists measuretemperature, rainfall, pressure, humidity, sunshine andcloudiness and they make predictions and forecastsabout what the weather will do in the future.This is important for giving people advance notice ofsevere weather such as floods and hurricanes – or even‘Can I go out without my raincoat tomorrow?’Who else mightfind a forecastuseful?
  13. 13. 13Measuring temperatureMeasuring temperatureThe hotness or coldness of a substance is called itstemperature and is measured with a thermometer. Theordinary thermometer consists of a hollow glass bulbattached to a narrow stem with a thread-like bore.The bulb is filled with liquid,– If it is silver it is mercury– If it is red it is alcoholThe liquid in the tube expands when the temperaturerises and contracts when the temperature falls. Theamount of expansion and contraction is measured by anumbered scale.Whilst thermometers are really measuring their owntemperature, they are used to measure thetemperature of the surrounding air.To make sure that the temperature of the surroundingair is the same as the thermometer, it must be shadedfrom sunlight and be exposed to adequate ventilation.These conditions are provided by a Stevenson screen.
  14. 14. 14A Stevenson screenA Stevenson screenWhy do we needone of these?Why does ithave legs?Why is it paintedwhite?Why has it got such a largeroof?What are thelittle gaps inthe side for?(louvers)
  15. 15. 15Measuring temperatureMeasuring temperatureMost temperature scales today areexpressed in degrees Celsius (°C),although you will sometime seeFahrenheit (°F) in use.The Celsius scale is fixed by two points,the freezing and boiling point of water,which at sea level are 0°C and 100°Crespectively.The scale is then divided into 100 units.
  16. 16. 16Measuring TemperatureMeasuring TemperatureThis is a maximum-minimumthermometer.This type of thermometermeasures both the highest(maximum) and lowest (minimum)temperature over a period of time,usually one day (24 hours).Recording temperature with amaximum-minimum thermometerThere are two markers, one forthe maximum temperature and onefor the minimum. The mercury inthe tube pushes the markers astemperatures go up or down.
  17. 17. 17Measuring TemperatureMeasuring TemperatureThe temperature tends to be highest aroundthe middle of the day, when the sun is at itshottest – even if you cannot see it because it iscloudyThe temperature is coldest during the nightSo if you leave a maxi-min thermometer for 24hours you will get the maximum and theminimum and be able to find the daily range(the difference between the 2)The difference between the daily maximumand the daily minimum temperature is thediurnal range.
  18. 18. 18Looking at the first 2 rows on theLooking at the first 2 rows on theWSWSWhat does a thermometer do?How does it work?What does a maxi-min thermometer tellyou?What is diurnal range?What does a Stevenson screen do?How does it work?
  19. 19. 19Wind speedWind speedWind is moving air.Wind can be measured by its speedand the direction from which it hascome.The speed of the wind can bemeasured using a weather instrumentcalled an anemometer.The speed can be recorded in manydifferent units, including forexample:– miles per hour;– kilometres per hour;– metres per second;– knots;– the Beaufort Scale (we will learn aboutthis one next week)This one hasa weathervane on itunderneath.What doesthat tellyou?
  20. 20. 20Wind directionWind directionThe direction of the wind is expressed as thepoint on the compass from where the wind isblowing.If a wind is blowing from the south, it istravelling northwards but is called a southerlywind.Wind direction can be measured in manydifferent ways; using a weather vane or simplyholding a light object such as a flag or ribbon.On your sheet, write down what they aresmelling!!
  21. 21. 21Wind directionWind directionKnowledge of wind direction is importantfor many people and activities.For example aircraft need to take offfrom the end of the runway which isgoing into the wind for extra lift attake-offWind direction is of course veryimportant for leisure activities such asyachting.Can you think of anything else whereknowing the wind direction is important
  22. 22. 22For the WS…For the WS…What is an anemometer for?How does it work?What is a weather vane for?How does it work?
  23. 23. 23Air pressureAir pressureAn instrument called abarometer is used tomeasure the pressure ofair.Although air is very light,because the atmosphere isso thick (many kilometres inaltitude above the Earthssurface), air exerts a forceor pressure.When air is cooled it sinkstowards the ground, thepressure increases and ahigh pressure is measured.When the air warms up itrises, the pressure isreduced and low pressure ismeasured.This is what goes oninside a barometer
  24. 24. 24Air pressureAir pressureWhy do we need to knowabout pressure?High pressure gives usclear skies which means itis hot in the summer andcold in the winterLow pressure gives uscloudy skies and rain. Wehave lots of low pressureover the summer in the UK!
  25. 25. 25For the WSFor the WSWhat is a barometer for?How does it work?What is weather like if the pressure ishigh in summer?What is the weather like if the pressureis low?
  26. 26. 26Measuring liquid precipitationMeasuring liquid precipitationWhat varieties of precipitation arethere?Which types are NOT liquid?Why do you think that if we measuredthis one, that we might not use the sameinstrument as the liquid one?
  27. 27. 27This is the rain gauge used by theThis is the rain gauge used by theMet OfficeMet Office Why do youthink the actualfunnel is inside acopper cylinder– not a the top?Why is the bottlethat stores the waterunderground?How does themeasuring gaugeon the right work?
  28. 28. 28For the WS…For the WS…What is a rain gauge for?What kind of precipitation does it notcollect?
  29. 29. 29Weather is important to usWeather is important to usThings that are affected by weather– farming– sport– transport– the amount of energy we use– work– tourism
  30. 30. 30So we need weather forecastsSo we need weather forecastsInformation iscollected by– weather stations– schools havethem
  31. 31. 31So we need weather forecastsSo we need weather forecastsInformation is alsocollected byBy shipsAircraftSatellitesand then themeteorologists usethe information theyhave to predict theweather over thenext few days
  32. 32. 32Weather from the met officeWeather from the met officeFriday’s map from
  33. 33. 33Weather from the met officeWeather from the met officeThis was the windmap. The numbersmeasure in miles perhour with direction itis blowing to
  34. 34. 34Weather from the met officeWeather from the met officeThis was theTemperature map.The numbersmeasure in degreescentigrade
  35. 35. 35And BBC weatherAnd BBC weatherFrom used to show it all onbut now they just showwhere the cloud is!!
  36. 36. 36And weather onlineAnd weather onlineFrom show it allexcept the windspeed anddirection!!
  37. 37. 37Symbols aredifferent butonce you get theidea…So what is theweathersupposed to belike in each ofthese places?
  38. 38. 38HomeworkHomeworkGo to (hopefully now!) either UK oryour continentIf it is the UK, clickon your regionDo not go moredetailed than thatIf a continent, pickwhich part, then pickyour country
  39. 39. 39Now you have got your weatherNow you have got your weatherforecastforecastLook out each day – how good was theforecast?If you have a thermometer, do use it andadd that information in!If you haven’t, not to worry.Having put your pictures into the tableRecord the weather you had in themiddle column