Chapter 2 (2.1) – Measuring Weather Data Weather Instruments

1. Chapter 2 (2.1) – Measuring Weather DataWeather Instruments Science 10

2. Thermometers • Measure temperature or ‘average movement energy’ of particles in substance • Types: • Bulb Type • Bulb thermometers rely on the simple principle that a liquid changes its volume relative to its temperature • Thermresistor • Most common used today • This device changes its resistance of an electric current passing in it with changes in temperature

3. Barometers • measures atmospheric pressure in inches of mercury or millibars • 1 Bar = 1000 mB • Changes in pressure can forecast short term changes in the weather. • Barographs record long-term changes to identify Low and High pressure system.

4. Barometers • Mercury (Hg) type: • As atmospheric pressure increases, it pushes down on Hg in a tube • Gauge in tube measures change in pressure • Aneroid type: • Uses flexible container or aneroid cell that contains air • Lower pressure compresses air less than higher pressure • Changes in pressure measured as needle moves on scale • Changes in electrical resistance due to pressure changes can also be measured in electronic sensors

5. Psychrometers Partial Relative Humidity Chart for 30° C • Sling psychrometer • consists of two thermometers mounted together with a handle attached on a chain • One thermometer is ordinary (dry). The other has a cloth wick over its bulb and is called a wet-bulb thermometer • Any humidity in wet thermometer causes temp. difference between it and dry thermometer  can determine relative humidity

6. Psychrometers • Analog psychrometer • Uses natural or synthetic hair • In humid air, hair absorbs moisture causing it to extend • As humidity decreases, hair shortens • Differences in hair length can be measured and relative humidity determined • One thermometer is ordinary (dry). The other has a cloth wick over its bulb and is called a wet-bulb thermometer • Any humidity in wet thermometer causes temp. difference between it and dry thermometer  can determine relative humidity • Digital psychrometer • Moisture forms on silicon chip which conducts electricity and detect by sensor which determines humidity

7. Humidex • takes into account both temperature and relative humidity • Indicates how warm a given temperature will ‘feel’ See Figure 2.11, page 51

9. Anemometer & Wind Vane • includes both wind speed and wind direction sensors. • stands up to hurricane-force winds, yet are sensitive to the lightest breeze. • Wind direction vane identifies the direction of the wind

10. Beaufort Wind Scale • Measures wind speed without use of instruments • Uses qualitative observations to equate quantitative wind speeds See Table 2.1, page 53

12. Radar • The Forecast Radar image shows where area of precipitation are expected to be. • colors show the strength and physical phase of water

13. Radar Uses Doppler Effect

14. Weather Balloon • Contains a radiosonde device that measures weather conditions (i.e. temp., pressure, humidity) and transmits info electronically to receiver • Balloons can be tracked to determine wind speed and direction

15. Weather Satellites • Satellite images can show: • Cloud cover • H/L pressure systems • Movement of systems • Can detect IR radiation from Earth’s surface that has been reflected or scattered by precipitation • GOES & POES type satellites used

16. Chapter 2 (2.2) – Forecasting the Weather Science 10

17. Short- & Long-range Weather Forecasts Short-range a forecast that predicts how weather conditions will change over a period of up to 48 hours Long-range a forecast that predicts how weather conditions will change over a period of 3 to 7 days -relies on weather maps and remote sensing technology (i.e. weather balloons, radar, satellites)

18. Weather Maps & Symbols See Table 2.2, page 63

19. Analyzing Weather Maps for Short-Range Forecasting • Consider the following maps features: • Location of fronts • Speed & direction of fronts • Location of pressure systems (H & L) • Isobars – lines showing locations of same pressure • Isotherms – lines showing locations of same temperature

20. Short-Range vs. Long-Range Forecasting • Short-range forecasting is more accurate • Due to unpredictability of weather systems over time, computer modelling is used for long-range • Computer models have issues with local terrain and wind patterns

21. Recall: Fronts and their symbols

22. Fronts: • Boundary between two air masses • Characterized by shift in weather • Cold • Warm • Stationary • Occluded

23. 5 Characteristics of a Front • Sharp temperature changes over a relatively short distance. • Changes in air moisture content • Shifts in wind direction • Pressure changes • Clouds and precipitation

24. Cold Fronts • Temperature – drops rapidly • Pressure – rises steadily • Clouds – Vertical building • Precipitation – Heavy along front • Winds – Strong and shifting • Typically move faster than warm front

25. In the summer, cold fronts can trigger: • thunderstorms • large hail • dangerous winds • tornadoes

26. Warm Fronts • Temperature – rises slowly • Pressure – slight rise, then fall • Clouds – strato- and cirro- • Precipitation – long, steady • Winds – variable and light • Typically will have affect for days

27. Effects of warm fronts • Slow-moving warm front can mean days of wet weather before warm air • Sometimes water vapor in warm fronts condense to produce • rain • snow • sleet • freezing rain

28. Stationary Fronts • Temperature – stagnent • Pressure – slightly fluctuates • Clouds – altocumulus • Precipitation – none • Winds – variable and light • Can last for days weeks

29. Occluded Fronts • Temperature – • Warm – gets milder • Cold – gets colder • Pressure – • Warm - slight drop • Cold – slight rise • Clouds – cumulus • Precipitation – steady and light • Winds – variable and light

30. Pressure and Air Movement

31. Pressure Gradient Force • Difference in pressure over a given distance---between isobars • Close together = step pressure gradient • STRONGwinds • Far apart = gentle pressure gradient • Light winds • Just like contour lines

32. Pressure Gradient Force

33. Winds • Horizontal movements at surface • Names from WHERE it came from…not where it is going!!!

34. Around Pressure Cells