Chapter 2 (2.1) – Measuring Chapter 2 (2.1) – Measuring Weather DataWeather Data

Weather InstrumentsWeather Instruments

Science 10

ThermometersThermometers• 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

BarometersBarometers• 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.

BarometersBarometers• 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

Psychrometers Psychrometers

• 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

•

Partial Relative Humidity Chart for 30° C

Difference BetweenDry Bulb and Wet BulbTemperatures

Relative Humidity

None 100%

0.5° 96%

1.0° 93%

1.5° 89%

9.0° 44%

9.5° 42%

14.5° 19%

15.0° 17%

18.0° 5%

Psychrometers 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

Humidex Humidex • takes into account both temperature and relative humidity• Indicates how warm a given temperature will ‘feel’

See Figure 2.11, page

51

Anemometer & Wind Anemometer & Wind VaneVane

• 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

Beaufort Wind ScaleBeaufort Wind Scale• Measures wind speed without use of instruments• Uses qualitative observations to equate quantitative wind speeds

See Table 2.1, page 53

RadarRadar

• The Forecast Radar image shows where area of precipitation are expected to be.

• colors show the strength and physical phase of water

RadarRadarUses Doppler Effect

Weather BalloonWeather 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

Weather SatellitesWeather 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

Chapter 2 (2.2) – Chapter 2 (2.2) – Forecasting the WeatherForecasting the Weather

Science 10Science 10

Short- & Long-range Weather Short- & Long-range Weather ForecastsForecasts

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)

Weather Maps & SymbolsWeather Maps & Symbols

See Table 2.2, page 63

Analyzing Weather Maps for Analyzing Weather Maps for Short-Range ForecastingShort-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

Short-Range vs. Long-Range Short-Range vs. Long-Range ForecastingForecasting

• 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

Recall: Fronts and Recall: Fronts and their symbolstheir symbols

Fronts:Fronts:• Boundary between two air masses• Characterized by shift in weather

Cold Warm Stationary Occluded

5 Characteristics of 5 Characteristics of a Fronta Front

• Sharp temperature changes over a relatively short distance.

• Changes in air moisture content• Shifts in wind direction• Pressure changes• Clouds and precipitation

Cold FrontsCold Fronts

• Temperature – drops rapidly• Pressure – rises steadily• Clouds – Vertical building• Precipitation – Heavy along front• Winds – Strong and shifting

• Typically move faster than warm front

In the summer, cold In the summer, cold fronts can trigger:fronts can trigger:

• thunderstorms• large hail• dangerous winds• tornadoes

Warm FrontsWarm 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

Effects of warm Effects of warm frontsfronts

• 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

Stationary FrontsStationary Fronts

• Temperature – stagnent• Pressure – slightly fluctuates• Clouds – altocumulus• Precipitation – none• Winds – variable and light

• Can last for days weeks

Occluded FrontsOccluded 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

Pressure and Air Pressure and Air MovementMovement

Pressure Gradient Pressure Gradient ForceForce

• Difference in pressure over a given distance---between isobars Close together = step pressure gradient

STRONG winds Far apart = gentle pressure gradient

Light winds

• Just like contour lines

Pressure Gradient Pressure Gradient ForceForce

Winds Winds

•Horizontal movements at surface

•Names from WHEREWHERE it came from…not where it is going!!!

Around Pressure Around Pressure CellsCells