Weather elements unit 15

transcript

Unit 15: Weather Elements

Objectives

Differentiate between weather and climate.Understand the use and siting of the weather

instruments.

Weather

• Weather describes the condition of the atmosphere of a place over a short period of time.

• Temperature, rainfall and wind

Climate

• Climate is the average conditions of the atmosphere of a place over a long period of time.

• Average temperature and average rainfall pattern is used.

Is this weather or climate data?

Is this a weather or climate data?

Climatic maps are used to show information such as distribution of temperature and rainfall of a country, region or the world.

Thermometer

• Temperature refers to the degree of heat in the air. It tells us how hot or cold the air is.

• A thermometer is used to measure temperature in degree Celsius (◦C) or degree Fahrenheit(◦F).

• Six’s Thermometer or the maximum and minimum thermometer is used to record the highest and lowest temperatures of a day.

Six’s thermometer

• Made up of Mercury and Alcohol

• Mercury – Very high boiling point

• Alcohol – Very low freezing point

• Read off the base of the Indices (Indicators)

Activity - Reading the Six’s

Max = 30 oCMin = 5 oC

Mercury

Metal Indices

Alcohol

Max = 20 oCMin = 10 oC

Max = 7.5 oCMin = -15 oC

Stevenson Screen

• The Six’s thermometers are placed in a white, wooden box called a Stevenson Screen.

• White wooden box to reflect heat• Louvred sides to allow air to flow freely• Doubled layered roof to prevent direct heating

from the sun• Stand on stilts to prevent heat from the

ground to be trapped

Calculating Temperatures (1/5)

Daily temperature Range

= Maximum Temp - Minimum Temp

For exampleMax temp = 30 oC Min Temp = 10 oC

Daily temp range = 20 oC

Mean (average) daily temperature = Maximum Temp + Minimum Temp 2

For exampleMax temp = 30◦C Min Temp = 10◦C Average daily temp= (30+10)/2 = 20◦C

Mean (average) monthly temperature

= Total average daily temp for the month Number of days in the month

Calculating Temperatures (3/5)Mean (average) monthly temperature

= Average max temp + Average min temp 2

Only used this when average maximum and average minimum temperature are given.

Mean (average) Annual temperature

= Total average monthly temp in a year 12

Annual temperature range

= Highest mean - Lowest mean monthly temp monthly temp

Location XMonth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Temp 23 22 20.5 16.5 14 10.5 10 11 12.5 14 17.5 21

Mean Annual Temperature= Total of mean monthly temperature / 12= (23 + 22 + 20.5 + 16.5 + 14 + 10.5 + 10 + 11 + 12.5 + 14 + 17.5 + 21 ) / 12= (192.5) / 12

= 16.04 oC

Annual Temperature Range= Highest Temperature – Lowest Temperature= 23 – 10

= 13 oC

Location YMonth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Temp 25.5 26 26.5 27 27.5 28 27.5 27 26.5 26.5 26 26

Mean Annual Temperature= Total of mean monthly temperature / 12= (25.5 + 26 + 26.5 + 27 + 27.5 + 28 + 27.5 + 27 + 26.5 + 26.5 + 26 + 26 ) / 12= (321) / 12

= 26.75 oC

Annual Temperature Range= Highest Temperature – Lowest Temperature= 28 – 25.5

= 2.5 oC

• Average daily or mean daily temperature:

• Calculation of temperature data:

Temperature

Average daily ormean daily temperature

Maximum temperature + Minimum temperature2

Daily temperature range Maximum temperature - Minimum temperature

Average monthly temperature

Sum of average daily temperatures for the monthNumber of days in the month

Average annual temperature

Sum of average monthly temperatures in a year12

• Daily temperature range

• Average monthly temperature

• Average annual temperature

• An instrument used to measure the amount of rainfall

• Rain falls through a funnel and is collected in the bottle

• Excess rain that overflows is collected in the copper cylinder

• Amount of rain collected is poured into a measuring cylinder, calibrated in millimeters

• Rain gauge:

Rainfall

outer cylinder funnel glass bottle

measuring cylinder

copper cylinder

• One-third of the rain gauge is sunk into the ground to prevent toppling

• To be placed in an area free of obstructions

• Rain gauge:

Rainfall

copper cylinder

funnel

glass bottleouter cylinder

Calculating Rainfall (1/4)

Daily rainfall

= Sum of all rainfall readings in a day

Monthly rainfall

= Sum of all daily rainfall readings in a month

Total annual rainfall

= Sum of the total monthly rainfall received for the year.

Mean (average) monthly rainfall

= Total annual rainfall 12

• Horizontal movement of air from a high pressure area to a low pressure area

• Associated with land and sea breezes

windhigh

pressurelow pressure

cold air sinkswarm air rises

land Sea

Wind• In the day, air over the sea is cooler than that over the land, thus the cooler air sinks, creating a higher pressure area.

•Warmer air over the land rises, creating a low pressure.

•Differences in pressure cause the air over the sea to move towards the low pressure over the land.

•This horizontal movement of air causes wind.

NOTE: Greater differences in pressure give rise to stronger breezes.

•The wind vane points to the direction where the wind is blowing from

• It is made up of a freely moving pointer and four cardinal points – north, south, east, west

• Measuring wind direction:

Wind vane

•The wind rose records the wind direction.

• It is represented by a centre circle and eight arms representing the main eight compass directions.

•The number of calm days is recorded in the centre circle.

•The longer the arms, the more days the wind is received from that direction.

Wind rose

number of calm days5

• Siting of weather instruments:

Stevenson screen• 120cm above ground level• Six’s thermometer is kept inside• insulated from heat by material

and design

Stevenson screen• 120cm above ground level• Six’s thermometer is kept inside• insulated from heat by material

and design

rain gauge• 30cm above ground level• on short grass away in an open

field from buildings

rain gauge• 30cm above ground level• on short grass away in an open

field from buildings

wind vane• top of the meteorological

station with no obstructions

wind vane• top of the meteorological

station with no obstructions

5 meteorological/weather stations in Singapore

Weather elements unit 15

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