Weather Factors page 51

Weather Factors

Recall that Weather is defined as the state of atmosphere at a specific time and place and that most weather occurs in the troposphere.

Wind, clouds, and precipitation are all the result of the atmosphere responding to uneven heating of the Earth by the Sun.

The uneven heating causes temperature differences, which in turn causes wind, which then moves the heat to a new place.

The atmosphere thus becomes a giant "heat engine", continuously driven by the sun.

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What causes weather?• Caused by the transfer of energy between

these 3 things:- The Sun, Earth’s surface, and the Atmosphere.

• Caused by the transfer of energy between these 3 things:- The Sun, Earth’s surface, and the Atmosphere.

Hot air rises and cools

The sun warms earth’s surface - increasing its temperature.

Water vapor condenses to form clouds & precipitation

The sun’s energy is used to evaporate water and put moisture into the air.

Unequal heating and differences in air pressure cause wind.

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Is - the branch of science dealing with weather forecasting.

Atmospheric conditions that are typically measured to provide information for weather forecasts and to study the weather and climate include: temperaturebarometric pressurehumiditywind speed & directionprecipitation

Condition: Partly Cloudy

Humidex: 30 o CPressure: 101.4 kPa

Mr. Fetch’s Earth Science Classroom

Temperature – a measurement of heat Temperature is a factor of particle motion.

Faster moving particles create more heat

Temperature is measured with a thermometer

Factors affecting the temperature of an area include such things as

locationamount of sunshineseason weather and pressure systems

Mr. Fetch’s Earth Science Classroom

Examples of Factors that affect temperature

Cities are WarmerCities are Warmer Mountains are ColderMountains are Colder

Cloudy daysCloudy daysare Coolerare Cooler

Cloudy nightsCloudy nightsare Warmerare Warmer

Mr. Fetch’s Earth Science Classroom

Wind

Wind is moving air

It is caused by differences in air pressure within the atmosphere.

Air under high pressure moves toward areas of low pressure

Wind Direction is measured with a weather vane or wind sock

Blunt end of arrow is where the wind is coming fromPointy end of arrow is where the wind is blowing to

Sketch a picture of these two devices

What is the wind direction shown?

Answer: Wind is blowing FROM the SW

Wind direction is reported by the direction from which it originates

Wind Speed is measured with an Anemometer

An anemometer is an instrument with three or four small metal cups that catch the wind. An electrical device records the revolutions of the cups and calculates the wind speed (km/hr)

Mr. Fetch’s Earth Science Classroom

Barometric Pressure

Atmospheric/air pressure is measured with a barometer in units of inches of mercury or millibars

Barometric pressure is the force exerted on objects by the weight of the atmosphere above them.

Mr. Fetch’s Earth Science Classroom

Precipitation: Change of State

MELTINGUses Heat

FREEZINGGives off Heat

Sublimation

Uses Heat

Deposition

Gives off Heat

Gives off Heat

Uses Heat

EVAPORATION

CONDENSATION

Freezing/Melting point of water/ice is 00C

+ Add energy

- Subtract energy

Amounts of precipitation are measured with a rain or snow gauge.

Relative HumidityRelative humidity is a

measure of the amount of water vapor in the air compared to the maximum amount of water vapor the air can hold at that temperature.

A psychrometer is one instrument that measures relative humidity.

Mr. Fetch’s Earth Science Classroom

Hot air holds more moisture than cold air.

Dew Point and HumidexThe dew point is the temperature which water

vapor in air will condense into liquid water. Condensed water is called dew when it forms on a solid surface (like grass) or a cloud when it forms in the sky.

The humidex (short for "humidity index") is a number used to describe how hot the weather feels to the average person. The humidex is a unit-less number based on the dew point, and is equivalent to the dry temperature in degrees Celsius.

Answer Questions on page 55

Answer key for page 551. 56 2. 41 3. 74.4 4. 94

5. a. N b. S6. a. SW b. NE7. a. N b. S

8.a. Melting + b. Condensation -c. Sublimation + d. Deposition -e. Freezing - f. Evaporation +

9. A. Time and Place B. Boiling (liquid to gas) C. Zero celcius D. Increasing by 1 degree E. Downtown/city that has cement to absorb more heat and pollution to trap it and keep it there F. Wind sock or weather vane G. Anemometer H. Barometer I. Sun, earth’s surface, atmosphere J. Higher K. Wind turns cups, cups spin, speed of wind calculated from speed of revolving cups