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.

m What causes weather? 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

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:  temperature  barometric pressure  humidity  wind speed & direction  precipitation

Condition: Partly Cloudy Humidex: 30 o C Pressure: 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  location  amount of sunshine  season  weather and pressure systems

Mr. Fetch’s Earth Science Classroom Examples of Factors that affect temperature Cities are Warmer Mountains are Colder Cloudy days are Cooler Cloudy nights are Warmer

Mr. Fetch’s Earth Science Classroom Wind Wind is moving air It is caused by differences in air pressure within the atmosphere.air pressureatmosphere 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 from Pointy 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 MELTING Uses Heat FREEZING Gives off Heat Sublimation Uses Heat Deposition Gives off Heat Uses Heat EVAPORATION CONDENSATION Freezing/Melting point of water/ice is 0 0 C + Add energy - Subtract energy

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

Relative Humidity Relative 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 Humidex The 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 a. N b. S 6. a. SW b. NE 7. 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