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Describing Weather Ch. 13, Lesson 1

Describing Weather Ch. 13, Lesson 1. What is weather?. Definition: The atmospheric conditions, along with short-term changes, of a certain place at a certain time Variables used to describe it: Air Temperature Air pressure Wind speed & direction Humidity Cloud coverage Precipitation.

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Describing Weather Ch. 13, Lesson 1

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  1. Describing Weather Ch. 13, Lesson 1

  2. What is weather? • Definition: The atmospheric conditions, along with short-term changes, of a certain place at a certain time • Variables used to describe it: • Air Temperature • Air pressure • Wind speed & direction • Humidity • Cloud coverage • Precipitation

  3. What is a meteorologist? • It is a scientist that studies and predicts weather • Which of the variables does this meteorologist discuss? • https://www.youtube.com/watch?v=oTwNvfbxEPI

  4. What is air temperature? • Definition: The measure of the average kinetic energy of molecules in the air • What does this mean? • Kinetic – means “motion” • Kinetic energy –”the amount of energy something has because of how much it is moving”. • Kinetic energy of molecules – “how much energy molecules have because of how much they are moving.”

  5. Speed of molecules-kinetic energy Low Temperatures = Low Kinetic Energy High Temperatures = High Kinetic Energy

  6. Thermometers are Speedometers • When a thermometer is used to measure temperature, it is actually measuring how fast the molecules around it are moving

  7. Low temperature- slow moving High Temperature – fast moving molecules produce little kinetic molecules produce lots of kinetic energy and thermometer registers energy and thermometer that low energy as low temperature registers high energy as high temperature

  8. Temperature can vary due to: • Time of Day • Season • Location • altitude

  9. What is air pressure? Definition: the force that a column of air applies on the air or a surface below it Less air pressure at top of atmosphere; more pressure lower in the atmosphere

  10. How do we measure air pressure? • A barometer measures air pressure • Because of the name of the instrument that measures it, air pressure is also referred to as “barometric pressure” • It’s measured in “millibars.” • https://www.youtube.com/watch?v=GRxglLS1YWI

  11. (One more time…)What Causes Wind? • Wind blows from areas of high pressure to areas of low pressure • Wind direction is the direction FROM WHICH the wind is blowing. • Ex: Westerly winds blow FROM THE WEST to the East • Wind speed is measured by an anemometer

  12. What is humidity and relative humidity? Humidity RELATIVE HUMIDITY Definition: the amount of water vapor in the air compared to the amount of water vapor the air could contain AT THAT TEMPERATURE Measured in: a percentage by a psychrometer For example: air that contains only half the water vapor that it could hold has a relative humidity of 50% • Definition: the amount of water vapor in the air • Measured in: grams of water per cubic meter of air • That means the weight of water that is contained in a certain volume of air

  13. What type of air can contain the MOST water vapor? • Warm air can contain more water vapor than cold air.

  14. What happens when the air reaches a level of 100% • Air that contains as much water vapor as it can possibly hold is said to be saturated (Think of a sponge that is full of water and can’t hold any more.) • Just like a saturated sponge that begins to drip, saturated air also begins to “drip”. In other words, the water vapor also begins to come out of the air and form water.

  15. 2 Things can happen to saturated air Air near ground Higher in the atmosphere _____________ form. • If temperature is above 32 degrees, ____________ forms. • If temperature is below 32 degrees, __________ forms.

  16. Dewpoint • Definition: The temperature at which air is saturated and condensation can occur • When the temperature decreases, air can hold ____________ moisture? • LESS!

  17. What will we do tomorrow in lab? • https://www.youtube.com/watch?v=jmQ8FWnM0fA

  18. Let’s talk about clouds

  19. How do clouds form?

  20. How clouds form – part 2 Particles such as dust, salt or smoke

  21. Clouds are classified by: • Shape • Altitude in which they form

  22. Examples of clouds: • Stratus – flat, white, layered • Up to 2,000 meters high • Cumulus – fluffy, heaped or piled up • From 2,000-6,ooo meters high • Cirrus – wispy • Above 6,000 meters high

  23. What is Fog? • Fog is a cloud that is formed near Earth’s surface • It is a suspension of water droplets or ice crystals close to or at Earth’s surface • It reduces visibility (the distance a person can see into the atmosphere)

  24. Let’s look at some forms of precipitation • Look at Figure 5 on page 455 • Describe the difference between rain, snow, sleet and hail.

  25. The Water Cycle Key Concept check, page 455 Answer: Water evaporates into the atmosphere when the air temperature is warm, and it falls back to Earth when the temperature cools enough to cause condensation and precipitation.

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