WEATHER & THE ATMOSPHERE

1. WEATHER & THE ATMOSPHERE

2. Weather Instruments • Used to measure the 5 major parts of weather observation 1. Atmospheric pressure 2. Humidity 3. Precipitation 4. Wind 5. Temperature

3. Tools: Atmospheric Pressure • Barometer: • Measures air pressure, millibars or inches of mercury

4. Tools: Humidity • Hair Hygrometer: • Uses hair to measure humidity, hair expands and contracts in response to water vapor content in the air. • (Sling) Psychrometer: • Difference between wet bulb and dry bulb used to determine relative humidity.

5. Tools: Precipitation • Rain Gauge: • Simple funnel with marks

6. Tools: Wind • Anemometer – Wind Speed • km per hour • mi per hour • Wind Vane – Wind Direction • Cardinal units or numerical

7. Measuring Upper-Atmospheric Conditions • Radiosonde: • Carried aloft by a helium balloon. • Measures upper-atmospheric. conditions: Relative humidity, air pressure, air temperature. • Information sent back to scientists via radio… waves.

8. Not weather satellites, but still cool Satellites • Carry cameras • Upper level Cloud speed, direct. • Hurricane observation • Infrared reading of cloud tops

9. The study of weather = METEROLOGY • Weather is the condition of the atmosphere at any given time or place • Much of weather forecasting and prediction can be accomplished by direct observation • To predict weather, you must make observations of the clouds, wind, temperature, humidity, air pressure and precipitation

10. ATMOSPHERIC VARIABLES • things that can be measured and change from moment to moment • Temperature • Air Pressure • Wind Speed and Direction • Water Content & Humidity • Cloud Cover • Precipitation • Others (dust, transparency, pollen, etc)

11. TEMPERATURE • Measures the average kinetic energy of molecules. • Heat enters the atmosphere from the sun as solar radiation (Insolation) • is an average of all of the kinetic energies- hence Average Kinetic Energy

12. 3 ways to Measure temperature: • Fahrenheit • Water freezes at 32° • Water boils at 212° • Celsius • AKA Centigrade (100 levels) • Water freezes at 0° • Water boils at 100° • Makes more sense and is easier to make a thermometer • Kelvin • Same scale as Celsius but 0 means zero energy • No degrees mark for Kelvin • 0K means that all atomic vibrations stop.

14. Air Pressure • the weight of the air in a certain area • Sinking air pushes down more- • cold air is dense air and brings high pressure • Hot air is less dense air and brings low pressure • Air pressure is measured using an instrument called a barometer • It is measured in inches (height of the mercury column in the barometer), or with the metric units called millibars

15. Air pressure drops with increasing altitude (less air) • Weather maps show sea level air pressure • It ranges from960mb – 1050mb

16. Air in the Atmosphere Relationships

18. Changes in Air Pressure • Temperature- warm air is lighter than cold air! • Humidity- humid (moist) air is lighter than dry air!! Water vapor (H2O) weighs less than the N and O gases that it pushed out • Winds are caused by the unequal heating of the atmosphere (remember that temperature causes changes in air pressure)

19. Water Vapor in the Air • The amount of water vapor in the air depends on the air temperature • The warmer the air, the more water vapor it can hold (think of those hot, humid summer days)

20. Relative Humidity • the amount of water vapor in the air, compared to how much water vapor it could hold at that temperature • Relative humidity is a percent measurement • Air with 100% humidity is said to be saturated • Precipitation will occur

22. Finding Relative Humidity • use an instrument called a hygrometer • One particular type of hygrometer is called a sling psychrometer • This instrument is made of two thermometers attached two a handle • One thermometer has a piece of gauze which is the soaked with water - This is called the WET BULB • The other thermometer is called the DRY BULB • These thermometers are swung in the air for a few minutes, and then the temperatures are recorded (take the wet bulb temperature first) • The wet bulb thermometer should have a lower temperature, since it removes heat from the thermometer as water evaporates from it

23. Interactive Site - http://www.eram.k12.ny.us/education/sctemp/12345/1269020014/rhdp.swf

24. Condensation and Dew • remember that air’s ability to hold moisture decreases as the temperature decreases • As the air cools, its relative humidity increases • When the relative humidity reaches 100% (saturated), the water comes out of the air as liquid droplets • The temperature at which this will occur is called thedew point

25. Condensation and Dew • Condensation can only occur if the water has something to condense on • Tiny particles in the air on which water condenses is called condensation nuclei • This can be dust, salts, chemicals from burning fuel, etc. • * Water vapor that condenses on the ground is called dew (think of walking across wet grass in the morning) • If the dew freezes on the ground, it is called frost • Water vapor condensing in the air forms clouds • If the cloud forms close to the ground, it is called fog