1. Do Now: Air rises ___________ and ____________ Air rises ___________ and ____________ Air sinks ___________ and ____________ Air sinks ___________ and ____________ Draw this picture and show what happens to air and show where clouds would form: waterland Mountain

2. Atmospheric Moisture

3. Moisture Exists in solid, liquid, and gas in atmosphere Exists in solid, liquid, and gas in atmosphere Water enters the atmosphere by: Water enters the atmosphere by: –Evaporation – liquid changes into gas –Transpiration – plants release water vapor –Evapotranspiration – evaporation + transpiration together Remember it ’ s the Sun that provides the energy for these to occur Remember it ’ s the Sun that provides the energy for these to occur

4. Factors affecting Evaporation: amount of energy available (more = faster evaporation) amount of energy available (more = faster evaporation) surface area of the water (spread out = faster evaporation) surface area of the water (spread out = faster evaporation) degree of saturation (more saturated = slower evaporation) degree of saturation (more saturated = slower evaporation) wind speed greater wind speed = greater evaporation) wind speed greater wind speed = greater evaporation)

5. Humidity Absolute Humidity - water vapor in each unit volume of air (or moisture capacity) Absolute Humidity - water vapor in each unit volume of air (or moisture capacity) - hotter air can hold more water vapor than cold air Relative humidity – ratio of the amount of water vapor in the air to maximum amount it can hold Relative humidity – ratio of the amount of water vapor in the air to maximum amount it can hold –The one you see in forecasts

6. Which is heavier? Which is heavier dry air or wet air? Which is heavier dry air or wet air? N2N2 O2O2 vs. N2N2 N2N2 O2O2 H2OH2O H2OH2O O2O2 Would a baseball travel further on a night where the air is saturated or dry?

7. Dew Point Dew point – temperature at which air is saturated (filled with water) Dew point – temperature at which air is saturated (filled with water) If air temp = dew point relative humidity = 100% If air temp = dew point relative humidity = 100% If air temp drops below dew point: water vapor condenses to liquid water If air temp drops below dew point: water vapor condenses to liquid water

8. Measuring Moisture Sling Psychrometer – instrument used to measure relative humidity and dew point Sling Psychrometer – instrument used to measure relative humidity and dew point –Dry bulb temp – ordinary thermometer –Wet bulb temp – thermometer with wet wick around it

9. To convert relative humidity and dew point You must use page 12 of ref. table You must use page 12 of ref. table 1. Subtract: dry bulb temp – wet bulb 2. Locate dry bulb on left side 3. Locate answer to step 1 on top of chart 4. See where those two numbers meet ****Make sure you are using the correct chart: dew point or relative humidity

10. Try a couple examples: 1. What is the relative humidity where the dry bulb temperature is equal to 18 o C and a wet bulb temperature of 15 o C? 2. What is the dew point temperature when dry bulb temperature is equal to -4 o C and a wet bulb temperature of -5 o C?

11. Cloud Formation 1. Air rises and cools 2. Air reaches dew point 3. Water begins to condense (gas -> liquid) 4. Water droplets form on condensation nuclei (dust particles / aerosols)

12. Air Masses

13. Air masses Air Masses – large body of air in the troposphere with similar characteristics (pressure, moisture, temp.) Air Masses – large body of air in the troposphere with similar characteristics (pressure, moisture, temp.) Form when air remains stationary over an area Form when air remains stationary over an area Where an air mass originates determines its characteristics Where an air mass originates determines its characteristics

15. Different Characteristics Continental (formed over land) = dry Continental (formed over land) = dry Maritime (formed over water)= wet Maritime (formed over water)= wet Polar or arctic = cold Polar or arctic = cold Tropical = warm Tropical = warm

16. Symbols on reference table p. 13 cP = continental polar = dry and cold cP = continental polar = dry and cold cT = continental tropical = dry and warm cT = continental tropical = dry and warm mP = maritime polar = wet and cold mP = maritime polar = wet and cold mT = maritime tropical = wet and warm mT = maritime tropical = wet and warm

17. Atmospheric pressure and density Air pressure and density are directly related. The denser the atmosphere, the greater the weight of a given volume of air. Air pressure and density are directly related. The denser the atmosphere, the greater the weight of a given volume of air. Atmospheric pressure aka barometric pressure- is the pressure due to the weight of the overlying atmosphere pushing down on any given area. Atmospheric pressure aka barometric pressure- is the pressure due to the weight of the overlying atmosphere pushing down on any given area.

18. Measurement of and changes in air pressure Barometers- used to measure air pressure. Barometers- used to measure air pressure. –2 types: mercury and aneroid. Mercury barometer is standard. –Barometric pressure in millibars can be converted to inches of mercury using the pressure chart in the ESRT. P.13 –The barometric trend (shown on weather maps) is how the magnitude of air pressure has changed over the past 3 hours.

19. Effect of temperature on air pressure As the temperature of air increases, the air expands and its density and pressure decrease. As the temperature of air increases, the air expands and its density and pressure decrease. Decreasing temperature has the reverse effect. Decreasing temperature has the reverse effect.

20. Effect of water vapor on air pressure The greater amount of water vapor in the air, the lower the air density and pressure. The greater amount of water vapor in the air, the lower the air density and pressure.

21. Effect of altitude on atmospheric pressure As altitude or elevation increases, atmospheric density and pressure decrease. As altitude or elevation increases, atmospheric density and pressure decrease. As you go up higher in the atmosphere, the less gas there is above you. As you go up higher in the atmosphere, the less gas there is above you.