Static Stability and Cloud Development

# Static Stability and Cloud Development

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## Static Stability and Cloud Development

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1. Static Stability and Cloud Development

2. Cloud Formation • What is static stability? • It describes what would happen to an air parcel if it was forced upwards. • It could keep rising • It could return back to it’s original/starting height • How is air is cooled to the saturation point? • If atmosphere is stable: • If atmosphere is unstable: Generally through vertical lifting Flat-layered type clouds form (stratus) Cumulus-type clouds form (puffy clouds)

3. Stratus

4. Cumulus

5. Stability

6. Parcel rising and sinking in the atmosphere

7. Dry Adiabatic Processes • Air is unsaturated (RH is below 100%) • The rate at which the temperature decreases with increasing altitude: dry adiabatic lapse rate (DALR.) • In these conditions, air cools at 5 deg/1000 ft

8. Example Estimate the temperature at Mt. Hamilton from the San Jose temperature. Assume the air is dry. Altitude of San Jose: ________________ Altitude of Mt. Hamilton: _____________ Temperature at San Jose: _______________ Temperature at Mt. Hamilton _______________ ~ 200 ft 4200 ft 80 degrees 60 degrees

9. Moist Adiabatic Processes Consider lifting an air parcel. It will cool according to the DALR as long as it remains unsaturated. At some height, the parcel will cool enough so that the air will reach its saturation point.

10. Moist Adiabatic Processes • If we were to raise the air above this height, then the excess vapor would condense. • The parcel of air will now cool at a different rate than the DALR.

11. Moist Adiabatic Processes The moist adiabatic lapse rate varies in the atmosphere (not constant). A typical value may be ~3°F/1000 ft. This will always be less than the dry adiabatic lapse rate of 5°F/1000 ft * Air cools LESS quickly when moist because it is receiving latent energy from the condensation.

12. Example Calculate the temperature at Mt. Hamilton from the San Jose temperature now assuming the air is moist. Altitude of San Jose: ________________ Altitude of Mt. Hamilton: _____________ Temperature at San Jose: _______________ Temperature at Mt. Hamilton _______________ ~ 200 ft 4200 ft 80 degrees 68 degrees

13. Atmospheric Stability A stable atmosphere

14. Atmospheric Stability An unstable atmosphere

15. Conditionally unstable atmosphere

16. How does air get forced upward? • Topography • Surface heating/convection • Convergence of surface air • Lifting associated with weather fronts

17. Convection