Part 2. Water in the Atmosphere

1. Part 2. Water in the Atmosphere Chapter 6 Cloud Development and Forms

2. Introduction • Clouds form as parcels of air lift and cool • Clouds are instrumental to the Earth’s energy and moisture balances • Mechanisms that Lift Air • Orographic lifting • Frontal lifting • Convergence • Localized lifting

3. Leeward side is dry (rainshadow) Windward side is rainy Orographic uplift (right) and orographically induced clouds (below)

4. Frontal lifting • A front is a boundary between unlike air masses • Warm/moist air rises to form clouds • Cold(a)andwarm (b) fronts occur

5. Convergence • Air converging into low pressure regions • Localized convection • Free • Forced (mechanical)

6. Static Stability and the Environmental Lapse Rate (ELR) • Static stability= air’s susceptibility to uplift • The environmental lapse rate compared to the dry and moist adiabatic lapse rates determines the static stability of air • Types of static stability • Absolutely unstable air • Absolutely stable air • Conditionally stable air

7. Absolutely unstable air = dry adiabatic lapse rate is less than environmental lapse rate (positive bouyancy) (Box 6.1.1, ELR 1)

8. Absolutely unstable, unsaturated air Rising air parcel stays warmer than outside environmental air Absolutely unstable, saturated air (See Box 6.1.1 environmental lapse rate 1)

9. Absolutely stable air = moist adiabatic lapse rate is greater than the environmental lapse rate (negative bouyancy) (Box 6.1.1, ELR 3)

10. Absolutely stable, unsaturated air Rising air parcel stays colder than outside environmental air Absolutely stable, saturated air (See Box 6.1.1 environmental lapse rate 3)

11. Conditionally stable air = dry adiabatic lapse rate is greater than the environmental lapse rate, but the moist adiabatic lapse rate is less than the environmental lapse rate (Box 6.1.1, ELR 2)

12. Conditionally unstable situation, unsaturated air Rising dry air parcel stays cooler than outside environmental air (stable) Rising moist air parcel stays warmer than outside environmental air (unstable) Conditionally unstable situation, saturated air (See Box 6.1.1 environmental lapse rate 2)

13. Heating/cooling the lower atmosphere changes the ELR A diurnal profile of the ELR

14. Advection of Cold/Warm Air at Different Levels can change the ELR

15. Advection of an Air Mass with a Different ELR

16. Limitations on the Lifting of Unstable Air • Stable layers aloft will limit how high air can be lifted This stable layer is also called an inversion layer

17. Profile of a frontal inversion

18. Profile of a subsidence inversion

19. Cloud types are based on appearance and/or height

21. Cirrus with fall streaks Cirrus clouds are composed entirely of ice crystals

22. Altocumulus “Alto” level clouds are composed of both water droplets and ice crystals Stratus Low clouds are composed entirely of water droplets

23. Stratocumulus

24. Clouds with vertical development • Cumulus • Cumulus humilis, cumulus congestus, cumulonimbus Cumulus humilis

25. Cumulus congestus

26. Formation of fair weather cumulus

27. Cumulonimbus

28. Unusual clouds • Lenticular • Banner clouds • Mammatus • Nacreous clouds (mother of pearl) • Noctilucent clouds

29. Lenticular Banner cloud

30. Nacreous Noctilucent

32. = Visible image • = Infrared image • = Color-enhanced infrared