1. Chapter 5: Cloud Development and Precipitation
Atmospheric Stability
Determining stability
Cloud development and stability
Precipitation processes
Precipitation types
Measuring precipitation

2. Atmospheric Stability

3. Atmospheric Stability
stable and unstable equilibria
air parcels
adiabatic process
adiabatic lapse rates
Stability does not control whether air will rise or sink. Rather, it controls whether rising air will continue to rise or whether sinking air will continue to sink.

4. Determining Stability

5. A Stable Atmosphere environmental lapse rate absolute stability
stabilizing processes
subsidence inversions
Stable air provides excellent conditions for high pollution levels.

6. An Unstable Atmosphere
absolute instability
warming of surface air
destabilizing processes
superadiabatic lapse rates
Unstable air tends to be well-mixed.

7. Conditionally Unstable Air
conditional instability
dry and moist adiabatic lapse rates

8. Cloud Development and Stability

9. Cloud Development and Stability
surface heating and free convection
uplift along topography
widespread ascent
lifting along weather fronts

10. Convection and Clouds thermals fair weather cumulus
Fair weather cumulus provide a visual marker of thermals.
Bases of fair-weather cumulus clouds marks the lifting condensation level, the level at which rising air first becomes saturated.

11. Topography and Clouds orographic uplift rain shadow
The rain shadow works for snow too. Due to frequent westerly winds, the western slope of the Rocky Mountains receives much more precipitation than the eastern slope.

12. Precipitation Processes

13. Collision and Coalescence Process
terminal velocity
coalescence
warm clouds
A typical cloud droplet falls at a rate of 1 centimeter per second. At this rate it would take 46 hours to fall one mile.

14. Figure 5. 9: Conditionally unstable atmosphere
Figure 5.9: Conditionally unstable atmosphere. The atmosphere is conditionally unstable when unsaturated, stable air is lifted to a level where it becomes saturated and warmer than the air surrounding it. If the atmosphere remains unstable, vertical developing cumulus clouds can build to great heights.
Watch this Active Figure on ThomsonNow website at
Stepped Art
Fig. 5-9, p. 116

15. Ice Crystal Process cold clouds supercooled water droplets
saturation vapor pressures over liquid water and ice
accretion
The upper portions of summer thunderstorms are cold clouds!

16. Figure 5. 22: The ice-crystal process
Figure 5.22: The ice-crystal process. The greater number of water vapor molecules around the liquid droplets causes water molecules to diffuse from the liquid drops toward the ice crystals. The ice crystals absorb the water vapor and grow larger, while the water droplets grow smaller.
Watch this Active Figure on ThomsonNow website at
Fig. 5-22, p. 124

17. Figure 5. 22: The ice-crystal process
Figure 5.22: The ice-crystal process. The greater number of water vapor molecules around the liquid droplets causes water molecules to diffuse from the liquid drops toward the ice crystals. The ice crystals absorb the water vapor and grow larger, while the water droplets grow smaller.
Watch this Active Figure on ThomsonNow website at
Stepped Art
Fig. 5-22, p. 124

18. Cloud Seeding and Precipitation
silver iodide
It is very difficult to determine whether a cloud seeding attempt is successful. How would you know whether the cloud would have resulted in precipitation if it hadn’t been seeded?

19. Precipitation in Clouds
accretion
ice crystal process

20. Precipitation Types

21. Rain rain drizzle virga shower
Virga is much more commonly observed in the western US, because the humid climate of the eastern US reduces the visibility.

22. Snow snow fallstreaks dendrite blizzard
Snowflake shape depends on both temperature and relative humidity.

23. Sleet and Freezing Rain
rime
Sleet makes a ‘tap tap’ sound when falling on glass.

24. Snow Grains and Snow Pellets
graupel

25. Hail updraft cycles accretion
A hailstone can be sliced open to reveal accretion rings, one for each updraft cycle.

26. Figure 5.35: Hailstones begin as embryos (usually ice particles) that remain suspended in the cloud by violent updrafts. When the updrafts are tilted, the ice particles are swept horizontally through the cloud, producing the optimal trajectory for hailstone growth. Along their path, the ice particles collide with supercooled liquid droplets, which freeze on contact. The ice particles eventually grow large enough and heavy enough to fall toward the ground as hailstones.
Watch this Active Figure on ThomsonNow website at
Stepped Art
Fig. 5-35, p. 134

27. Measuring Precipitation

28. Instruments standard rain gauge tipping bucket rain gauge
It is difficult to capture rain in a bucket when the wind is blowing strongly.

29. Doppler Radar and Precipitation

30. Figure 5. 39: A microwave pulse sent out from the radar transmitter
Figure 5.39: A microwave pulse sent out from the radar transmitter. The pulse strikes raindrops and a fraction of its energy is reflected back to the radar unit, where it is detected and displayed, as shown in Fig
Stepped Art
Fig. 5-39, p. 135