Chapter 5: Cloud development and precipitation

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 riseor 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 pollutionlevels

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 airfirst becomes saturated

11. Topography and clouds • orographic uplift • rain shadow • The rain shadow works for snow too. Due to frequentwesterly winds, the western slope of the Rocky Mountainsreceives 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. 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!

15. Cloud seeding and precipitation • cloud seeding • silver iodide • It is very difficult to determine whether a cloud seedingattempt is successful. How would you know whetherthe cloud would have resulted in precipitation if it hadn’tbeen seeded?

16. Precipitation in clouds • accretion • ice crystal process

17. Precipitation types

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

19. Snow • snow • fallstreaks • dendrite • blizzard • Snowflake shape depends on both temperature andrelative humidity

20. Sleet and freezing rain • sleet • freezing rain • rime • Sleet makes a ‘tap tap’ sound when falling on glass

21. Snow grains and snow pellets • snow grains • snow pellets • graupel

22. Hail • updraft cycles • accretion • a hailstone can be sliced open to reveal accretion rings,one for each updraft cycle

23. Measuring precipitation

24. Instruments • standard rain gauge • tipping bucket rain gauge • It is difficult to capture rain in a bucket when thewind is blowing strongly

25. Doppler radar and precipitation • radar • Doppler radar