Clouds and Precipitation

1. Clouds and Precipitation

2. Clouds • Visible masses of tiny water droplets or ice particles suspended in the atmosphere. • 3 variables must be present for clouds to form. • Water vapor: air must be saturated. • Cool temperatures: air must be cooled to the dew point. • Condensation nuclei: provides a surface for condensation to occur. • Ex. : dust, salt, smoke.

3. Cloud formation • As warm air rises and expands, it cools. • When air reaches a level where its temperature is lower than dew point, condensation occurs to form a cloud. • The level where condensation forms is called the condensation level. • The base of the cloud forms here

4. What causes air to rise? • Mountains(Orographic Lifting) - Air hits mountains and is forced up • If one side gets all rain, what happens to other?

5. What causes air to rise? • Frontal Wedging- cool air acts as barrier over which warmer, less dense air rises

6. What causes air to rise? • Convergence- as air of the same density collides since it cannot be forced down, so it is forced up • Localized Convection- unequal heating of the Earth causes differences in density

7. Stability • Rising moving air = Unstable Air • Warm air rises into cold air. • Non- moving air = Stable Air • Warm air above cold air • Called inversion

8. Cloud Types

9. Cloud Types • Clouds are classified on the basis of their form and height. • Form • Cirrus – “hair like”, high altitude, wispy • Cumulus – “pile/pillow”, rounded • Stratus – “ layer”, sheets or layered, no distinction between individual clouds

10. Cloud Types • Height • High Clouds- Cirrus, Cirrostratus, Cirrocumulus • What do you notice? • Middle Clouds- Altostratus, altocumulus • What do you notice? • Low Clouds- Stratus, stratocumulus, nimbostratus, nimbus = “rainy cloud” • ????????????????????

11. High Clouds Cirrus Cirrostratus Cirrocumulus

12. Middle Clouds Altocumulus Altostratus

13. Low Clouds Stratus Stratocumulus Nimbostratus

14. Vertical Clouds • Some clouds do not fit into one layer, these cloud can build to towering heights. • Cumulus – puffy cloud usually found at low cloud levels • Cumulonimbus- formed from rising of unstable air • Often associated with thunder, lightning, and hail

15. Cumulonimbus

16. Mammatus Cloud – Occasionally found with cumulonimbus clouds

17. 3 4 5 12 2 6 7 1 8 9 10 11

18. Fog • Fog – a cloud at the surface of the Earth

19. Precipitation • Any moisture that falls from the air to the earth’s surface.

20. How rain forms • Collision-Coalescence • Step 1: Large water drop falls • Step 2: More drops are added • Step 3: Splat

21. Types of Precipitation • What kind of precipitation you receive depends upon if the water that falls freezes or melts during descent. • Drizzle: smaller water droplets • Rain: water is melted when it hits ground • Snow: water is frozen and stays frozen • Sleet: water freezes in mid-fall • Freezing Rain(glaze): water freezes upon impact • Hail: water is frozen as pellets and pellets grow in clouds.

22. Cloud Seeding • Method used to cause or increase precipitation. • Achieved by adding condensation nuclei to clouds