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- 2. Clouds ENVSN Humidity is a percentage. It is the ratio between the quantity of water vapor contained in the air and the maximum amount it can contain. 40% = dry air 80% = moist air 100%= saturated air Humidity
- 3. Clouds ENVSN Hot air can contain more water vapor than cold air. When temperature rises, droplets suspended in the air are changed into water vapor. Cold air can contain less water vapor than hot air. When temperature decreases, air cools until become saturated. Then any additionnal cooling causes water vapor to condense And then to rain! (The dew point is the temperature where dew can form.) So form clouds! Clouds are the aggregate of fine water droplets or ice particles suspended in the air. They form by water vapor condensation when moist air cools Humidity
- 5. Clouds ENVSN How to recognise clouds? Clouds have several features: color, size, thickness, density, shape, height, texture, transparency… However, we divided the basic clouds types according to 2 main criteria: - Their shapes - Their height Clouds
- 6. Clouds ENVSN The 2 main shapes of clouds Strato- form clouds – Wide spread, large horizontal extension – Little thick – Diffuse edges – Stability clouds Cumulo-form clouds - Look like cotton balls - Vertical extent from 10m to 12km (vertical motions are more or less important) - Sharp outlines - Unstability clouds
- 7. Clouds ENVSN Distinguish the shape of clouds: Strato-form or cumulo-form is a determining indication for my navigation. Strato- form clouds Regular wind Cumulo-form clouds Irregular wind, gusts Clouds
- 8. Clouds ENVSN The more the cumulo-form cloud has of a vertical extent (the thicker it is), the more the wind will be irregular.
- 9. Clouds ENVSN Then clouds are divided by the height of their bases: - High level clouds - Mid level clouds - Low level clouds The height gives the prefix in the name of a cloud (cirro-, alto-…) The shape gives the suffix in the name of a cloud (-cumulus or –stratus)
- 10. Clouds ENVSN What do these clouds look like?
- 11. Clouds ENVSN Here are the strato-form…
- 12. Clouds ENVSN The heigher of the strato-form: cirrostratus (Cs) • High, transparent, and whitish veil • Cover partially or totally the sky • Characteristic: Halo around the sun or the moon • Ice crystals • No precipitation
- 13. Clouds ENVSN Strato-form at mid level : les altostratus (As) • Greyish cloud sheets • Cover partially or totally the sky • Characteristic: Reveal the sun as if seen through ground glass • Water droplets, ice crystals or snow • Possible precipitation: rain, snow, hail
- 14. Clouds ENVSN Strato-form at low level : : stratus (St) • Uniform gray cloud layer • Fog, mist • Water droplets, possibly ice crystals • Possible precipitation: drizzle, eventualy snow
- 16. Clouds ENVSN The higher of the cumulo-form: cirrocumulus (Cc) • High small elements in the form of more or less regularly arranged grains • Apparent width of one element <1° (~width of one finger at arm’s length) • Ice crystals • No precipitation
- 17. Clouds ENVSN Cumulo-form at mid-level: altocumulus (Ac) • White or grey layered clouds composed of regularly arranged elements • Apparent width of one element: 1 to 5° (~width of three fingers at arm’s lenght) • Water droplets, sometimes ice crystals
- 18. Clouds ENVSN The cumulo-form at low level: cumulus (Cu) • Look like balls of cotton wool • Detached clouds, sharp outlines, cauliflower form • More or less important vertical extent (until 12km for Cb) • The more important the vertical extent is, the more the atmosphere is unstable • Water droplets and ice crystals for the thickest • Possible precipitation when they are thick: rain, snow, hail • More or less gusty
- 19. Clouds ENVSN • Cumulonimbus (Cb) Maximal vertical extent (14km). Anvil. Rain, snow, hail, and thunderstorm are possible. Gusts • Cu congestus Strong vertical extent. Rain, snow and gusts are possible • Cu humilis Little vertical extent Nice weather, no precipitation Becareful! Big cumulus, congestus cumulus and especially cumulonimbus may create big squalls: showers + irregular and violent winds! => It is essentiel to spot them and to anticipate them Clouds
- 20. Clouds ENVSN 1.Strato- form or Cumulo-form? What do you think? (Answer slide 25)
- 21. Clouds ENVSN 2. Strato- form or Cumulo-form? What do you think? (Answer slide 25)
- 22. Clouds ENVSN 3. How high? Which cloud ? What do you think? (Answer slide 25)
- 23. Clouds ENVSN 4. Which cloud? What do you think? (Answer slide 25)
- 24. Clouds ENVSN 5. How high? Which cloud ? What do you think? (Answer slide 25)
- 25. Clouds ENVSN Answers: 1. Strato-form 2. Cumulo-form (cumulus and cumulonimbus) 3. High, Cirrus 4. Cirrostratus 5. Middle. Altocumulus
- 26. Clouds ENVSN Are there other types of clouds?
- 27. Clouds ENVSN Cirrus (Ci) • High-level clouds • White delicate filaments, hair- like • Ice crystals • No precipitation When cirrus clouds invade the sky, a Low approaches! Clouds
- 28. Clouds ENVSN Nimbostratus (Ns) • The only strato-form with vertical extent • Low and middle levels • Dark grey cloud layer • Diffuse edges • Almost always precipitation: strong rain, snow or hail Becareful! Nimbostratus create big showers and more or less gusty winds! Clouds
- 29. Clouds ENVSN Stratocumulus (Sc) • Grey or whitish patch or layered clouds • Between strato-form and cumulo- form • Possible precipitation: rain or light snow
- 31. Clouds ENVSN 1. Take a picture of the sky. Share it on the Facebook group: https://www.facebook.com/groups/meteo.envsn/ And give the name of the clouds you observe. 2. Comment the picture of your colleagues