Textbook, chapter 4, p. 100-106

1. clouds Textbook, chapter 4, p. 100-106

2. Cloud classification • Originally by Luke Howard (1850’s) • Currently used nomeclature based on Abercromy & Hildebrandsson (1887) • Linnean system (genus, species) • morphological only, not genealogical • Latin Root Translation Example • cumulus heap fair weather cumulus • stratus layer altostratus • cirrus curl of hair cirrus • nimbus rain cumulonimbus

3. Cloud subclassification Further classification identifies clouds by height of cloud base. 3 levels Examples: the prefix "cirr-" (as in cirrus clouds) refers to high levels, the prefix "alto-" (as in altostratus) refers to middle levels.

4. Relative heights vary zonally H M L H M L H M L tropopause Tropics Midlatitudes Poles

5. Cloud types and relative altitudes

6. High clouds composed of ice crystals fibrous or filamentous shape ice crystal concentration generally very small

7. Cirrus uncinus (mares’ tails) Height (km): 7-10 km+ Falling light snow [fallstreaks], not reaching the ground. distorted by upper-tropospheric wind shear.

8. Cirrus Cirrus uncinus Cirrus floccus Cirrus fibratus vertibratus Cirrus uncinus

9. Cirrus Cirrus uncinus Cirrus spissatus Cirrus spissatus with virga

10. Cirrostratus continuous sun shines thru, no precipitation process: widespread ascent aloft, or old thunderstorm anvil halo

11. Cs broken into waves sun shine thru, no precipitation process: widespread ascent combined with convective overturning in a thin layer. Cirrocumulus

12. Middle clouds * occur at altitudes where temperatures range between 0 and -25ºC (32 and -13ºF). * composed of supercooled water droplets, or are in mixed-phase (supercooled water droplets and ice crystals). Altostratus clouds occur as uniformly gray or white layers that totally or partially cover the sky. They are usually so thick that the sun is only dimly visible, as if viewed through frosted glass.

13. Altostratus Height (km): base=2-6 km, can be thick, liquid or ice, no precipitation reaching the ground. Process: widespread stable ascent, often preceding a surface warm front. Altostratus has a uniform and diffuse coverage

14. Iridescent Altostratus (difraction)

15. Altocumulus base=2-6 km, usually thin, usually liquid, no precipitation. Process: widespread ascent combined with convective overturning aloft (left) or with wave activity (right) clear regions  descending air cloudy regions  ascending air

16. Altocumulus Sharp cloud boundaries indicate the presence of water droplets rather than ice crystals. Altocumulus castellanus Altocumulus stratiformis

17. Altocumulus lenticularis

18. Low-Level Clouds * usually at temperatures above -5ºC (23ºF) * composed mostly of water droplets. geostationary satellite precipitation

19. Stratus Base>0.1 km, top<3 km, liquid (or ice), may have drizzle falling. Process: stable ascent, mixing Fog occurs when stratus meets the ground; when it lifts, it may break up into stratocumulus.

21. Nimbostratus steady light precipitation

22. Stratocumulus Shallow, usually liquid, no precipitation Process: forced or spontaneous overturning in a shallow layer

23. Marine stratocumulus

24. cumulus Buoyantly rising air parcels (thermals) become saturated Cu cloud base … LCL Shallow or deep Cumulonimbus Cu mediocris Cu humulis LCL

25. Fair-Weather Cumulus Widely separated heap clouds of small vertical development. With flat bottoms and rounded tops, they resemble a flock of sheep grazing in a pasture.

26. Cu humilis or mediocris

27. Cumulus congestus Larger and deeper  cauliflower appearances to the tops. Base is flattish, representing the LCL. Can produce showers. Cloud top=5-7 km, above the freezing level but usually still liquid.

28. Cumulonimbus Look at this animation

30. 12 June 2004, Hastings NE. Photo by Doug Raflik

31. Cumulonimbus: the most active member of the cumulus family Convective family over the South China Sea

32. Cumulonimbus

33. A: cirrus B: cirrostratus C: cirrocumulus D: altostratus E: altocumulus F: stratus G: stratocumulus H: cumulus humilis I: cumulus congestus J: cumulonimbus J: nimbostratus Pop quizzes: cloud identification

34. cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus a mid-level cloud in the lee of mountain ranges

35. cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

36. cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

37. Hint: it is overcast, but not raining • cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

38. cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

39. cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

40. Hint: this cloud layer is low • cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

41. Hint: this cloud layer is high • cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

42. cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus this is a halo

43. Hint: it is raining • cirrus • cirrostratus • cirrocumulus • altostratus • altocumulus • stratus • stratocumulus • cumulus humilis • cumulus congestus • cumulonimbus • nimbostratus

45. A few other cloud visual clues1. anvil development view this animation process: buoyant ascent lightning usual (lightning is rare over the oceans) much precip evaporates if LCL is high

46. Cumulonimbus: Severe weather lightning, thunder, heavy rains, hail, strong winds, and tornadoes … Model simulations: Typical thunderstorm Severe thunderstorm

47. Cumulonimbus: Shelf clouds We are just ahead of a severe thunderstorm. Dewpoints are in the mid-70s. Winds gust to over 40 mph with the passage of this shelf cloud. Evaporatively cooled air is pushed out of the precipitation area by the downdraft, warm air slides up and over the gust front forming the concave-shaped shelf cloud.

48. Cumulonimbus: Mammatus clouds pockets of negatively-buoyant air, filled with snow suspended from the anvil base

49. Mesoscale Convective Complexes Radar animation

50. Orographic and wave clouds Orographic clouds are produced by the flow of air interacting with mountainous terrain. They often indicate areas of clear air turbulence. lee wave mountain wave