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

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 Tropics Midlatitudes Poles H M L tropopause

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 uncinus Cirrus floccus Cirrus uncinus Cirrus fibratus vertibratus Cirrus

9. Cirrus spissatus Cirrus spissatus with virga Cirrus uncinus

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

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

12. Middle clouds 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. * 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).

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

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 LCL  Cu humulis Cu mediocris Cumulonimbus

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

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

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

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

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

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

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

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

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

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

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

45. A few other cloud visual clues 1. anvil development process: buoyant ascent lightning usual (lightning is rare over the oceans) much precip evaporates if LCL is high view this animation

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. mountain wave lee wave

51. Altocumulus lenticularis

52. Lenticular clouds Altocumulus lenticularis are the "mountain-wave clouds." As strong horizontal winds encounter a mountain range, gravity waves propagate upwards, and leeward. Mountain waves are stationary.

53. Ac lenticularis elsewhere RH stratification may yield a ‘stack of pancakes’ Plymouth, NH, 3 Dec ‘96 Which one is liquid which one ice ?

54. Unusual AC lenticularis

55. Mountain-wave turbulence Föhn wall cloud, Rockies turbulent rotor cloud in Owens Valley, CA, downwind of the Sierras.

56. Mountain-wave turbulence : Banner clouds

57. Banner cloud or lenticular cloud ? (same mountain)

58. Kelvin-Helmholtz waves and KH billows KH waves form when strong wind shear overturns a stable layer (i.e., an inversion). They are usually invisible! (CAT)

59. Kevin-Helmholtz instability

60. Breaking billows – an aviation hazard

61.  Kelvin-Helmholtz waves on Jupiter. Colors indicate the clouds' altitudes: blue is lowest through red as highest.

62. Cap clouds Pileus, Latin for "skullcap," is a smooth cloud that forms when a stable, humid layer aloft forced to rise by a penetrating Thunderstorm cell.  cap cloud on a Cb Pileus cloud attached to the top of a cumuliform cloud.

63. “Morning glory” roll clouds These occur when a deep stable layer overruns a shallower stable layer. Gravity waves ahead of the deep layer result in roll clouds, and may cause severe turbulence. ~1000 km

64. Air rises and condenses at the leading edge, and evaporates behind

65. These cigar-shaped clouds also occur in the US, mainly in spring

66. note the stably stratified layer below, and the more turbulent one above