Fluffy, puffy white clouds in a bright blue must be moving upward. As air rises,it sky. This is one of the first memories of cools. If water vapor and condensation clouds that many of us have. You might nuclei are present,you've got the ingredients remembera peacefultime lying on your back for a cumuliform cloud. When you see looking at the sky above,imagining shapes cumuliform clouds,you can infer that the coming to life in the clouds. weather conditionsare unstable, -- .-', ':,i:::..'t-EEi-#!E#, -- ...it'=. r 1 be in the WOfkS. Ducks, people,trucks, houses, ::i-: - and Cnange may and horsesmight have paraded by as the puffs of bright cloud lavered. Stratus is a Latin word slowly changed. meaning "Iayer." Stratiform You've alreadylearned that clouds form when weather clouds form when water vaPor conditions are fairly stable. They t., condenseson tiny particiesof result from the lifting of alarge, smoke,salt, and other moist air mass. condensationnuclei. But why do some Meteorologists also observe where in the clouds appear pufry and white and others troposphere clouds form. High-level clouds grow to towering mountains? And what form above 5000 meters (m) and are given the about thoseclouds that cover the sky as a cirro- prefix. Middle-level clouds form gray,gloomy mass?Why are someclouds between 2000 and 5000 m and are given the closeto the ground and othersfaint streaks alto- preftx. Low-level clouds form below high above? 2000 m. There is no special prefix for low- Clouds appearas one of two basictypes- level clouds. cumuliform and stratiform. Cumuliform Some clouds may extend from low to high describesthe puffy, sometimesfast-moving levels. They are nimbus clouds. Nimbus and rapidly growing kind of cloud. Cumulus means "rarrtSearing." comes-fromthe Latin word that means "heap." To grow a cumuiiform cloud, air =€ -'1"- 'l:-lil' tukeH6wiiA, LOUDS FatherT LukeHoward is sometimes called thegodfather of theclouds. Howardwas never trained as a scientist,but he loved nature, especiallyweather, from an earlyage. For more than 30 yearsof hislife, he kept a recordof hisweather observations.He presented his first system for classifying cloudsin I802. lt isthe same system meteorologists all overthe world use today. Howardalso discovered that the air over cities is warmer at 6000m nightthan air over the countryside. We call this an urban ,,, heatisland today. cumulonimbus You can describe just about any cloud you observe by its shape and altitude. For example, . An altostratus cloud is a middle-level-layer MIDDLE-LEVELCLOUDS cloud. A cirrocumulus cloud is a high-level puffy cloud. 4000m o d cumulonimbus cloud is a heaped cloud growing from low to high levels, bringing rain. Some low-level ciouds have no prefix and are just altocumulus known as stratus or cumulus clouds. The words that describe clouds are very useful when you're recording weather observations and il,ant to tell someone else what you have observed. Knor,t'ing why different clouds form gives you a - - *2000m good idea of weather conditions in your area. LOW-LEVELCLOUDS stratus Thatwhich nd can clasp. bi"roro" ina poerh von Goethe (1749-1 832) 't '|'rrRlFt\ ltr LOW-LEVELCLOUDS Stratus Thebase of stratusclouds is oftenaround tt) 600 m. Stratusclouds form in stableair. They = appearflat and layered, with no lumps or F F bumps. tt) Stratocumulus Stratocumulusclouds form when warm,'moist air mixeswith drier, cooler air. Whenthis (t) mixturemoves beneathwarmer, lighter air, it J startsto formrolls or waves.lt lools thick, lt = maybring drizzle or lightprecipitation. U F F tt) Cumulus Puffywhite clouds at lowlevels are called ' cumulusclouds. When they are small and scattered,it meansgood weather. These are v) sometimescalled fair-weather cumulus. J -t = I Cumulonimbus Cumulonimbusclouds form on hotsummer days.The sly maystart clear, with little wind. v1 Air heatedby theground rises. Convection E cellsform. Warmair risesthrough the cell z center;cooler air sinks down the sides. A J cumulonimbuscloud forms. lt istaller than a cumuluscloud, with a basebetween 300 and I 1500m. Rainstarts to fall. Thunderstorms maydevelop. MEDIUM-LEVELCLOUDS \t) F Nimbostratus F Nimbostratusclouds are sheet clouds carrying v) rain. Rainor snowfalls almost continuously. 'There = is usuallylittle turbulence. z Altostratus Altostratusclouds appear white or slightlyblue. Theycan form a continuoussheet or look th-] fibrous.They form between 2000 and5000 m. F F Rainor snowmay fall. Sometimesyoucan see ta theSun through an altostratus cloud. F J Altocumulus Altocumulusclouds form between 2500 and 5500m. Theylook like small, loose cotton ballsfloatinE across the s$. Altocumulusmammatus Altocumulusmammatus clouds look tt threatening,but actuallyindicate that the rairyr =tt weatheris almostover. The clouds droop 5> becausethe air is coolingand sinking. r-.1E ') z, Altocumuluslenticularis Altocumuluslenticularis clouds are 4,n lens-shaped.Sometimes they look like flyinE =4. saucers.They form at thetop of a waveof air flowingover a mountainpeak or ridge. iU YZ J u..1 40 HIGH-LEVELCLOUDS Cirrus Cirrusclouds are made of fallingice crystals. Thewind blows them into fine strands. The longerthe strands, the stronger the wind. th Cirrusclouds indicate that the air is dry. Good weathershould continue. o Cirrocumulus Cloudscomposed of manysmaller clouds at a (t) highlevel are called cirrocumulus. Some people = thinkthese clouds look like fish scales. tt is sometimesknown as a mackerel sky.lt may- L) meanthat unsettled weather is onlts *ay. o Cirrostratus Cirrostratusclouds are high-level clouds that coverthe s$ Thecloud is thinand transparent. Youcan see the Sun or theMoon through cirrostratusclouds. \a F F th o JetContrail Thisjet is flyingamonE some cirrus clouds. This couldbe called a human-madecloud. The iet's J' contrailis formedby condensation of water F vaporfrom its exhaust. Z L,) F ul 47 I . Lookat theweather observations your class has recorded on the classweather chart. Ifyouincluded cloud observations, what were the most commonUpes of cloudsT Tryto identi! anyrelationships between the types of cloudsand otherweather observations. For example, when air pressure decreased,did a certainkind of cloudappearT 2. lf stratusclouds fill the slgr for several drys, what does that tellyou aboutthe stability of theairT What kind of weathermightyou expect? 3. Cumulonimbusclouds often form in theafternoon. What weather and Iandconditions might contribute to theirforming later in thedayT (Hint:Think about solar heating of Earthand heat transfer.) 4. Readthe quoteby Goethe on page38. Whatdoyou think he meansT 5. Writeand illustrate a short poem about clouds. 42 -:'hlRf-t.