Unusualclouds非比寻常的云Fromshelfcloudstosupercellclouds,thosewhiteandfluffythingsintheskyarenotalways,well,whiteandfluffy.Some,asyouwillsee,arejustdownrightweirdandwacky.Manyareaportentofbadthingstocome从滩云到超级细胞云，天空中这些看上去又白又软的东西并不总是那么洁白和松软。下面你将看到的云可以称得上千奇百怪，它们当中有很多都代表着灾难即将到来。guardian.co.uk,Thursday23August201218.51BST《卫报》2012年8月23日周四18.51（英国标准时间）Shelfcloud,Minnesota,US.Whenseenfromthegroundshelfcloudsappearaslow,wedge-shapedcloudsandareusuallyassociatedwithseverethunderstorms美国明尼苏达州的弧状云。弧状云刚在地表上出现时看上去像低低的楔形云，通常伴有雷暴。Photograph:SciencePhotoLibrary/RexFeatures图片：科技图片库/雷克斯图片社SouthDakota,US:MammatuscloudsoverSouthDakota.Mammatusisameteorologicaltermappliedtoacellularpatternofpoucheshangingunderneaththebaseofacloud美国南达科塔州：南达科塔州上空的乳状云。乳状属于气象术语，指的是云层底部垂下的细胞型囊状物。Photograph:SciencePhotoLibrary/RexFeat/SciencePhotoLibrary/RexFeat图片：科学图片库/雷克斯图片社CumulonimbuscloudoverwesternAfrica,takenfromtheInternationalSpaceStation(ISS).Cumulonimbuscloudsriseverticallyuntiltheyhitanaturalbarrier,knownasthetropopause(heatmosphericboundarybetweenthetroposphereandthestratosphere),andthenflattenout.Cumulonimbususuallyheraldaseverestorm积雨云：国际空间站(ISS)所摄，位于非洲西部上空。积雨云垂直上升，到达被称为对流层顶（对流层和平流层之间的大气边界层）的天然障碍物，然后开始向四周平铺扩展。积雨云通常预示着猛烈的暴风雨。Photograph:SciencePhotoLibrary/RexFeatures图片：科学图片库/雷克斯图片社Noctilucentcloudsarecrystalsoficehangingaround50mileshighintheatmospherethatcatchthelightofthesunlongafterithassetonthehorizon.夜光云：太阳从地平线升起很长时间后，存在于大气层中50米左右高度的冰晶吸收阳光而形成。Photograph:SciencePhotoLibrary/RexFeatures图片：科学图片库/雷克斯图片社PileuscloudabovetheSarychevvolcanoasiterupts,attheKurilIslands,Russia.Pileuscloudsaresmallcloudsthatformontopofabiggercloud俄罗斯千岛群岛Sarychev火山爆发时出现在火山上空的菌盖云。菌盖云是指体积较大的云团顶部形成的小云团。Photograph:SciencePhotoLibrary/RexFeat/SciencePhotoLibrary/RexFeat图片：科学图片库/雷克斯图片社Actinoformcloudsareonlyvisiblefromspace.Theselargeformationsformray-likepatternsoverhundredsofmiles.Theyareassociatedwithdrizzleandgloomyweather.VeryBritish,perhaps?放射形云只能在太空中看到。这些巨大的云团呈射线形，覆盖范围达数百英里。它们一般预示着小雨和阴天。非常有英国