文:Alex
大家近日在社交媒體上,有否見到一段有夕陽,還有「彩虹雲」的短片?這段影片曝光不久,旋即有氣象學者表示,懷疑影片有造假成分,並不完全真實。
Correction: these two videos of a multi-coloured scarf cloud spotted in Southern China seem to be edited. It is likely the upper/colourful part of the cloud has been added later to both videos from a still image. Cloud colours are over-saturated. ? pic.twitter.com/omkLECESvE
— HoaxEye (@hoaxeye) August 28, 2022
影片題為「彩虹幞狀雲」(Iridescent Pileus cloud),字面意思已表明有兩個現象同時出現。首先是「虹彩雲」(Iridescent cloud)。當陽光穿過雲中大小均勻的微細水滴或冰晶後,透過衍射(又名繞射)作用,雲塊會浮現出彩虹色彩。當太陽位於高層雲或高積雲附近,會較容易出現此特殊光學現象。
另一個是「幞狀雲」(Pileus cloud)。幞狀雲可看作是一頂小帽子。當濃積雲或積雨雲內的強烈對流不斷往上發展,而雲頂又剛好有股穩定而潮濕的水平氣流時,後者會被向上推。隨著高度增加而氣溫下降,水氣會因冷卻而凝結成依附在積雲頂端呈帽狀的幞狀雲。
Fact check
— Scott Duncan (@ScottDuncanWX) August 28, 2022
❌ Original photo stitched into a sunset background and edited into an over-saturated video (which went viral)
❌ Surrounding clouds do not make sense meteorologically
❌ Light angle looks wrong at sunset
Original from Yunnan (China) 16 Aug 2022 by JiaQi Sun pic.twitter.com/oyJdSWRFpN
氣象學者指出,短片中的「彩虹幞狀雲」看來是真的,只是虹彩的飽和度偏高,有被編輯過的跡像。最大問題出自背景的夕陽與彩霞,夕陽的角度看來不可能產生虹彩雲。所以結論是,有人將真實的幞狀雲照片(據報照片由一位中國的天象愛好者孫嘉琪在雲南拍攝)「加工」,安插到一段夕陽影片上,合成出大家在網上見到、令人感到匪夷所思的天象奇景。
??Pileus☁️☁️
— Aesthetic Sharer ZHR (@CGdrawing) August 17, 2022
?Cloud iridescence is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon.
Time: 2022.08.16
Location: Pu 'er City, Yunnan Province, China
Photographer: JiaQi Sun(孫嘉琪) pic.twitter.com/h6RExQ92ew
幞狀雲雖然不常見,但也不算罕有。香港天文台 Facebook 較早前便貼出了由本地天象愛好者 FU Ching Tak,在粉嶺拍到的幞狀雲影片。有興趣的影友可以透過帖子文內的連結,了解更多相關天象知識。