2020 January 10

Nacreous Clouds over Sweden
Image Credit & Copyright:
P-M Hedén (Clear Skies, TWAN)

Explanation: Vivid and lustrous, wafting iridescent waves of color filled this mountain and skyscape near Tanndalen, Sweden on January 3. Known as nacreous clouds or mother-of-pearl clouds, they are rare. This northern winter season they have been making unforgettable appearances at high latitudes, though. A type of polar stratospheric cloud, they form when unusually cold temperatures in the usually cloudless lower stratosphere form ice crystals. Still sunlit at altitudes of around 15 to 25 kilometers the clouds can diffract sunlight after sunset and before the dawn.

Nacreous 瑞典上空的珍珠云
P-M Hedén (Clear Skies, TWAN)

说明: 1月3日,在瑞典Tanndalen附近,山峦和天空笼罩在鲜明飘忽的彩云之中。这种被称作珍珠云或珠母云的罕见现象,在这个北方高纬度地区的冬季出现,令人难以忘怀。在通常无云的平流层下部,当温度异常寒冷时会生成冰晶,从而形成这种极地平流层云。在日落后和黎明前,15至25千米的高空仍有阳光照射,同时云层还能对阳光形成衍射。(北京天文馆 曹军)

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