Thursday, July 12, 2018

Noctilucent Clouds

from: NASA APOD


Noctilucent Clouds over Paris Fireworks 
 
  Video Credit & Copyright: Jean-Luc Dauvergne (Ciel et Espace); 
 
Explanation: It's northern noctilucent cloud season -- perhaps a time to celebrate! Composed of small ice crystals forming only during specific conditions in the upper atmosphere, noctilucent clouds may become visible at sunset during late summer when illuminated by sunlight from below. Noctilucent clouds are the highest clouds known and now established to be polar mesospheric clouds observed from the ground. Although observed with NASA's AIM satellite since 2007, much about noctilucent clouds remains unknown and so a topic of active research. The featured time-lapse video shows expansive and rippled noctilucent clouds wafting over Paris, France, during a post-sunset fireworks celebration on Bastille Day in 2009 July. This year, several locations are already reporting especially vivid displays of noctilucent clouds. 

Veins of Heaven
 
Image Credit & Copyright: P-M Hedén (Clear Skies, TWAN)
Explanation: Transfusing sunlight through a still dark sky, this exceptional display of noctilucent clouds was captured earlier this month above the island of Gotland, Sweden. From the edge of space, about 80 kilometers above Earth's surface, the icy clouds reflect sunlight even though the Sun itself is below the horizon as seen from the ground. Usually spotted at high latitudes in summer months the night shining clouds made a strong showing this July. Also known as polar mesopheric clouds they are understood to form as water vapor driven into the cold upper atmosphere condenses on the fine dust particles supplied by disintegrating meteors or volcanic ash. NASA's AIM mission provides daily projections of noctilucent clouds as seen from space.

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