Noctilucent Clouds

In the evening of the 14th of Juli 2009

 Fuerstenfeldbruck, South Germany

     in deutsch

 

Noctilucent clouds appears in a height from 80 to 95 km. At the edge of the terrestrial atmosphere in the so-called Mesopause temperatures of -80 to -90C° usually prevails. An adiabatic relaxiation* of the along-transported water lowers the temperature of these clouds to apprx. -140C° down. Here a crystallization at smallest dust particles takes place. This particles were inserted by past volcanic eruptions and innumerable space starts. If at all, these clouds appears mostly in July and August. (Very seldom to observe this phenomena in South Bavaria!)

How you can differentiate this rare appearance on the western horizon from e.g. normal veil clouds at sunset? The singular steel-blue colouring as well as the enclosed filigrane feathery or honeycomb pattern are remarkable. Other formations are possible.

     

Normal veil clouds are situated up to 13 km in the troposphere. While they appear rather grey, the noctilucent clouds appear gleamingly. The dawn retards up to one hour, and when beside these clouds the stars emerge, even the most oversleep observer would have to notice the luminescent difference.

  

And this is the view of the celestrial phenomena observed by Andreas Kaiser from Trier/Germany (e-mail)

Leuchtende Nachtwolken 2009   Leuchtende Nachtwolken 2009

It is not sure if noctilucent clouds stands in connection with sun minimas (smallest solar activity in the cycle of approximately 11 years). If so, we are straight in an unexpected long minimum.  ---> therefore!

“Stay tuned” for the next weeks.

*adiabatic relaxation: short, the reduction of temperature of a gas or a mixture by relaxation (e.g. decompression, principle air-pump)

 

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 ©  2009 photos und text by Thorsten Boeckel, last modification 14.07.2009