Friday, October 2, 2009

Nacreous Cloud Pics

More on nacreous clouds and pics taken during Winfly by my trusty little Olympus, which has survived mild freezing 3 times now! (think you'll like this, dad)

As explained during a sunday science lecture by Dr Terry Deschler, atmospheric scientist, nacreous clouds are formed of very small particles like chlorine which refract light very effectively. The angle of refraction is very localized so the brilliant colors in the clouds are constantly changing minute to minute as air currents flow through. Many of these are lenticular clouds- formed by a standing wave of cold air rising up over mountainous terrain. Air must be very cold to form nacreous clouds, so they're generally only seen at very high altitudes over mountains during cold times of the year when there's low-angle sunlight.

The chlorine in the clouds is actually breaking down ozone as we watch- chlorine combines with 03 to form ClO and O2, then ClO interacts further with O3 to form Cl and O2. Thus the chlorine is recycled in the equation and oxygen is formed from the breakdown of ozone.

Atmospheric chlorine comes from natural reservoirs such as acid clouds in the atmosphere. (Interestingly high-flying fighter jets experience etching of glass and metal due to atmospheric acid, and many commercial airliners needed scarred windows replaced in the months after the eruption of Mt Pinatubo released sulfuric acid into the atmosphere). The breakdown of CFCs has added to Earth's natural reservoirs of atmospheric chlorine and resulted in the ozone hole in the Southern Hemisphere. There is actually more chlorine in the skies over equatorial latitudes, but the chemical processes which break down ozone occur at high latitude. Ozone is produced naturally by O2 interacting with the solar winds. Therefore banning of CFCs means eventually the excess chlorine will be naturally cycled out and the ozone layer should reseal, but this will take several generations.

In the meanwhile we enjoy a beautiful pheonomenon with disturbing implications behind it.

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