Wednesday, July 3, 2013

Hole Punch Cloud Image Captured Mimics AIM’s Noctilucent Clouds

HU summer student Kyle Elliot captured this hole punch image by the HU Dining Hall
Hole Punch Cloud Image Captured Mimics AIM’s Noctilucent Clouds

Hampton University summer session student Kyle Elliot recently captured an image of a low altitude cloud feature that mimics those seen in Noctilucent (NLCs) or “nightshining” clouds. This usually occurs some 40 miles higher in the atmosphere.   NLCs are being studied by the Aeronomy of Ice in the Mesosphere (AIM) satellite mission led by HU Professor Dr. James Russell.

A “hole punch” cloud, which Elliot observed outside the HU dining hall, usually occurs when an aircraft pierces through cloud layers triggering the formation of ice crystals as air is forced around and over the aircraft’s wings.  This patch of air, after passing over the aircraft, expands and cools by as much as 20 degrees Celsius compared to the surrounding environment. When an altocumulus cloud layer is present, the patch of air left by the aircraft causes the super-cooled water droplets contained within the cloud to rapidly transform into larger ice crystals. The large ice crystals, being heavier, fall out of the cloud and evaporate, leaving behind a hole. 

Hole punch clouds, like the one in the picture, are similar to those found in images collected by the AIM satellite; atmospheric scientists call these high altitude features ice voids. Since 2007, AIM has observed NLCs at heights of about 50 miles above the earth.  They occur on the edge of space and are the highest clouds on earth, forming at temperatures of minus 135 degrees Celsius.  When the delicate temperature balance in the upper atmosphere is disturbed by processes, such as meteorites entering the atmosphere, ice voids appear in the NLC layer that resemble the hole punch cloud seen over Hampton.

Over the past 30 years, NLCs have been increasing, getting brighter and they are appearing at lower latitudes, suggesting a possible connection with global change processes near the earth’s surface.

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