Tuesday, May 02, 2006
Cloud droplet phenomena
This image shows how light scattering by small cloud droplets produces multiple effects that are actually all part of the same phenomena. The scene was taken by Leigh Hilbert in Washington State in January ’06. The shadow of the descending aircraft is surrounded by a bright glory (1, 2,) centred just behind the wing where Leigh was seated. Much further from the aircraft shadow is a circular cloud bow (1,2), a form of fogbow (1, 2), produced also by scattering by cloud water droplets. The classical light paths producing it are those of the rainbow (1,2,3) but diffraction by the small droplets produces something much broader and almost lacking in colour. Inside the main cloudbow is a supernumerary arc that, characteristically for cloudbows and fogbows, has more colour saturation than the primary. The more distant clouds at the image top have produced a narrower cloudbow indicating that their droplets were larger.
Posted by Les Cowley at 5:22 PM