Thursday, April 19, 2012

Blue Line

In my Creative Scene Investigation (CSI) presentation I often describe the physics of the "white line" on the horizon of a lake. It is typically due to sun glint looking toward a strong source of light - the sun.
A bright line can also occur along a lake shore even with the sun to your back! The distant area is bright because of the surface area effect caused by looking at a distant area of a flat and highly reflective surface - water. In order to be bright these areas must reflect the colour of the sky. Typically the lake surface will be rippled by wind action caused by drainage winds flowing down the river channel leading into the lake. The rippled water surface will tilt some surface of the small waves to reflect light from the sky which "glints" to your eye. The adjacent smooth water surface will be the darker colours of pure reflection from the distant shore. The contrast between the dark pure reflection of the shoreline and the brighter reflection of the sky from the rippled water surface creates the "blue line".
The difference between sun glint and "sky glint" is both colour and the brightness of the line. When one observes sky glint, you can be certain that there is surface wind involved and with daytime heating, it is only a matter of time before the wind blankets the lake with wave action. The "blue line" is an example of that situation.
The low deck of stratocumulus in the western sky was evidence of increasing moisture on the west side of a surface ridge of high pressure that had enforced "blue bird" skies the day before.
No bugs in the paint this morning but a raccoon did show up to see what was happening.

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