Sunday, July 29, 2018

Elly MacKay’s “Red Sky At Night”

Wisdom can be found in the natural world. We just need to look. Elly MacKay’s “Red Sky At Night” returns us to our rural roots. There is no need for technology. There are no equations. Simple scrutiny of nature can lead to understanding the important processes at work in the world. Some of these ancient poetic observations are treasures supported by modern science. Some are simply nice poems. Both are fun.
Published by Tundra Books you can find Elly MacKay’s book at this link.
One piece of weather wisdom is so important that Elly uses it as the title of her book. A red sky at night also graces the cover. Yes that piece of weather wisdom is most important.

Red sky at night, sailor’s delight. 
True (in temperate zones). In some parts of the world, the saying goes, “Red sky at night, shepherd’s delight.” But whether you are on the sea or in the meadow, red skies (but not red clouds) at sunset mean there is calm air in the western sky. By the next morning, that nice weather should be right overhead.  Excerpted with permission from Elly MacKay’s Red Sky at Night (published by Tundra Books, 2018).

A red or orange cloud free sky at night does lead to a sailor’s delight. The path of light from the sun must be unobstructed by its longest path through the atmosphere. Rayleigh scattering from atmospheric molecules leaves only the longest red wavelengths of the direct beam of white light from the sun on the horizon. The short wavelength blues are the first to be scattered followed by the progressively longer wavelengths. I have used the following graphic for years to explain Rayleigh scattering - really.
Only the longest orange and red wavelengths make it to the sailor’s eyes much to their delight. With no clouds getting in the way of the direct beam from the sun there can be no weather and no ascent in the atmosphere to produce any rain. 
Red clouds at night is another story. Red clouds at night, sailors take fright. I am nobody’s poet but this version of the classic weather prose gets the point across.  Those red clouds indicate that there are both moisture and ascent in the atmosphere – there is weather on the way. Cloud droplets in a really moist atmosphere get even larger and scatter every colour out of the direct beam from the sun except of red. The structure of those clouds completes the weather story. If those red clouds appear behind deformation zones as in red streaks in a sunset sky, wind and daylong rain are nigh.

The large particles that comprise clouds are responsible for the Mie scattering of all of the wavelengths of light – even red. That is why clouds tend to be white. All colours are equally scattered by the larger particles. As the particles increase in size more of that energy is forward scattered in the direction the light was originally travelling. Bright red clouds at night indicate that larger particles are scattering the red sunset colours directly into the sailor’s eyes. Abundant moisture makes those cloud droplets larger so that the redder the sunset clouds the more frightened those sailors should be.

The photo I took of these red sunset clouds preceded the biggest snowstorm of that winter. I saw it coming and perhaps should have been frightened. Being a meteorologist I was excited and took the picture instead. 
Warmest regards… Phil the Forecaster Chadwick

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