Vermont. August 2012. Refraction, ionization, evaporation, condensation, convection, static electricity and the rotation of the earth are some of the natural processes that create many wondrous events visible in our sky. It is hard to think about all those things when it is raining cats and dogs and there is lightening crashing around you. There is an old pilot’s cliché, “It’s not the clouds that get you; it’s the rocks in the clouds.” Well for flyfishers, “It’s not the rain in a storm that gets you, it’s the lightning.” When lightning streaks the sky it is time to head for the car and once you are in relative safety and cannot fish, you have time for some idle speculation.
How strange a summer thunderstorm might seem to an extraterrestrial plunked onto the surface of the earth. A storm replete with towering altocumulus clouds, lightning, thunder, hail, down pouring rain and high winds? What would our visitor think of a rainbow following the storm or the steamy tendrils of mountain spirits rising from our ridgelines?
Our understanding of the natural forces that cause thunderstorms does not lessen our amazement when we experience one. Most know that when the sun heats the earth, it heats the air that rises. If the air holds sufficient moisture in the form of water vapor and if the air aloft is cool enough, the vapor condenses into clouds. The clouds associated with thunderstorms might reach an altitude of 12 miles, known as Armstrong’s line, where the force of the upper winds blow the clouds flat forming the classic anvil like flattop.
Clouds produce rain when two things occur simultaneously, the humidity in the cloud reaches super saturation moisture levels and there are particles around which water drops can form. Super saturation happens when humidity levels exceeded the airs ability to hold that humidity as vapor. But in the absence of ions or dust particles even super saturated air, up to 700% humidity, will not form water drops. Once there is super saturated air and particles or ions to form raindrops, it rains.
A flyfisher wearing waders and a raincoat usually has enough protection to keep them fishing in the rain that is until the clouds flash lightning. Lightning releases a primal fear in anyone who sees it even from a safe distance and well it should. Now, think about how strange this phenomenon would seem to someone who has never before seen lightning.
A bolt of lightning can be from one inch to one foot in diameter depending on the phase (earlier to later) of the stroke. The lengths of lightning strokes vary, up to two miles long and it happens in milliseconds with a big stroke releasing several billion volts of energy. When you see lightning, you are not seeing the electricity but the air molecules glowing from the tremendous heat of temperatures of over 50,000 degrees Fahrenheit caused by the stroke as it passes through the air.
Thunder is a shock wave, the after affect of heating the air molecules to such a high temperature so quickly. As loud as thunder from a close stroke can be, the sound represents only about 1 percent of energy of the shock wave. You can only hear thunder at a maximum distance of about seven miles because the air molecules between the listener and the shock wave absorb the sound.
Distilled water is not a great conductor of electricity but the amazing ability of water to dissolve other substances turns it into one. When substances dissolve, the molecules break apart into negatively and positively charged ions and they are only too happy to conduct electricity.
Then there are the properties of the flyrod usually made of graphite, the most used material in constructing flyrods these days. Graphite is a great conductor of electricity. Therefore, the ions in the water making it a good conductor and the conductive properties of graphite, adds up to a flyfisher who continues fishing during lightening becomes a grounded target waving a lightning rod above their head. A bad choice that could lead to fried fisher.
The clouds began to clear. As we stepped out of the car, the final act of this extraordinary weather show was a lovely multicolored streak that hung in the sky. There were two rainbows, one above the other with a darker strip between them. The upper one being fainter and its color stripes an exact reversal of the order in the primary rainbow.
Rainbows have enticed such luminaries of science as Sir Isaac Newton and Roger Bacon down through the ages to study them. They defined the angle from the path of the sunlight to where the rainbow forms, 138 degrees for the primary rainbow and if one is formed, 130 degrees to the secondary rainbow. The darker space between the two rainbows is the “Alexander dark band” named after another rainbow researcher, the 3rd Century Greek philosopher Alexander of Aphrodisias.
As much fun as it was to speculate on how strange the storm might seem to our extraterrestrial visitor, the storm passed so it was time to go back to fishing, enough of these idle speculations.
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David L. Deen is River Steward for the Connecticut River Watershed Council. CRC is celebrating 60 years as a protector of the Connecticut River.