Squadron of Central Coast kites

Chloe and Sean Lindsey thrill to a squadron of kites on a windy Central Coast day.

Wednesday will mark the first day of spring with rain showers; however, blustery northwest winds will follow Thursday.

Anyone who’s ever lived along the Central Coast for any length of time knows springtime means strong northwesterly onshore winds, perfect conditions for flying a kite.

Brian Smith lived near my home where I grew up in Santa Rosa back in the 1960s and ‘70s. He built a 14-foot-tall classic diamond-shaped kite with the spine, spar and frame constructed of wood and a ballast tail that used an old canvas car cover cut into large bows.

When the winds were strong enough, he flew that kite in a broad open field near Mark West Elementary School with a tether made of braided green tuna line on a big wooden spool.

The line was rated at 300 pounds of force before it would break.

To fly that behemoth, he wore thick leather welder’s gloves to prevent rope burns.

I vividly remember the amount of pull that kite exerted on the tuna line as we helped him bring the kite back in.

With that much force, we wondered, how high could a kite fly into the atmosphere?

To start, “A kite is defined as a tethered aerodyne deriving all its lift from ambient winds and unassisted by any ‘booster’ such as a rocket, balloon, gas, motor, electricity, explosives or other applied devices,” according to the American Kite Fliers Association.

The most significant limiting factor for high-altitude flying is the aerodynamic drag on the tether line.

You see, as the wind speed doubles, the force on the line quadruples.

If the line is too thin it will break; but if it’s too thick, its drag will keep the kite closer to the Earth’s surface — a delicate balancing act indeed.

Well, for many decades, the world kite-flying altitude record stood at 12,471 feet, set in 1896 by A. E. Sweetland and Henry Helm Clayton.

They used a Hargrave box kite with about 86 square feet of sail that resembled the front wing of the Wright Flyer; they used piano wire with a breaking strength of 330 pounds for their tether line.

That record was broken by Richard Synergy on Aug. 12, 2000, when he flew his delta wing kite named “Millibar Messenger” to an estimated 14,509 feet in a farmer’s wheat field near the town of Kincardine, Canada.

Millibar Messenger had a 30-foot wingspan with a total surface area of 270 square feet.

Robert Moore and his team broke that record 14 years later when his kite reached 16,009 feet — a little more than 3 miles — above its launch point on a sheep ranch near Cable Downs in Australia on Sept. 23, 2014.

Depending on the latitude and the atmospheric conditions that day, Moore’s kite may have reached the 500 millibars of pressure used to determine the atmosphere’s thickness.

Let me explain:

Meteorologists estimate the thickness of the atmosphere by analyzing 500-millibar upper-level charts. In other words, the chart will tell you where the air density decreases by half.

At our latitude, it usually varies around 18,000 feet. Those are the altitudes where the jet stream or upper-level winds reside.

During the winter months, those winds can reach more than 150 mph.

The kite Moore used to break the world record was also a delta wing. It measured 21 feet wide and 12 feet high and carried a GPS unit to measure altitude.

At the kite’s zenith, more than 41,000 feet of high-strength Dyneema braided line was reeled out — and in — from an electric winch on a trailer that could have been designed by Rube Goldberg.

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John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Follow him on Twitter @PGE_John.