Squirrel Suits! (And Mountain Waves)

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I don’t want to lose sight of my blog objective today (mountain wave turbulence, lee waves, rotor clouds, and other types of terrain-induced wind), but as I was thinking about my article an email landed in my Inbox. It was from Mom, wanting to know if I’d heard of people jumping off mountains wearing “winged suits.” In her email was a link to an amazing video, “Grinding the Crack.” I’ve taken Mom for a couple of rides on my motorcycle and I sometimes think she wishes she was 60 years younger — girls in her day didn’t ride motorcycles or skydive or jump off mountains wearing winged suits. I get the idea that if she were 20 years old in 2011, she’d be living her life a little differently.

Jeb Corliss' video, "Grinding the Crack," is the best video I've seen of wingsuit flying. With more than 2,000,000 views, I'm not alone! For the best viewing experience, select 720p and "full screen." Screen grab image: YouTube

“Grinding the Crack” was really distracting. Thrilling activity, cool music and pumping adrenalin while sitting in an office cubicle will tend to get one’s mind to thinking of anything but the office. Guilty as charged. Oddly enough though, there is a direct connection between Mom’s email and the article I was writing for YourWeatherBlog.

So now it’s my turn to distract: Rocket J. Squirrel. Rocky, the smarter of the pair on the Rocky and Bullwinkle Show, could  navigate the skies at rocket speed. Though the sound effects (and his name) suggest Rocky had a rocket, no such thing was ever seen. Perhaps he was an actual flying squirrel? Perhaps he had a winged suit? Am I alone in thinking that the inspiration of wingsuit flying came from Rocky and flying squirrels? Is there a connection between a human in a squirrel suit and terrain-induced wind? Would one influence the other?

Rocket J. Squirrel from "The Rocky and Bullwinkle Show." It's no coincidence Rocky's on the top of a mountain. Image: mentalfloss

Lee, or mountain wave. Image: Wikipedia.Wind is the movement of air. Globally, air (wind) moves between the poles and the equator due to differential heating (hot air rises, cool air sinks; hot air at the equator, cold air at the poles) and is further influenced by the spinning of the earth (Coriolis). From there, forces almost too numerous to mention act and react upon wind to change its speed, direction and buoyancy — from thunderstorms and hurricanes to a fluttering butterfly wing to mountains and valleys and even skyscrapers.

Mountains and valleys. Now we’re getting somewhere! Indeed, these are two features that certainly act upon the wind (and vice versa). A wind blowing perpendicular to a mountain range will flow up the mountain on the windward side and then spin and spiral down the lee side creating lee waves or rotor waves. Even without the perpendicular flow, on a clear day wind on the sunny (warm) side of a mountain can rise upward while in the shadows of the opposite side the shaded (cooler) air can rush downward (same thing late in the afternoon as the sun sets and the air cools, gravity will direct the air downward). These temperature-driven downslope winds are known as Foehn winds. In addition, air reaching a funneling valley will accelerate, pulling additional air down the mountain. And let’s not dismiss the lee wave as a gentle breeze that might ruffle your hair or tip your patio umbrella. It certainly can be, but often it’s been known to damage aircraft both large and small.

Natural or man-made, the affect is the same: trap a cushion of air under the body to slow descent, while controlling direction with body, arm and leg movement. Wingsuits generally have a 2.5:1 glide ratio (for every one foot dropped, 2.5 feet forward are gained). Flying Squirrel image: Wikipedia. Wingsuit image: Jeb Corliss

Thermals, too, could be considered terrain-based wind, though indirectly. Without terrain, thermals would not exist, however it’s not one mechanical force acting upon another. Instead, thermals are a result of convection which in turn results from the uneven heating of the earth’s terrain: as air is heated from below it becomes less dense and rises; as it rises it cools and then descends. Darker surfaces such as brown earth, asphalt roadways and urban areas are good areas for inducing thermals while snow-covered or grass-covered fields are not. Interestingly, bodies of water can go either way, warmer or colder, depending on the characteristics of the air surrounding them: a warm lake in early fall after a cold front could be an ideal source of thermaling columns of air. A talented glider or paraglider pilot can exploit thermal wind and turn it into hours of exciting (and free!) flying.

Workings of a thermal. Image: Wikipedia.

But what about those squirrel-suited dudes like Jeb in the video above rocketing past a mountain wall at ludicrous speed? Good news and bad news, actually. It comes down to skill and an understanding of the weather conditions. The right wind can extend your flying time (and distance), or in the blink of an eye the wrong wind can smack you (with extreme prejudice) into the side of said mountain wall. Which, to me, puts too much at risk for a thrill that can all go wrong with just a slight miscalculation of wind and/or temperature and/or time of day and/or altitude and/or a slight miscalculation in the angle of your control surfaces (aka: hands and feet).

As a meteorologist, knowing how air rises and descends and how the terrain influences those air currents is critical to the daily forecast. As an outdoors adventurer, it’s critical to have an understanding of not only the weather, but of the terrain around you and how it can influence the weather. Paragliders, soaring and ultralight pilots and parachutists need an intimate understanding of the wind and terrain, as well as how they influence each other. But those squirrel-suit guys are just crazy! (Here’s another “squirrel suit” video by Jeb Corliss that will amaze you.)


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