Aug 17, 2018
Thermal Crossings Blog Update #5
Published June 17, 2016
Free Flying — ridge lift, thermals, and the mythical convergence line
Paragliding has become my main form of transport when in the hills. How far I fly depends on my ability to take advantage of specific weather phenomena to gain altitude. Why over complicate it?
Sometimes, common things such as clouds are key to doing the extraordinary…
Incase free flying is new to you, all non-powered glider aircraft require height to be able to cover distance. The more height, the further you can glide.
To find lift, we use the help of a variometer (vario) which is a flight instrument that lets out acoustic beeps when it measures any gain in altitude.
For years, I took to the sky and I climbed relying solely on the sound of my vario. Despite this over simplistic “turn-when-it-beeps” flying style, I still managed to stay up and cover distance — you gotta start somewhere right…
But what’s behind the BEEP? Let’s explore the fascinating conditions that allow us to cover some great distances surfing the Earth’s atmosphere.
But first, here’s an appetizer… as proof that this isn’t just fantasy.
Birdseye View from +2000m ASL as I glide south, on route to St Andre les Alpes from St Vicent
With that said, here is a look at the three main weather phenomenon that make such non-powered flights possible.
Ridge lift
When taking off with a paraglider, we prefer a gentle breeze hitting the slope head on. This makes inflating the wing and taking off effortless, but it can also produce a band of lift that we can fly through to stay up.
Basically, when the wind hits an object like a mountain, it can’t go through it. Instead, it flows upwards on its way over it.
With the right ridge shape, wind speed, and direction, this upward flowing wind is enough to keep paragliders afloat.
It can’t take you much higher than the ridge, though, but it does allow you to soar and stay up — buying time that can be used to search for a thermal (explained a little later).
Ridge lift can be used to cover distance quickly too, by allowing us to soar along the length of the ridge without losing altitude! You’ll often hear pilots refer to this as ridge running — great fun!
But ridge lift can only take you so far. To be able to jump one valley to another, or to fly over wide rivers and tall peaks, we often need to find a way of gaining some serious altitude.
The solution… Thermals.
Thermals
Thermals are rising columns of warm air. They release from the Earth’s surface and will often rise up thousands of meters — taking with them dust, insects, and moisture.
It’s this process, for example, that’s responsible for clouds, thunderstorms, and rain.
Birds, like this European honey buzzard that flew from Reitz to Finland last year, are masters of making good use of these rising columns of air to fly hundreds of kilometers in a single a day!
It’s by understanding thermals as well as having the skills to climb in them that’s key to unlocking the big distance flights made with paragliders, or any glider aircraft for that matter.
But how do they work?
The Earth’s land mass is made up of lots of different surface types — sand, grass, forest, rock, and concrete to name a few. When the sun heats the Earth, some surfaces heat up faster than others, which in turn, heats the air these surfaces are in contact with. When this heated air mass gets hot enough or is disturbed in some way, it can lose its grip with the ground…rocketing skywards as a thermal!
It’s no joke either. We’re talking about a serious amount of moving air!
The last time I asked a physicist friend to crunch the numbers, I remember him mentioning that a mid sized thermal in the alps could be in the range of +70,000,000 KG of displaced air… and for the record, a cross-country paraglider weighs about 4.5kg.
Explaining how we search, find, and use thermals to climb up to the clouds is outside the scope of this post, but here’s a great resource by Will Gadd.
Convergence Line
The next major meteorological phenomena that allows us free flyers to cover good distance in the air — quickly — is absolutely magic… especially when you can get it right.
When two winds meet, just as when wind hitting a mountain face can create ridge lift, two colliding winds can also create rising air.
And just as with thermals and ridge lift, it’s a condition we can exploit with a paraglider.
What makes it so magic is that these lines of lift can stretch for many miles. But unlike ridge lift, this lift can be present all the way to cloudbase. What this means is that once you’ve used a thermal to get up, you can remain high by flying through an entire air mass that’s getting jacked up and over another airmass.
Let’s take the famous convergence line that regularly sets up across Catalonia as an example, because I know it has local pilots hooked on trying to ride it…and regularly results in +100km flights being made.
In the wind forecast below, notice how from Reus (bottom left), that there is a line heading to the top right where a north-westerly wind is predicted to run into a south-easterly sea breeze. The wind coming ashore hugs the ground while the northwesterly gets lifted over the heavier seabreeze, creating long lines of rising air that can be ridden North…amazing!
Final thoughts
Free flying means different things for different pilots. Some push for distance, some for height, some for a relaxing time in the sky.
But whatever the goal…so long as the pilot wishes to stay up a little longer than a simple glide down a mountain, you can be sure that they’ll need to make good use of one or more of these three weather phenomenon.
To fly well is hard and like most things, it can take a lifetime to master the craft. But if you have ever dreamt of flight, don’t let the learning curve put you off. Paragliding is still the most accessible free flying sport available today.
With just two break lines and a pedal, you can soar with vultures, climb up and into clouds, as well as cover hundred of kilometers in flight, using nothing but the wind and sun’s energy!
What are you waiting for?!
Google “paragliding school [your city]”, and check the sport out for yourself.
And remember, one flight at a time, guys!
Thanks again for the support and happy flying.
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A bit about me: I’m Rhys! I’m a 28-year-old adventure addict from England. In 2017 I crossed the Pyrenees, powered by the elements…rock’n a high performance paraglider. I turned the project into the most interactive adventure of it’s kind. Here’s a sneak peak into day-9, where we flew for 7 hours, covering more than 137km in-flight. The project began as a crowdfunding.
Follow me on Twitter at @AgileExistence
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