Boundary layer
Written by John Macpherson
Fulmar © John MacPherson
As the quill pen recorded the story of our history, so bird flight writes the story of the wind for us to witness.
Can you read it?
Let me help you understand.
When a steady strong wind moves along a surface, lets choose the sea, it results in a variation in the wind speed called a wind gradient, where the wind speed varies with altitude.
The gradient is strongest near the surface, diminishing gradually with altitude. The air closest to the sea will move more slowly than the air further away due to frictional force between sea and wind.
Birds know that moving in and out of these different wind speeds in certain patterns will allow them to utilise the extra energy created. This is called dynamic soaring.
It differs from conventional soaring in that it does not use rising air to sustain flight, but rather the boundary layer that separates different wind speeds.
Energy is extracted from the air simply by flying in and out of air masses moving at different speeds.
But of course birds don’t really know all this.
They simply feel it.
They just flounder when they are unsupported, and when buoyed up they rise, and soar and glide.
(Just like people.)
And the name of one of the first scientists to investigate this? And whose studies “Observations of Herring Gull Soaring,” (1940) and “Soaring over the Open Sea” (Scientific Monthly. pp.226-252 1942) hints at some of this avian magic?
Woodcock.
A man whose name can now effortlessly soar and glide through the boundary layers of your imagination.
Author — John Macpherson
John MacPherson was born and lives in the Scottish Highlands. He trained as a welder in the Glasgow shipyards, before completing an apprenticeship as a carpenter, and then qualified as a Social Worker in Disability Services. Along the way he has cooked on canal barges, trained as an Alpine Ski Leader & worked as an Instructor for Skiers with disabilities, been a canoe instructor, and tutor of night classes in carpentry, stained glass design and manufacture, and archery. He has travelled extensively on various continents, undertaking solo trips by bicycle, or motorcycle. He has had narrow escapes from an ambush by terrorists, been hit by lightning, caught in an erupting volcano, trapped in a mobile home by a tornado, kidnapped by a dog's hairdresser, rammed by a basking shark and was once bitten by a wild otter. He has combined all this with professional photography, which he has practised for over 35 years. He teaches photography and acts as a photography guide & tutor in the UK and abroad. His biggest challenge is keeping his 30 year old Land Rover 110 on the road. He loves telling and hearing stories.