Members will associate Wave with a 500 mile drive to the Highlands and a week spent looking at the drizzle through a pub window. Believe it or not, wave is very much part of gliding at Southdown. Think of that final glide from Midhurst where the vario stayed jammed on four knots down and a Wild Brooks landout looked ever more certain. Have you wondered why there is a Blue Hole over Parham in certain wind directions ? Why is there no lift in an a place that all the text books say should be a perfect thermal generator ? An understanding of wave is one of the pieces in the fascinating three dimensional game of chess that is gliding. Very occasionally, you can soar in wave at Southdown.
In a south wind, the Sussex Downs are a classic wave generator. They have a shallow up wind slope and a steep down wind slope. The only problem is that they are only 600 foot high. However they can still generate wave which can take you up to the airspace. It is a just a question of recognising the conditions which will make it possible.
The first thing is to understand is that air has considerable mass. A meter by meter column of air weighs ten tonnes. Imagine this column of air traveling up from Worthing and suddenly descending to Storrington. As it descends, the air pressure increases. As the pressure increases, so does the temperature. As the temperature increase, the air becomes more buoyant and it starts to rise. The momentum of the air column carries it way beyond the stable level and it cools and descends again.
In the right conditions, this will be repeated many times downwind and can be active to a great height. If you want a simple analogy, think of a heavy bag of shopping suspended off a bicycle handle bars with an elastic strap. If the bike goes over a bump, the bag will continue to go up and down and will trace a wave pattern. The faster the bike goes, the longer the wave length.
By David Rhys-Jones