Anyone who has ever sat and watched in silent awe at the unfolding Elysium, splendour as you climb past and above layer upon layer of linen smooth roiling fields of cloud will, like me, find any description inadequate.
Using wave to gain the dizzy heights of Diamond and above has become commonplace. The process of wave propagation is fairly well understood, if still a little difficult to comprehend. Although a vivid imagination helps. I think its best to leave the scientific analysis to the people who understand that sort of thing. Tom Bradbury‘s excellent. book Meteorology and Flights a must for every pilot, and his article in this Yearbook will give a far better insight than I can to the mysterious workings of the atmosphere.
Although an understanding of the theory is important, it must be backed up with practical instruction which is what I hope this article will do.
The first obvious problem is how do we know it is there. Apart from other gliders climbing in the stuff, what clues are we going to be able to see from the ground that will help us?
Most of the time we have to work for rewards and become used to sporting subtle clues.
The days when wave presents itself like a ladder in the skies, offering an easy climb to Diamond or above, are few. Most of the time we have to work for rewards and so become used to spotting the subtle clues. There are three main cloud formations that will help.
First the rotor cloud.
This is a cumulus type cloud (fractocumulus) which may take the form of a few feathery wisps of ragged tendrils, a single bundle of cloud or of a long roll lying across the wind. Any formation should be investigated; search on the upwind side, ideally above its base. it will not necessarily have any particular form, although sometimes its upwind edge and its crest may be smooth and laminar. At times you may see the cloud rolling, building on its up- wind side and decaying on the downwind side, such that it remains stationary over the ground. The air which lies within these clouds can be very confused and chaotic as can be seen at times from the tumbling effect.
Rotor clouds will form if the air is moist at low levels, their base generally corresponding to the base of other convective cumulus for that day. Lift may be very good on the upwind side then again it may be very broken, turbulent and difficult to use. it varies. The rotor cloud may exist all day or it may be transient, hopping around into or downwind or disappearing altogether. There are days when the climb above the rotor reveals a definite system with well marked lenticular and other days when the only cloud indications are the low level rotors. if this is the case it does not necessarily mean the wave lift ceases above the rotor cloud; it simply means the air above these clouds is too dry to form lenticular. Climbs in excess of 20,000 ft have been experienced with completely blue skies above the lower rotors.
The classic wave indication is the lenticular cloud with its incredibly smooth edges and dinner plate appearance. Sometimes there are single slivers of gossamer fillets, other times gigantic walls formed by millions of tons of air and vapour on the move. They must be the most photographed things in the sky, appearing motion- less, hanging in space. They, like the rotors, are stationary relative to the ground. indeed the wind can be said to blow through the lenticular, ascending and condensing any water vapour on the upwind side and descending and evaporating that vapour on the downwind side, It follows, therefore, that we should fly upwind of these clouds in the rising air in order to climb.