Kristy
This is the first time I have looked at your photo and that is the best Cirrus Kelvin - Helmholtz cloud I have seen other than a picture shown in a textbook. They are very rare and I have only ever seen one of these. Well done for spotting it. After looking at your photo, I went searching in my weatherbooks for a description.
How they form:
I have gone to my book 'Weather" by Richard Whitaker (1997) to get a better description on this cloud.
It is a slender horizontal spiral of cloud but tends to dissipate only after a minute or two after forming and hence "rarely observed".
It is a kind of Cirrus cloud resulting from wind shear. Wind shear occurs when a layer of air slides across another layer moving at a different speed or in a different direction or both. This gives rise to vertical eddies that produce a pattern or air waves.
In most cases, wind shear creates a series of gently undulating cloud formations along the tops of the waves. With Kelvin Helmholtz formations, eddies are more powerful and carry the cloud over the peak and down the other side so that the waves break in the manner of ocean waves breaking as they approach the shore. As the waves complete a circulation, they create a distinctive corkscrew pattern.
The cloud was first described by Baron Kelvin (1824 - 1907) and Hermann Von Helmholtz (1821 - 1894) hence the name.
The presence of the cloud indicates a degree of wind shear that is likely to produce moderate to severe turbulence at cloud level. In the absence of cloud, the same process can be a major source of clear air turbulence at high levels (Weather, Richard Whitaker, 1997 (P214).
Hope this is of assistance to you.
Harley Pearman
