Kelvin-Helmholtz

Rob and I took a walk up Arnside Knot this afternoon in the glorious sunshine. We had hoped to see some butterflies, but they were few and far between. A couple of Dark Green Fritillaries were hiding in the vegetation, and some Gatekeepers. 
The best thing was this lovely spiral cloud which I think is a Kelvin-Helmholtz, caused by two air currents flowing in different directions!