Sands of Luce: ripples in the sand

It was very windy on the beach near Stranraer. I noticed that the sand was piling up in ripples like a regular waveform with the wavefronts running perpendicular to the wind direction. I found a brilliant article that explains why https://www.scientificamerican.com/article/why-do-regular-wavelike-s/ In short, the wind gets strong enough to get some sand grains airborne. They hit the ground at a shallow angle and this knocks other sand grains forwards, but only by a small amount. It means that sand is constantly knocked forward a few millimetres at a time on the gently angled slopes facing the wind but there are fewer impacts on the steeper slopes angled away from the wind. It is harder to dislodge sand from there so they define the end of the ripple.