Why swirl marks show up in winter sun

In winter the sun sits low and hits the car at a shallow angle. It acts like a point light, and every fine scratch catches it as a ring around the reflection.

Those rings are wash marring: tiny scratches from grit dragged across the paint by a mitt, a brush or a towel. They were there in summer too; the light hid them.

A two-bucket wash stops new ones. Removing the old ones takes a machine polish, and a test spot on one panel shows how far that will go on your paint.