These are vapor trails and the shape is because they follow local airflow. What’s happening is that the engine is changing the pressure/temperature in such a wa

These are vapor trails and the shape is because they follow local airflow. What’s happening is that the engine is changing the pressure/temperature in such a way that the localized atmospheric humidity is equal to its dew point. Basically the air has reached the maximum humidity and the water is condensing. It’s also really cool to see, since normally it would be invisible, but the angle of the sun makes it possible to see.