Emirates at Birmingham Airport, UK. When a wing generates aerodynamic lift the air on the top surface has lower pressure relative to the bottom surface. Air flows from below the wing and out around the tip to the top of the wing in a circular fashion. An emergent circulatory flow pattern named vortex is observed, featuring a low-pressure core. The cores of the vortices are sometimes visible because water present in them condenses from gas (vapor) to liquid, and sometimes even freezes, forming ice particles.