Exhaust trails – are formed at high altitude, due to vapor trails, due to these vapor trails, condensation takes place in exhaust gases of engine.
Exhaust Trails – In combustion process hydrogen & carbon in Aviation fuel are burned, the exhaust is composed of a colorless gas, which is a by product of the burnt hydrogen.
Both of these by products are invisible as long as the humidity of the surrounding atmosphere has not reached the Saturation point.
The water vapor will remain invisible as long as the humidity of the surrounding air has not reached its saturation point.
Warm air can hold much more invisible water vapor then can cold air before it becomes saturated.
In extreme low temperatures encountered at high altitudes, the cold air is not capable of absorbing the excess water vapor coming out of the exhaust.
Therefore the water vapor forms into water droplets or ice crystals due to condensation into visible cloud, known as Exhaust trails.
Wing tip vortices are formed at wing tips due to the low pressure area above the wing & high pressure area below the wing. The air at high pressure from below tends to come above the wing at low pressure. If pressure is low in cold temperatures and the humidity is high, theses vortex can be seen by the condensation of moisture caused by the decrease of pressure in the vortex.
Wing tip trails form When humidity of air is high it causes cooling called condensation, forming cloud like trails called wing tip trails on wing tips.