Images: MSBWX (Click on image for larger view)
NOTE: Two different "contrails" observed over Mossel Bay this afternoon on the same flight path. The first contrail (first image) is actually a distrail. Distrail is short for "dissipation trail". Where an aircraft
passes through a cloud, it can clear a path through it; this is known as
a distrail. Because the plane's contrail is not yet visible a distrail
looks like a tunnel through the cloud if the cloud is very thin. This is the first time I observed a distrail in the Mossel Bay area. Distrails are created by the elevated temperature of the exhaust gases
absorbing the moisture from the cloud. Clouds exist where the relative humidity
is 100% but by increasing the temperature the air can hold more
moisture and the relative humidity drops below 100%, even for the same
absolute moisture density, causing the visible water droplets in the
cloud to be converted back into water vapor.The second image reflect a normal contrail ("solid" vapour) seen regularly in this area.
Contrails or vapor trails are long thin artificial (man-made) clouds that sometimes form behind aircraft. Their formation is most often triggered by the water vapor in the exhaust of aircraft engines, but can also be triggered by the changes in air pressure in wingtip vortices or in the air over the entire wing surface. Like all clouds, contrails are made of water, in the form of a suspension of billions of liquid droplets or ice crystals.
Depending on the temperature and humidity at the altitude the contrail forms, they may be visible for only a few seconds or minutes, or may persist for hours and spread to be several miles wide. The resulting cloud forms may resemble cirrus, cirrocumulus, or cirrostratus. Persistent spreading contrails are thought to have a significant effect on global climate.
- MSBWX + Wikipedia
