We are always happy to receive feedback and questions from our users. This time, a user sent us a picture of a fascinating cloud formation. We have interpreted this phenomenon and would now like to share this with all interested weather enthusiasts:
Sometimes, the sky is decorated with contrails when planes fly over our heads. The physical explanation for these contrails is the water vapour in our atmosphere. Depending on an air layer's pressure, temperature and humidity, certain amounts of water can be stored in the gaseous state. The combustion of the aircraft fuel paraffin produces additional water vapour and carbon dioxide. This can lead to a brief supersaturation of the water vapour so that the saturation vapour pressure is exceeded.
Consequently, aerosols such as soot and other suspended particles, also emitted by aircrafts, serve as condensation nuclei. Water vapour turns into liquid water on the surface of the condensation nuclei - and a human-made cloud is formed. Depending on the nature of the air layer, these cloud streaks persist. They dissolve faster in dry air than in humid high-altitude air, where they can continue to grow. The water droplets freeze into ice crystals or remain liquid, depending on the temperature.
Let's look at the picture: The horizontal stripe intuitively suggests a contrail that seems "broken". The lower cloud appears to be a longer contrail that has already grown somewhat in width and in which the parallel stripes are thus blurred. The spreading and persistence of the cloud happened locally so that small-scale differences can arise.
(Image by Christine Marquitan)
Unstable air masses can explain the interruption of the upper contrail. In many cases, local processes in the atmosphere create such dynamic conditions. The formation process depends on temperature, pressure and humidity. These meteorological variables vary in the different altitudes of the atmosphere, which can be analysed with our weather maps.
For example, previously condensed air at the edge of these clouds may have sunk, leading to a "blurring" and, thus, dissolution of the condensation line due to the air's temperature change (in this case, warming) during the descent.
Another explanation could be that the condensation did not occur during the aircraft's flyby because the air may not locally fulfil the conditions for forming the streak, or dry air masses rose or descended in the meantime. Boundaries in the atmosphere can, therefore, not only be defined vertically but also horizontally.
In other areas, such horizontal boundaries can also be created by wave movements, for example, as is the case behind mountains in the Lee area.
We are happy to give you a small insight into the diversity of the atmosphere, which provides us with a strange but exciting cloud. Feel free to share your cloud formation pictures.
