When do waves form?
Basically, three ingredients are needed for the formation of atmospheric waves:
mountains / hills
Topographical obstacles are generally necessary to trigger vibrations and thus waves. A rather flat side facing the current (=windward) is conducive to wave formation. The side facing away from the current (=leeward) should be rather steep.
wind
The winds should blow as perpendicular to the mountains as possible at ridge level and above. The current must also have a speed of at least 25-40 km/h. An increase in wind with altitude is also an advantage.
stability of the atmosphere
Another prerequisite is a fairly stable stratification of the atmosphere at ridge height. This means that the decrease in temperature with altitude is only slight or there is even an increase in temperature with altitude (=inversion).
The shape of the mountains and the exact wind and temperature profile of the atmosphere then determine the shape, length and height of the waves. Possible wave breaking also depends on these parameters.
Schematic representation of different atmospheric wave types
Depending on the atmospheric conditions, waves either spread horizontally downstream (A) or propagate vertically upwards (B). In the first case, they are called (trapped) lee waves, while waves of type B are usually referred to as mountain waves in German. (COMET, doi.org/10.3390/atmos12060737)
How do you detect atmospheric waves?
Waves are only visible when the atmosphere at the respective height qatar phone number library has enough moisture. If an air parcel is deflected vertically upwards due to a wave, it cools down while the moisture remains the same. As soon as the dew point is reached, the moisture condenses into small water droplets, forming a cloud. If the air parcel then sinks back into the trough of the wave, the water droplets evaporate again due to the warming. Accordingly, the troughs of the waves usually remain cloud-free, while the crests of the waves are marked by stationary clouds.
Satellite image of the Alpine region
Satellite image from 8 a.m.: Over the Vosges and the Black when spam complaints increase isps may begin Forest, low cloud fields made the lee waves visible this morning. Over the Alps, the strong northwesterly flow triggered vertically propagating mountain waves, which were partly responsible for the high cirrus clouds south of the Alps. (MeteoSchweiz, Eumetsat)
Why mountain and lee waves are important in meteorology
Waves can therefore cause more or less extensive cloud cover and awb directory thus influence the duration of sunshine and temperature. Atmospheric waves also play a role in downdrafts on the side of mountains facing away from the current, i.e. in foehn events.
Lee and mountain waves are particularly relevant in aviation. They are very welcome guests in gliding, as they enable long distance flights thanks to strong and stationary updrafts. Waves, however, usually have a negative influence on other types of aviation. The strong vertical current associated with waves can mean that the pilots can no longer maintain their altitude. Mountain waves can also break at the tropopause, which can then result in severe turbulence.
