Wave Clouds of Australia
From silky filaments to high altitude cirrus and storm bearing
cumulonimbus, clouds are one of the most fascinating weather phenomena.
Clouds are composed of water and indicate the weather condition of any
place. In Australia, weather observers send regular reports to Bureau of
Meteorology on cloud types, heights and the amount of sky covered by
clouds.
What are wave clouds and how are they formed?
A wave cloud is created by the atmospheric internal waves. These white
clouds form a thin layer in the atmosphere where the temperature is more
or less stable.
When air passes through the internal wave, the air undergoes continuous
up and down movements like waves on the surface of a lake. When the
moisture laden air reaches the peak of the wave where the temperature is
cooler, the air cools down and its moisture condenses into cloud. In the
lower part of the wave, the cloud will evaporate because of adiabatic
heating thus forming the vertical rows of cloud bands.
Wave clouds can also be formed by convection from mountain peaks. When
the convection forces the internal wave and the lenticular wave cloud
into the more stable air above, wave clouds are formed.
Multi-level mountain wave clouds are formed when the moisture in the air
above the mountain is placed in separate layers and vertical mixing is
reduced. Moreover, the base of the wave cloud is higher on the leeward
side than the windward side because water is removed from air due to
precipitation on the windward side.
Structure of the clouds
The wave clouds generally consist of highly cooled liquid water in the
lower part, a mixture of frozen and liquid water near the edge and ice
below the edge, which extend downstream. This is not the only structure.
Sometimes, ice crystals are found downwind of the waves. But this
phenomenon completely depends on the saturation of the air. The wave
cloud structure ranges from simple to jumbled structures. These
formations occur haphazardly. The ice formation takes place in wave
clouds due to homogenous nucleation. The ice crystals are mainly
spherical and irregular in shape.
Importance of wave clouds
The wave clouds are generally found in the mid to upper troposphere and
contain ice. Since these are quite consistent, they are easy to study.
Wave clouds are regularly analysed to study the upper level ice clouds
on earth’s radiation budget and they are extremely helpful in improving
climate models. The Gulf of Carpentaria, Australia is famous for its
regular wave clouds which frequently form in the spring.
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