Wave cloud

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This wave cloud pattern formed off the Île Amsterdam (lower left corner, at the "tip" of the triangular formation of lenticular clouds) in the far southern Indian Ocean.
This wave cloud pattern formed off the Île Amsterdam (lower left corner, at the "tip" of the triangular formation of lenticular clouds) in the far southern Indian Ocean.
Wave cloud pattern as seen from below in southern Algeria.
Wave cloud pattern as seen from below in southern Algeria.
Extensive wave cloud on 16 Jan 2007 at Burra, South Australia.
Extensive wave cloud on 16 Jan 2007 at Burra, South Australia.

Contents

[edit] Formation

A wave cloud is a cloud form created by atmospheric standing waves. These waves are created as stable air flows over a mountain range, and can either form above or in the lee of the range. As an air mass travels through the wave, it undergoes repeated uplift and descent. If there is enough moisture in the atmosphere, clouds will form at the crests of these waves. In the descending part of the wave this cloud will evaporate due to adiabatic heating, leading to the characteristic repeating cloud/clear bands. The cloud base on the leeward side is higher than on the windward side because precipitation on the windward side removes water from the air.[1]
It is possible that convection from mountain summits can also result in the formation of wave clouds. This occurs as the convection forces the wave and lenticular wave cloud into the more stable air above. [2]

[edit] Importance

[edit] Climate Modeling

Wave clouds are typically mid to upper tropospheric ice clouds. They are relatively easy to study because they are quite consistent. As a result, they are being analyzed to increase our understanding of upper-level ice clouds on the earth's radiation budget. Understanding this can improve climate models.[3]

[edit] Recreation

The streamlines in these clouds have the steepest slope where the vertical velocity reaches a maximum value a few kilometers downwind of the lee slope of a mountain. It is in these regions of high vertical velocity that sailplanes can reach record-breaking altitudes.[4]

[edit] Structure

In an ideal model, the wave cloud consists of supercooled liquid water at the lower part, mixed phase (a combination of frozen and liquid water) near the ridge, and ice beginning slightly below the ridge and extending downstream. However, this doesn't always occur. Wave cloud structure ranges from smooth and simple to jumbled (phases occur randomly.)1 Often, ice crystals can be found downwind of the waves. Whether this happens depends on the saturation of the air. The composition of the ice is currently an active topic of study. The main mechanism for ice formation is homogeneous nucleation. The ice crystals are mostly small spheroidal and irregular-shaped particles. Columns make up less than 1%, and plates are virtually nonexistent.[5] Multi-level mountain wave clouds form when the moisture in the air above the mountain is located in distinct layers and vertical mixing is inhibited.


[edit] References

  1. ^ Wallace, John M., Hobbs, Peter V. Atmospheric Science, and Introductory Survey. San Diego, CA: Academic Press, 1977.
  2. ^ Worthington, R.M. "Lenticular wave cloud above the convective boundary layer of the Rocky Mountains," Weather 57(2002):87-90.
  3. ^ Baker BA, Lawson RP (2006) In Situ Observations of the Microphysical Properties of Wave, Cirrus, and Anvil Clouds. Part I: Wave Clouds. Journal of the Atmospheric Sciences: Vol. 63, No. 12 pp. 3160–3185
  4. ^ Wallace, John M., Hobbs, Peter V. Atmospheric Science, and Introductory Survey. San Diego, CA: Academic Press, 1977.
  5. ^ Baker BA, Lawson RP (2006) In Situ Observations of the Microphysical Properties of Wave, Cirrus, and Anvil Clouds. Part I: Wave Clouds. Journal of the Atmospheric Sciences: Vol. 63, No. 12 pp. 3160–3185

See: lee waves

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