Rare Kelvin-Helmholtz Wave Clouds and the Impact On the Aviation Community (Image Credit: Hannah Peters)
Kelvin-Helmholtz wave clouds, aka billow clouds or shear clouds, are a rare sight to see. Kelvin-Helmholtz clouds are named after Lord Kelvin and Hermann von Helmholtz, whom have studied the physics of the instability that leads to this type of cloud formation.
These clouds look like ocean waves breaking as they come onto the shoreline. They can be visually appealing but can produce some underlying concern for pilots--both private and commercial. Associated with an unstable environment, these clouds are areas of vertical displacement of air parcels. The atmosphere is dynamically stable in nature, and if it isn’t, the environment quickly tries to correct itself. This is what makes Kelvin-Helmholtz wave clouds so rare. The strong areas of vertical displacement and higher winds near the upper levels cause the crests to overrun the troughs such as a wave in the ocean. This overrunning results in overturning similar to mountain wave development. These clouds typically form within the stable layer at altitudes above 16,500ft. This process shows the fluidity of the environment, but with the fluid nature there becomes a concern for upper-level turbulence.
This upper-level turbulence is found in thin patches near a strong jet stream. Clear air turbulence (CAT) is most common in association with Kelvin-Helmholtz wave clouds. CAT is nearly impossible to spot due to the small area that it covers, which in turn, makes it more dangerous. Since these clouds have such a short life span with a quick dissipation rate, they are hard to predict where they will occur. Aircraft flying in this layer can experience a brief burst of moderate to severe turbulence. Avoiding the layer where CAT forms due to Kelvin-Helmholtz wave clouds is key to ensuring a smooth, safe flight. As you can see, these clouds can be spectacular in nature but pose a significant threat to the aviation community.
Sources and more information:
©2020 Weather Forecaster Hannah Peters