A Closer Look at Lines in the Sky

#1538 "A longer Reach" Pixels Link

If you are lucky enough to witness a long straight line in the atmosphere, you are seeing a deformation zone. In fact every line in the atmosphere that is not a jet contrail, must be a deformation zone. Deformation zones are very common indeed!

The conceptual model of a straight line deformation zone is pictured. Together the two green arrows pointing away from the central col at "C"  along the axis of dilatation, form the deformation zone. The yellow puffs of wind blowing toward the col along the axis of contraction help to drive the rotational components of the deformation zone. This simple graphic is flat and does not reveal the three dimensional circulations that make every deformation zone line so very interesting.

As shown in the first post in this series "Cloud Shapes and Lines in the Atmosphere", the deformation zone is created by two opposing puffs of air.

In the next post "The Theory of Unified Swirls"… a puff of air was shown to create a three dimensional smoke or vorticity ring. The rotation associated with these two opposing puffs shape the linear deformation zone. A straight line deformation zone is created by perfectly balanced opposing flows which can be stationary in the earth frame of reference.

The X in the middle of the graphic represents the puff blowing into the page. Red colours are used for a upward pointing thumb and blue colours are where your thumb is pointing down. 

In the conceptual model of the deformation zone the companion rotations on either side of the inward puff along the axis of contraction are part of the same smoke ring. I would need a three-dimensional graphic to include the vorticity ring but it is important to imagine it in your mind. What happens to one companion rotation must also happen to its buddy as both are created and driven by the same puff of air.

If the puff of wind blowing into the deformation zone is stronger than the puff on the other side, the following bow-shaped deformation zone must result. The stronger puff creates a more vigourous smoke ring and the cross-section though that ring reveals faster and larger companion vortices.

A convex DZ is bowed in the direction of the stronger flow. A bowed deformation zone cannot be stationary in the earth frame but must translate in the direction of that flow. This is by far the most common shape for a deformation zone in the atmosphere. The side with the stronger wind puff is also more likely to be moist than the other. This contrast makes the deformation zone visible. Air is always going somewhere in an attempt to maintain a balance of heat and moisture around the globe. We call this weather. Perhaps an animation might make these concepts more clear.

There are deformation zones in the sky every day. Watch the cloud along the linear edge for a few minutes to determine which way it is moving. The tracer moisture will be stretched along the deformation zone in that direction. The cloud will always be stretched away from the col in the deformation zone conceptual model. By locating the col relative to your position then you can infer which part of the deformation zone is about to pass over your region.

For example, as you look toward the deformation zone line, if that cloud is moving to your right then the col is to your left. Using your right hand and directing your fingers in the direction of the cloud movement would have your thumb point upward. The red vorticity maximum is likely to cross your location. That means more weather compared to what is on the other side of the col.

Typically the deformation zone is part of the large conveyor belt conceptual model of mid latitude storms and that is where we are headed... soon but not today...

Know the wind, know the clouds and that means you will know the weather.

Phil the Forecaster