Cloud Edge Shapes - The "Backward S" Deformation Zone

#2065 "Summer Cirrus" (Singleton Lake, Ontario)

What does it mean if a shifting wind veers? A more global visualization is to take your meteorological Coriolis force hand and point your thumb down. I will explain...

Coriolis Hand with Thumbs Down
Warm Advection

That magical Coriolis appendage is your right hand if you live in the Northern Hemisphere and your left hand if you are down under, south of the equator.  The thumb of your Coriolis hand pointing down, will force your fingers to curl in the same direction as wind shear resulting from warm air advection. The following examples will be for the northern hemisphere as that is where I live and paint. I will try to use the more Global phrase “warming wind” instead of the more nautical and historical term "veering". 

To watch the warming wind veer, implies that the wind shift occurs over a period of time. Historically and mathematically, meteorologists have only considered what is happening when winds veer with height. The answer to both questions is that warm air is being advected by a veering wind, whether that change occurs in space or time. 

Wind Veering with Time Moves Warm Air Northward

Companion Swirls straddle the inflows
Paired Swirls see each other are across the DZ

What impact does a warming wind have on our deformation zone (DZ) conceptual model. Let’s start with the simple straight line DZ. The DZ Conceptual Model is a dynamic concept and how it changes, reveals the weather. The following graphics describe the cause and effect of how the changes in just one component of the DZ Conceptual Model is communicated to the other nine components. It takes longer to explain while the atmosphere does all of this instantaneously. These changes just come naturally. 

The only physical law that we need to apply is the conservation of angular momentum. Figure skaters conserve angular momentum all of the time. Their rate of rotation increases as they draw their body inward to a tight spindle. These same skaters slow their rotation by extending their arms and legs outward. 

Shifting inflow winds along the axis of contraction toward the DZ must impact on the shape of that DZ! As I described in “Lines and Swirls in an Unbalanced Atmosphere” a change in any one of the components of the DZ conceptual model, must be communicated to them all.

What happens to the companion swirls that border the veering wind of one of the inflows to the DZ? The cyclonic companion occupies a smaller volume while the area of anticyclonic companion simultaneously expands. I always associated the font size with the intensity or speed of the swirl  rotation. As a result the red “X” must spin faster in the smaller volume and the font size increases. The blue “N” rotates slower in the larger area and the font size decreases. The total amount of angular momentum remains unchanged for the two swirls just like for a figure skater. 

The “backward-S” DZ

The confluent asymptote adjacent to the big spinning red “X” must curl more cyclonically. The confluent asymptote adjacent to the small blue “N” must curl less anticyclonically - which is the same as saying that the confluent asymptote must curl more cyclonically. Both confluent asymptotes must curl more cyclonically relative to their red "X" swirls. Together these two confluent asymptotes are joined at the “col” to construct a single “backward-S” shaped deformation zone. 

Simultaneously the paired swirls across the confluent asymptotes must respond to the changes induced by the veering inflow. As the red X's spin faster in the smaller volumes and become larger fonts, their paired blue N's must spin slower in their enlarged areas and become smaller. There are many different ways to think about this but the result is always the same. 

The end result in a warming wind shear is a double-cyclonic deformation zone.  Both confluent asymptotes stretching outward from the col are shaped cyclonically and the red X's dominate the pattern. Simply, if the cloud lines are shaped by cyclonic swirls, the atmosphere is warming. 

In the northern hemisphere, a double-cyclonic swirl deformation zone must be shaped like a "backward S" which is the term I used in the 1990's when I first started to describe these concepts. South of the equator a double-cyclonic swirl deformation zone is shaped like an "S". I employed these ideas when I was the meteorological support for the Solar Car Race across the Australian Outback in 1996. I was not successful in explaining those concepts then either…

I played these thought experiments in my mind mainly on night shifts. The words played out like a movie in my mind’s eye. The wonderful thing is that the very same show was being played in the satellite loop of the real atmosphere... which was also my forecast concern of the day.

Double-cyclonic Deformation Zone Chain

Here are the take home concepts my weather friends. When do winds veer in the northern hemisphere atmosphere? Warm advection. Where can you find warm advection? When winds blow from the warm southern latitudes toward the pole. In the northern hemisphere that means southerly winds advect warm air toward the north and winds tend to veer with height... and with time. Lines of cloud must be shaped like backward S's or double-cyclonic deformation zones which is the terminology that I prefer. 

In #2065 "Summer Cirrus" (Singleton Lake, Ontario), the long lines of clouds whether they be a gravity wave or a Langmuir streak have a gentle double-cyclonic shape. Use your Coriolis Hand and point your thumb upward for a cyclonic swirl and you can see that the lines of clouds are a chain of double-cyclonic deformation zones as depicted in the above graphic produced by my COMET friends in Boulder, Colorado. The warming wind was over Singleton Lake on that summer day - and that is part of the story behind that painting.  

More on this in the next entry. Keep you paddle in the water and warmest regards... stay safe, 

Phil the Forecaster Chadwick