The Theory of Unified Swirls

#1717 "Sunset Waves Nite" Pixels Link

Every profession has its own jargon but I will try to refrain from the practice. Swirls are call vorticity by meteorologists. A swirl is simply a rotation. In the second post of this series I explained that Rotation is the Key to Unlock Cloud Shapes. In the third post Cloud Shapes from Rotation, I described how cyclonic rotation shapes clouds. The moisture patterns that result tell you about the nature of the swirl itself.

Everything is simpler from the atmospheric point of view.  We may not live in the clouds and the atmospheric frame of reference but we can imagine. I am about to make cloud swirls and shapes even simpler and the answer was blowing in the wind all of the time. I hinted at the meaning of life in the very first post Cloud Shapes and Lines in the Atmosphere and to some, what follows may be life changing. You will be able to view clouds from both sides now just like Joni (Mitchell).

I will credit Bob Dylan with this discovery even though he was just blowing smoke. Here Bob is blowing a substandard smoke ring but it is the thought that counts.

Smoke rings are created from a quick puff of wind, near circular lips and some tracer to reveal the resultant air circulations. I am not a smoker so have never done this first hand. The puff of wind creates speed shear. Speed shear must move in the earth frame of reference which is why smoke rings are never stationary. In a flat display, meteorologists could analyze a smoke ring cross-section as follows below.

Looking in the direction of the puff, the speed shear must create a cyclonic swirl to the left and a complimentary, companion anticyclonic swirl to the right. Cyclonic rotation is associated with upward motion in the atmosphere. Anticyclonic rotation is a downer. The illustrated right hand rule will help you remember up and down. Meteorologists have treated cyclonic and anticyclonic swirls as different entities. They are not. Let me explain...

First let’s talk about the atmosphere. The atmosphere as pictured is relatively shallow. The atmosphere has a thickness comparable to the skin of an apple - more or less. Actually 99% of the atmosphere is found within 30 km of the earth’s surface. The earth’s radius is about 6400 km so the atmospheric layer is only 0.5% of the earth’s radius. That’s shallow! 

Early meteorologists concentrated on the horizontal motions in the atmosphere. Our observations were only from the surface. The paper weather maps were flat. That is all we had. How can anything so flat have any important three dimensional patterns? These concepts have led to the separation between cyclonic and anticyclonic swirls. In fact,the interesting part of weather and meteorology occurs in the vertical and we can learn from that smoke ring.

A smoke ring is simply a puff of wind and it is a three dimensional circle of spin. If we look along the same direction as the puff of wind and follow the smoke ring with our right thumb we see that both cyclonic and anticyclonic spin can be found along the same smoke ring. Meteorological convention has just separated this single, simple physical phenomena into two separate branches through only considering the horizontal cross-section. The smoke or moisture patterns across the ring are mirror reflections of each other. The smoker has learned to concentrate the smoke into tightly wound vortices.  All one needs is a puff of breath and practice.

The smoke ring and swirls are larger and stronger with a stronger increase in the speed of the puff. As the vorticity maximum or swirl to the left of the straight line puff increases, the vorticity minimum must also increase correspondingly. I called these companion circulations – what happens to one swirl must also happen to its buddy swirl. Swirls also need closure – either back on itself or on a surface. That’s just the way it is… more on this in another post.

The take home message is to remember the smoke ring in the atmospheric frame of reference. Always envision a three dimensional ring even though the flat paper might can only depict cyclonic and anticyclonic swirls. To really understand the atmosphere we need to remain in the three dimensional atmospheric frame. In the atmospheric frame, everything is much simpler to understand. A smoke ring is just one half of the deformation zone conceptual model illustrated in the very first post Cloud Shapes and Lines in the Atmosphere.
And that is how you can make a line out of rotation....

In 1985 when I started teaching this in the Training Branch of Environment Canada, I tried different approaches and diverse graphics to try to connect with the students. Everyone learns differently. I may have failed but I never gave up. Sooner or later, one of these attempts would work and open the atmospheric world to them.

I spent a lot of time thinking about and painting clouds to come up with these simple truths. Sometimes the simplest things are the hardest to imagine. Maybe I was trying too hard and over-complicating things. Maybe I was just slow…

There is more to come...

Phil the Forecaster