Empathetic Meteorology

#1714 "White Pine Island"
Cloud Patterns within the Atmospheric Frame of Reference
and what they mean

Empathy is important. It is vital to examine a process from the appropriate point of view in order for it to make the most sense. Humans are anthropocentric by nature - which is very unnatural! Ask Copernicus and Galileo about the challenges they faced - great minds who dared to think outside the proverbial box encountering obstacles beyond belief. 

Copernicus developed heliocentrism in 1514 that the Sun and not the Earth was the centre of the "Universe". It was published the year he died. Galileo Galilei (1564-1642) the father of modern science, agreed with Copernicus. Galileo was convicted of “vehement suspicion of heresy” and under threat of torture from the Church. Galileo was forced to express sorrow and to curse his errors .. but I digress... 

Meteorology in Canada flourished out of a necessity for safer air travel - simply to avoid storms. Aviation requires a frame of reference attached to the airports and constant pressure surfaces. A fluid on a rotating, oblate spheroid like the Earth does not care much about any of that. Fluids can be better understood following an empathetic frame of reference moving with the fluid. 

Air parcels follow constant energy surfaces (isentropic surfaces) fuelled by contrasting temperatures between the equator and the poles (see "The Jet Stream - The Bind that Ties"). The average westerly winds of the jet streams in both hemispheres move the storms along but what shapes those patterns? The answer is indeed blowing in the wind and using a frame of reference attached to the storm. 

The purple local wind maximum spins up two, adjacent
 companion swirls

A puff of stronger wind (local maximum in the jet stream and the purple vector in the accompanying graphic) creates two paired vortices. The so-called "cyclonic"  or vorticity maximum (red X) is poleward of the jet maximum (in the northern hemisphere to the left looking downstream). By meteorological convention, the "anticyclonic" or vorticity minimum (blue N) is equatorward of the jet maximum (to the right looking downstream in the northern hemisphere). Use your Coriolis Hand to visualize these paired rotations - your right hand for the Northern Hemisphere and the left hand for Down-under.  

These paired circulations are simply cross-sections through the three-dimensional smoke ring blown by the local jet maximum but this blog is more about the patterns caused by the rotational swirls as viewed in the empathetic, atmospheric frame of reference. (See "What do Smoke Rings have to do with Croquet?" for the three-dimensional  approach)

The shape of the moisture patterns is determined by simple vector addition: 

• the relative strength of the local wind maximum which determines the rate of rotation of the accompanying swirls; and
• the speed at which the swirls are being translated along by the jet stream.

I did this work on a night shift sometime in the early 1980s. I saw a pattern in the newly available satellite imagery and simply asked "why?" The real atmosphere was the best teacher I could have hoped for. 

The following graphics are the same for whatever speed we wish to assign to the local wind maximum. The associated weather is of course more intense with the stronger jets. 

In "Rotation is the Key to Unlock Cloud Shapes" I explained how the cyclonic swirl in the atmospheric frame of reference formed an open trough in the Earth Frame. 

The open trough became deeper as either the cyclonic swirl (green vectors within the green box) increased in speed or the speed of translation of the system decreased (purple vector attached to the purple circle). Open troughs generally move quickly and are not associated with surface low-pressure areas - both observations relative to the Earth frame. Open troughs typically produce clouds in the free atmosphere but no precipitation. 

When the vectors of the rotational swirl match the 
translational vector, an incipient low is about to
form in the Earth frame of reference -
the same low-pressure area that
meteorologists analyse on weather maps. 

As the speed of the swirl increases more that the speed of system translation, the location of the low on the weather map shifts in the direction of Coriolis Deflection (to the right in the northern hemisphere). In those situations when the system translational speed reduces to zero, the low in the Earth frame of reference must be collocated with the cyclonic swirl in the atmospheric frame.

The clincher is that the centre of the swirl in the atmospheric frame of reference is exactly the centre of the moisture swirl that we witness in satellite imagery - and that is the relative vorticity centre using meteorologist lingo. That is what I discovered on that night shift while closely examining the grainy, hard-copy infrared satellite image. It was a eureka moment for me that would define most of my meteorological life. 

The swirls in the satellite imagery could be analyzed as vorticity centres. Vorticity centres were a staple of the products found in numerical simulations of the atmosphere. Comparing the location of the vorticity centres in the real atmosphere with those in the numerical, simulated atmosphere could lead to improved predictions especially when strong vortices were involved. 

It was really that simple. My goal was to teach this at Training Branch back in the mid-1980s. I was not successful then but did have some success eventually in Boulder, Colorado at COMET. Some of this work can be found within the COMET online material and it is all free - so the price is very right. I have reproduced some of that material in these blogs because it is so very important in order to understand cloud shapes. See "Cloud Shapes from Rotation" for more on this. The additional influence of wind shear that spins up swirls is required to make a cusp in the cloud formation. 

The identical process can be described for the anticyclonic swirls. 

Open anticyclonic ridge - fast-moving fair weather

Incipient High in the Earth frame of reference when the rotational
speed of the anticyclonic swirl is the same as the speed of translation

The location of the high-pressure centre shifts in the anti-
Coriolis Deflection direction (to the left in the northern
hemisphere) as the speed of translation diminishes
to zero and the high-pressure centre analyzed on the
weather map in the Earth frame of reference is collocated
with the anticyclonic swirl.

Clouds make so much more sense if we use an empathetic eye and watch them from the atmospheric frame of reference. Cloud lines and patterns shaped by the swirls can be easily understood.

The red “X” is considered to be positive or cyclonic (counter-clockwise in the northern hemisphere) rotation of the atmosphere. The resultant cloud edges are actually two cyclonically curved arcs that meet smoothly at the centre of rotation. Pointing your right thumb upward at an “X” also points your fingers in the direction of the cyclonic rotation of the atmosphere.

The following animations might assist you to unlock the door of understanding for you...

The point of inflection is not smooth but becomes a cusp when speed shear rotation is added into the mix. In the following animations, the red X of the vorticity centre is between the two components of pure rotation "R" and shear "S". Both rotation and shear cause the atmosphere to swirl. 

As the wind shear component "S" increases, the sharpness of the cusp increases correspondingly. 

If you practice this just a few times and take the opportunity to watch clouds develop and move, you will quickly begin to understand cyclonic cloud shapes. Follow the cloud edges cyclonically to the cusp where the curvature of the arc changes. The cusp is your centre of rotation; the relative vorticity centre; the swirl and where you begin your empathetic view of the atmospheric moisture.

Exactly the same can be done for so-called anticyclonic circulations except that everything is mirrored in reverse.  Anticyclonic circulations are typically associated with descending air and thus fewer clouds- but the weather is still very important. 

Looking back, this work on the centre of swirls seems intuitively obvious. At the time, it was anything but and the challenges were many and varied. A background in art certainly was beneficial to visualize the atmospheric motions from its frame of reference. In the early 1990s with vastly improved satellite imagery,  I attempted to translate that data with the mean translation. The goal of "King Atmosphere Relative Display" or KARD was to further prove the concepts and assist others to see the bumper car aspects of atmospheric interactions. Some of the effort was completed at the King Radar site near Watershed Farm but again the challenges were large and  I had to resort to hand waving.  

I did so much hand-waving in my time that it became more like bad break-dancing. I never tired of attempting to explain the beauty and simplicity of the weather. I guess I have yet to stop trying as I still empathically have my mind up in the clouds within their frame of reference. I also have more time now to take my paints along with me for the ride. 

There is much more that I could explain but this is enough for now. I hope you can get outside with your Coriolis Hand and watch the clouds go by and appreciate them even more... 

Warmest regards and keep your paddle in the water,

Phil Chadwick