Lines in the Sky and the Meaning of Life

#2326 "Cirrus Lines" 

I thought it was important to review all of the lines in the sky that we have visited in the past years. Lines are typically more apparent than swirls. Regardless, of which catches your eye, the solution to the weather puzzle must be the same. I keep trying different approaches to better communicate these concepts until one connects with you. Giving up is not an option.

Lines written in the sky are the closest that I can muster to describe the meaning of life in the weather world. Meteorological lines have defined my life for sure. These lines come in only three flavours – gravity waves, deformation zones, and Langmuir. I have written about these many times before but repetition while explaining the concepts from different perspectives might send the message home.

These concepts are best understood from the atmospheric frame of reference moving with the average speed of the atmosphere. Observing the weather with your feet planted on the ground may be our simplest option but please use your imagination to move with the flow. Weather after all is more of a ballet than a battle. 

Gravity waves require two things. 

A stable layer is an inversion in the atmosphere - called such since the potential temperature increases with height versus the typical cooling we observe. Air parcels displaced from a stable layer are returned to the level from which they originated. 

 And a force to cause this displacement and to get the wave going.

Gravity wave lines extend as far as the stable layer and only within the inversion. Waves on a lake can only go as far as the lake. 

The winds in the atmospheric frame of reference are always perpendicular to those gravity waves. Here is an earlier post describing gravity waves - Sunrise or Sunset - Seeing Gravity Wave Clouds. 

Deformation Zones require just one thing!

A puff of wind - a local, relatively stronger wind, is all it takes to generate a deformation zone. A smoke ring swirl is the result of a local wind maximum. The swirls create a three-dimensional “skin” that is a 3-D boundary between the puff of wind and the nearby undisturbed fluid. 

Deformation zone “skins” are as large as the swirls created by the local wind maximum. They extend through the depths of the atmosphere with vertical vortices. 

A linear deformation zone is a quasi-horizontal intersection between the skin and a layer of moisture that makes the movement of the air visible. These linear deformation zone patterns occur with every stroke of the paddle on a lake. 

 The winds in the atmospheric frame of reference are always perpendicular to the col in the deformation zone pattern.  I have written about deformation zones so many times that it is difficult to select just one link. The following explains the three-dimensional aspects of the deformation skin without any math - Down to Earth Meteorology. 

Langmuir Streaks require two things. 

In contrast with gravity waves, Langmuir streets require an unstable layer in the atmosphere. An unstable layer is where the potential temperature decreases with height. Air parcels displaced from their level keep going until they encounter warmer air and a stable layer. The depth of this unstable layer should not be too deep for effective and obvious Langmuir Streaks. 

Langmuir Streaks also require wind. The vertical circulations within the unstable layer are stretched along the wind direction into elongated, helical flows. 

Neighbouring Langmuir Streaks interact to create bands of ascent that in turn separate lines of descent. 

The unstable layers are most common within the planetary boundary layer where the atmosphere is often heated from below causing air parcels to rise. Unstable layers can also be found within the free atmosphere, most notably below the tropopause.  

Langmuir Streaks can be witnessed as long lines of relatively calm water bordering rippled surfaces when a wind crosses a lake. The mean wind direction (in the atmospheric frame of reference) through the depth of the Langmuir Streaks parallels the cloud lines. 

Langmuir Streaks have long been a favourite subject. Here is one blog that describes more of the history as well - Langmuir Streaks – Take the time to Observe and Learn from Nature. 

I witnessed these three-line flavours found in fluids as a canoeist long before I became a meteorologist. It was important to read the lake so that you could understand the wind. Knowing the breeze informs you how to paddle your canoe. 

My lake transformed into the atmosphere when I became a meteorologist in 1977. Satellite imagery became available shortly thereafter. Oh my... the new satellite data displayed the real world which up to then, I had been trying to comprehend mainly through mathematics. 

The atmosphere was just like my lake! This new data displayed gravity waves everywhere and they accurately revealed the direction of the wind within the cloud at that level… within the atmospheric frame of reference. The gravity waves also revealed that there was a stable layer. 

The science of deformation zones followed in the early 1980s with the inspirational work of Roger Weldon. A single deformation zone revealed the location of four correlated swirls, the col, two opposing pairs of companion circulations, and the two confluent asymptotes. One could diagnose the complete weather pattern from a single line. And it was the real weather and not a numerical simulation.

The lake and atmospheric deformation zones - both are fluids. 

Langmuir Streaks became more important in the late 1980s when the prediction of snow squalls off the Great Lakes became a very big part of my meteorological effort.  

I did a lot of hand waving in those early days. A precise explanation and solution of these lines required a lot of mathematics. The math didn’t significantly augment the understanding gained from simply watching the satellite imagery. By the early 1990s, we even had terrific animations of satellite images which was a huge leap forward from the preliminary Walt Disney "cartooning" of still images, followed by the video tape filming of those hard copy satellite pictures. 

Gravity waves, deformation zones and Langmuir Streaks were everywhere within satellite imagery and with animation, we could watch them move and develop.  The dynamic lines in the rapidly improving satellite imagery were real and we just had to discover what they meant. It was an exciting time in meteorology. I loved my profession... 

The frame of reference from which we observe these lines is vital. I often failed to explain the difference. The wind observed by the observing network of the Atmospheric Environment Service was the vector addition of that atmosphere frame wind and the mean speed that the atmosphere was moving with respect to the earth. The two are nearly the same where the atmosphere is stagnant but quite different if the weather systems are moving quickly across the landscape. 

The entire weather service was tied to the earth frame of reference. The rapidly evolving science of numerical simulations of the atmosphere - Numerical Weather Prediction (NWP) came to my rescue. The lines of absolute vorticity best matched the atmospheric frame winds that I was observing in the lines revealed in the satellite imagery! Absolute vorticity will not be on the quiz. 

Looking northeast across North America using the
3-Dimensional Water Vapour Imagery

It is important to note that initially I was reliant on clouds as tracers for the atmospheric frame winds... then along came my new best friend... water vapour imagery. Water vapour was everywhere within the atmospheric ocean... My prayers had been answered. 

The wind in the atmospheric frame of reference sculpts the water vapour into three-dimensional shapes that really reveal the weather. The water vapour data can even be displayed in 3-D - something we achieved at COMET in 2009. There was a lot more hand-waving to do with 3-D Water Vapour Imagery but alas, it didn't catch on either. 

Lines in the atmosphere have to be either gravity waves, deformation zones or Langmuir Streaks. Using these lines as witnessed in the satellite imagery reveals the fundamental meteorological forces at play in the atmosphere… and thus the weather. I learned those lessons from the atmosphere and tried to explain what they meant first to myself and then to anyone who would listen. I tried various approaches and analogies to find one that would connect. I am still trying.

A Typical Sunset with Many Lines in the Sky
I did not label them all ... they all tell a story. 

The story of lines in fluids has been the meaning of life for me... both from the stern of the canoe and the swivel chair of the Severe Weather Desk. Life was and  is good.

Here are some blogs from that might be of assistance. 

Weather Watching Guide for Everyone… looking at the very same concepts in a slightly different way. 

Weather Watching Guide - Contrails described the man-made lines in the sky which I did not touch on here. 

In Enhancing the Satellite View of the Atmosphere I described some of my efforts to glean all of the meteorological information out of the satellite data. To find something, you have to start by looking. 

The next Blog will summarize where to look for the different flavours of these lines in the sky. From a weather perspective, it is beneficial to examine the "warm sector lake" portion of the atmospheric ocean.

Warmest regards and keep your paddle in the water,

Phil Chadwick