The Jet Stream - The Bind that Ties

#1061 "Windy St Lawrence" Pixels Link

The dry conveyor belt is intrinsically tied to the warm conveyor belt by the jet stream. In the early years I used the longer phrase “axis of maximum winds” as a general term to describe the wind that was shaping the satellite patterns. The unusual shapes that I was trying to describe and understand on those grainy early 1980 satellite images did not match the Venn Diagrams that we were taught in the Training Branch of the Atmospheric Environmental Service. Those early meteorological cookbooks tried to simplify techniques to better forecast the weather . This was before before computer simulations of the atmosphere really started to improve. The location and characteristics of the jet stream was the number one priority to better prediction of the weather.

A PowerPoint Screen from my Teaching Days
with COMET, NOMEK and EUMETSAT

There were four basic ingredients in the jet stream menu.
• Find the dry slot in the comma pattern
• Baroclinic zone cirrus streaks
• Low cloud discontinuities
• Connect the dots located above.

The strongest winds or the jet maxima (the J in the accompanying graphic) were located in the dry slot and downstream from the col.

Using the new tool of satellite imagery and these simple ingredients led to more discoveries. The conveyor belt conceptual model was the first and foremost among those.

The Weather Machine Cogs or Swirls lay down
three dimensional deformation zone skins
 that encapsulate the weather. 

The jet stream is like the broad leather belt in the conveyor belt machine wrapped around the drive wheels of the weather engine. The axis of maximum winds spins up the cyclonic tube of the smoke ring in the trough. The jet then ascends the ridge to spin the anticyclonic tube before exiting into the next system downstream. The jet stream or axis of maximum winds powers and ties the cogs of the dry conveyor belt to those of the warm conveyor belt. If you really want to learn about a system, you need to follow the energy….

I always found it important to go back to first principles to explain how the mid latitude storms were fueled. All of the energy must ultimately come from the sun and this energy needs to be moved around the Globe to keep everything in balance. Every closed system must find its balance. 

Zonal Jet Stream

The sun heats the darker earth tones of the lower altitudes. Those surfaces are nearly perpendicular to the sun’s rays through most of the year. At higher latitudes the earth surfaces are more likely to be covered by reflective snow and ice. The inclined surfaces receive only a glancing exposure to the sun’s rays. The poles do not soak in nearly as much heat energy as the equatorial regions. 

The zonal jet stream results from the temperature difference between the equator and the poles. The jet stream blows from west to east. This thermal wind direction is easy to remember. If you keep your right hand in the warm air and your left hand in the cold air, you are looking in the direction of the wind caused by the contrasting temperature. 

Increasingly Meridional Jet Stream

This zonal jet does not move heat energy around. Weather happens as the jet stream becomes more meridional.  Typically the storms become stronger and slower moving as the jet stream flows increasingly meridional as it plunges southward around deep troughs before rising downstream around the large upper ridge. 

The conveyor belt conceptual model explains how warm air is moved northward and cold air to the south and how meridional flows relate to the weather. 

There is another important source of energy. The energy in the water cycle also comes from the sun. Water evaporated from the earth requires the heat of vapourization to change from a liquid to a gas. The heat of sublimation is needed for a solid to change to the vapour phase. The conveyor belts move water in all of its forms around the globe. The energy inherent in the phases of water moves with those winds as well. 

White and dark blue bubbles on this Canada Day Water Vapour
image are convective bubbles rising off the isentropic surfaces

Water vapour rises in the isentropic ascending flow of the warm conveyor belt. The vapour cools and at some point returns back to either a liquid (rain) or solid form (snow) with the release of that heat energy back into the atmosphere. Those air parcels where the precipitation is created from the vapour, are suddenly heated and they explode off the constant energy surface of the isentrope. These warmed parcels rise like hot air balloons to much higher potential temperature surfaces in the atmosphere. Meteorologists call these ascending air parcels convectively unstable. The release of energy from the change of state fuels the cyclonic swirl, the warm conveyor belt, the precipitation and the vertical convection. Water vapour imagery dramatically reveals those parcels convectively leaving the isentropic surfaces. 

A similar but opposite process can occur in the dry conveyor. Any liquid or solid phase water within the dry conveyor belt can cool air parcels containing them as they vapourize to a gaseous phase. The bubbles of parcels of cooled gaseous water vapour can sink like the proverbially lead balloon. You can feel these cold parcels of air under virga. Evapourating rain drops cool those bubbles of air often before a few of them actually succeed in reaching the ground thus creating a shower. 

The following animation from Canada Day reveals the wealth of meteorological information that may be gleaned from the relative motions of the warm and dry conveyor belts - that is the real weather. 

These are the big energy sources that fuel the conveyor belt conceptual model and mid latitude weather and storms. This energy all comes from the sun... and it happens in an exceedingly thin atmosphere about a twentieth of the thickness of the skin of an apple if an apple was the size of the earth... 

That's enough for today... but it ties the dry and warm conveyor belts together and binds it with the energy from the sun... and yes, I am dyslexic ...

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick