The Main Veil of the Weather Dance - The Warm Conveyor Belt

2218 "Sunset Concert in AC and CI" Pixels Link

Warm Conveyor Belt - WCB in Red 

The warm conveyor belt (marked WCB in the figure as the red flow) represents the main source of warm, moist air that feeds the cyclone. Heat and moisture are energy for the development of the low pressure area. The warm conveyor belt originates in the warm sector of the cyclone far to the south and flows poleward roughly parallel to and ahead of the cold front – rising as it travels northward for free on the isentropic surfaces.  (See "Isentropic Surfaces - Science and Art Merges") This layer can be 5000 feet deep and typically begins in the convective mixing layer far to the south well away from the low center. As the flow approaches the warm front, it continues to ascend with its strongest rise over and north of the warm front. This is the area of strongest warm air advection.

The leading edge of the warm conveyor belt is the deformation zone (see “A Closer Look at Lines in the Sky”) The flow splits at the col. Looking downstream to the right of the col, the flow turns anticyclonically or clockwise as it joins the jet level flow in the upper troposphere. Placing the fingers of your right hand in the direction of the curl must point your thumb downward. This is the anticyclonic vorticity centre of the deformation zone and it links to a high pressure circulation at the surface.

Looking upstream to the left of the col, the flow starts to turn cyclonically or counter-clockwise as it wraps around the low pressure area and the cyclonic circulation. Placing the fingers of your right hand in the direction of the swirl must point for thumb upward. This is the cyclonic vorticity centre of the deformation zone and see how it links to the low at the surface. This was described in blog “Rotation is the Key to Unlock Cloud Shapes”.

Together the companion anticyclonic and cyclonic swirls link in three dimensions into one large smoke ring in the sky. The was described in the "The Theory of Unified Swirls" using Bob Dylan's smoke ring to explain the circulations in a fluid. Similarly the companion swirl centres associated with each deformation zone that describes a smoke ring, are also three dimensional. These vorticity tubes extend in the vertical reaching right down to the ground near the warm front. The smoke ring morphs into a Croquet hoop at the warm front as well - more on that later.

My view for painting 2218 "Sunset Concert in AC and CI"

In addition the deformation zone is three dimensional! The deformation zone line is just where the deformation zone veil that encloses the warm and moist air mass, intersects with an isentropic energy level. If we take a cross-section along the warm conveyor belt we can see air parcels of different potential energy following the isentropic surfaces on their free ride northward.

The ingestion of air into the engine of the cyclone takes place over days as the system grows in size and energy. Some of these air sources will be more moist than others. In the absence of convective instability, these different air sources will find their assigned energy level in the isentropic conveyor belt and gently rise as they move northward. Layers of moisture will often remain separated from each other.

The warmest potential temperature air is highest in the atmosphere. The leading edge of this moisture creates the highest deformation zone and leads to the phrase "cirrostratus coming at us". The next warmest potential temperature air is likely to be in the middle levels of the atmosphere and bring altostratus northward but not as far north as the cirrus. The lowest layer of air comprising the warm conveyor belt creates another deformation zone enclosing nimbostratus.

Connecting all of these deformation zones into a deformation skin or veil encloses the leading edge of the warm conveyor belt. It takes about 4000 feet of cloud depth to start precipitation processes. Typically that means it takes all three layers of cloud so that precipitation starts after the lowest level deformation zone passes by.

Looking East just before sunrise - North to the left

Seeing is believing and I have been witnessing this process since I was a teenager and sometimes lucky enough to have a camera or a paint brush handy. Here are just a few.

Looking east at sunrise

Looking west from the Oak Ridges Moraine at sunset

So this is the beautiful warm conveyor belt that brings heat and moisture northward as part of the energy balance of the earth. It is one of the dancers in every cyclone that makes weather more of a ballet than a battle. There is much more to know but I will save that for another entry or two.

Warmest regards,
Phil the Forecaster

PS: Much more to come and thank you to my COMET friends in Boulder who helped publish this stuff.