Part 2 of Carl’s theory describes the mechanism that facilitates the poleward movement of precipitable water (PW) in the upper level of the atmosphere. All PW enters this zone in the form of steadily flowing streams of water vapor that originate in surface waters (or by transpiration) along the borders of the tropical belt. The stream contents must stay in motion in order to survive. Being jammed up or completely stopped quickly leads to life-shortening precipitation. The motion itself has a directional bias, in the form of a pronounced tendency of poleward migration, applicable to all PW concentrations as long as they remain active. The progress of every particular act of migration is primarily determined by the nature of prevailing local wind activity, which is subject to unique trends of variability. Today’s letter will focus on images of the current status of critical factors that regularly impose their combined effect on wind patterns that unfold in the upper level of the NH atmosphere. It all begins with the actual status of surface air temperatures:
As described in previous letters, these temperatures have a direct effect on the configuration of upper-level air pressure differentials, mainly transmitted by upward pressures that are dependent on varying thermal expansion rates of the air at the surface. The blue zone in the configuration map represents the imprint created from below by subfreezing surface temperatures; the green zone by temperatures in the range of zero to about 10C. (Land surfaces tend to be more accurate than oceans in the transmission of this effect.) Everything above 10C ends up in the red zone.
These map shadings provide us with a very helpful guide to the positioning and strength of major jetstream pathways and the winds they carry, as expressed daily in the upper atmosphere. Three such pathways demand most of our attention. The innermost of these, now nearly defunct, surrounds the perimeter of the blue zone. The next pathway is located on or near the perimeter of the green zone. On close examination, I think the most apt description of its location shows it splitting into a secondary fit with the more darkly-shaded green track that always runs just inside the lighter green perimeter. The snake-like meandering of this track gives the stream a bit of extra play-action. The third major pathway is found well to the inside of the red zone, along the line where light and dark red shades are adjacent and in sharp contrast. All three of these pathways can be traced out at any time by doing daily map comparisons. In some places the winds may disappear but isobars still reveal the location of the pathway:
What I have learned is that the blue zone and green zone pathways are the most efficient at blocking the migration of PW concentrations, setting up barriers that are difficult to cross. Wind velocities always make critical differences in their effectiveness. Jet winds on the red zone pathway, regardless of velocity, tend to function more as carriers of PW rather than barriers. Their carrying motion is mainly from west to east, which is only a minor hindrance to poleward migration. Large concentrations of PW regularly manage to cross over to the pole side of these winds and continue on in the more favored way. Today’s result has all the earmarks:
The area covered by the green zone has indeed been kept fairly clear of PW intrusions, with one exception—the mass moving directly into the polar zone from northwestern Canada. When you look closely at the air pressure map you can easily pick out the weakness inside the green zone that is allowing this to happen. The weakness was there in the first place because of warmer than usual surface temperatures already present in that area, as depicted by the temperature map at the top. That warm area will be intensifying today because of its exposure to the high level of greenhouse energy now being provided by the incoming PW stream. As it intensifies it will deepen its imprint on high-altitude air pressure differentials. That’s how self-reinforcing feedback loops extend themselves. This rupture in the green zone could soon cause it to split into two pieces, by kinking to a smaller rupture can be seen emerging on the opposite side. Each new piece will have its own perimeter jetstream pathway, both of them more penetrable than the one we now see.
Carl