We have looked at the current configuration of high-altitude air preesure in detail at each of the two polar zones, with a focus on the blue-shaded zones in each hemisphere. We noted how the borders of each of the two blue zones bear a relationship with the borders of regions on the surface directly below where average temperatures for the most part were either below freezing or just a degree or two above. We have also noted how the green-shaded zone that surrounds the blue zone generally extends over surface territory that is roughly five or six degrees warmer. Everything in the center of the map is warmer yet, and covered by the red zone. Let’s put all of this into a global perspective on the two relevant maps, starting with air pressure:
The significant current differences in total construction and areas of coverage of the two blue zones, while badly distorted in this imagery, really stand out. The same can be said about the green zones, in that the one in the north is unable to maintain an even distance of separation from the nearby blue zone comparable to the pairing in the south. (This will be seen later on to have an important side effect on jetstream activity.) The red zone is a blend that divides two parts, one lightly shaded and one darker. The two lighter sections both tend to participate in the distinctive activities of the mid-to-upper latitudes of each hemisphere. The dark part generally corresponds with the planet’s tropical zone, which is of singular construction and has its own unique patterns of seasonality and various other, mostly moderate, sources of difference. Here are the current temperatures we are getting from the entire combination of zones. Together, the two maps basically establish an obvious overall relationship between variations in high-altitude air pressure differentials and the hot-to-cold spread of surface air temperatures, about three miles lower down:
Now for the global jetstream map, which is clearly divided into similar zones of separation. The tropics have sporadic accelerated winds which show up on the map but are of no particular consequence. Each hemisphere shares the same basic pattern, but each of the patterns incorporates a sequence of completely separate activation and consequences. These consequences, which are typically not set on the same scale, can be seen to have significant importance with respect to hemispheric variations in both weather and climate.
Basic to both hemispheres, jetstream winds are carried by three major pathways that normally make a continuous circle around the globe. The locations of these pathways are set by nature, keyed to dependence on air pressure differentials. Remarkably, the three shaded zones on the map, blue, green and red, provide an accurate guide to the immediate location of these pathways, well-tuned to a timely updating of all the daily changes.
One pathway, the innermost, follows a track marked by the light blue line on the border of the blue zone. Another major is set along the outer border of the green zone. The outermost pathway is set up on the outside border of the light red zone, just before it separates from the darker red that marks the beginning of the tropical belt. Minor versions of all three pathways take effect when fragments break off from any of the three large zones of normally consistent temperature spreads, which is not uncommon. Other features, all of whch have been previously described, will be summarized again in a future letter.
Carl