The changes in color represent changes in altitude as measured for one specific air pressure level, 500 mb, which is about half of the pressure at sea level. As the altitude of 500 mb changes gradients are set up, faintly displayed on the map as isobars, like those seen at surface pressures except that here everything is recorded in a 3D mode. A key point is that upper level winds follow exactly along courses set by the isobars, always in an easterly direction, around and around the central pole. Another key point—the winds tend to be stiffest on certain specific courses, three in particular. One of these tracks follows along the outer edge of the light blue ring you can see. Another tracks the outer edge of the green ring, which is a little broader and more scrambled in places. The third follows the broad edge where the light reddish tone becomes dark, with still more irregularities and maybe a bit weaker. Whenever two of these tracks come close together, allowing these speedy winds to merge, their combined speeds tend to reinforce each other by accelerating, which can be observed in a prominent way as found on the Jetstream map.
Today I want to focus mainly on the light blue ring, which is totally encompassed by its own lane for sturdy winds to track, because those winds are sturdy enough to largely block the efforts of any winds approaching from the outside to enter into any part of the sizeable area that lies within the light blue perimeter. Those outside winds are often carriers of unusual amounts of water vapor, and they are generally heading in a direction leading toward the pole, but on this map we see them being partly or completely blocked from crossing a border corresponding to the light blue ring in the map above. (The thin white line you can see is fairly similar to the shape of the blue ring.)
The first thing to notice is that nearly all of the darkest gray and black, having a Pwat value mostly below 4 kg plus a lesser amount above, falls within the same area as that of the light blue ring above. You can also see how a number of movements of currents of wind having higher Pwat values are held back from penetrating, including a few that look much more aggressive than others. It’s as if the blue zone has set up a line of defense for some reason. That in itself is a big story, but there is more, and this part is so extraordinary that I could not let it pass beyond today without recording. Look closely at the shades of Pwat that lie within the blue zone and you see a remarkable degree of uniformity that run from the US Upper Midwest all the way through Canada and into the heart of the still-frozen Arctic Ocean. It has all been kind of mixed into one big pool, as if whatever was there before had been put through a blender, leaving it oblivious to the effects of sunshine, or latitude, or any other such sort of thing. The result, as we see here, is a variety of major temperature anomalies:
The range we are seeing, from -10C in the southern part to +15-18C in the north, mostly tied to a very tight spread of Pwat values around 2-5 kg, is a roundabout way of telling us that “normal” Pwat values on this date would range from less than 2 in the north to around 10 in the south. Today, with everything mixed together, those values have been doubled in some of these places, halved or less in others. I regret that there is no record available for what is precisely normal in all these places, but estimating, with practice, is not terribly difficult. Again, what is so interesting is the unusual amount of Pwat uniformity that has been achieved within the large confines of the blue zone. Things will soon be changing, since today’s blue zone is sure to look quite different in size and shape in the near future, and probably still more different in the far-off future. You are invited to do a quick map study just like this at both poles on any or every day, using “live” daily maps, to check out the ongoing consistency of the relationships we are now seeing.
Carl