Today I want to focus on the map showing high-altitude air pressure configuration (HAPC), which I’m sure is everybody’s favorite. This is what I consider the key component of current weather systems and just as importantly, perhaps also a key component of future climate change. The configuration is divided into two distinct parts that are of prominence, one in the north and one in the south. Comparing the two, and their actual observed influence on each hemisphere, will explain why they are so important Recently the comparisons have been at an extreme and today is perhaps more so than ever, so let’s bring up a global map:
Never mind what you see within the tropical belt, just focus on the sections of the two hemispheric caps that are dominated by the green and blue shading. That’s where the action is, and there is plenty to see, but only in the north. The shape of each HAPC is the critical feature for comparison, and the two shapes could not be more different at this time of year—the wintry north should in fact now be the one having the more compact shape of the two. Configuration shape is what always sets up the pathways on which critically important jetstream winds naturally develop. The positioning and regularity of these pathways will go on to fully determine the location and relative strength of all the winds they contain. One kind of pathway always sets up wherever you see the outer edges of the blue zone, or zones in this case; the other on the outer fringe of wherever the green zone is in view. Here is the result for today:
Some extraordinary information can be gleaned from these two maps. Because of the extraordinary way the shapes of the blue and green zones have formed, the total mileage of pathway formation available for jetstream winds to take effect is far greater in the north than in the south. We accordingly can see a lot more streams, and more crowded as well. It also appears that the outer edges of the green zone are not limited to places where green meets red. In some tight fitting situations green on one side of blue is cramped up against green on another side of blue, allowing parallel green pathways that are both functional. Along with all the twists and turns that are in evidence, the end result is a completely different pattern of jetstream activity from the pattern in the south. This situation should then translate into considerable differences in the way high-altitude steams of precipitable water (PW) are distributed as they proceed on their normal courses of poleward movement:
Details of PW movement do not show up as clearly on this map as on the regional maps, and I won’t try to describe the differences today, but they are strong. The main point to make is that when there is such an excessive amount of jetstream activity, and so scrambled in placement, the result is sure to have relatively (for the season) large concentrations of PW running wild in places where they normally would not be found at this time of year. When such is the case, given the regular relationship between PW and surface temperatures, a further consequence should be the appearance of a profusion of strong temperature anomalies at the surface, both cold and warm, just because of so much abnormality of where PW is flowing:
In the south, where the entire situation is just the opposite,strong anomalies are hard to find, and could very well stay that way for this reason: The HAPC images in each hemisphere are in a constant state of slow rotation from west to east. When you look at how the south is now set up on each of these images there is no reason to expect much change, because of the orderly and repetitive manner in which everything lines up horizontally. In the north, where there is no such order, rotation will bring a constant flow of changes, with new developments just as likely to be abnormal as those currently in place. Are there any long-term implications? That must remain as a subject for future discussion.
Carl