The Climate Letter archive from last year holds an image of high-altitude air pressure configuration on April 15 that I will show here so it can be compared side by side with the one for today. They are both in a state of accelerated transition from winter to summer, and I can see little difference in the overall amount of deterioration up to this date:
I do think the total perimeter of the blue zone is a little shorter this year, and the same may be true of the “inner perimeter” of the green zone that remains in place when there are separations. More comparisons of these particular maps should be of interest as summer progresses and will become available in the weeks to come. The coordinated archiving of many kinds of map images for future viewing is now a primary objective of these letters.
With this last image as a reference, we have an opportunity to throw some light on how jetstream pathways are set up and what happens to the winds they contain when pathways become twisted and scrambled, as they certainly are right now. The view for today:
In order to visualize the pathway locations one should give primary consideration to isobar lines that are in place rather than just wind speed imagery. The actual wind speed that exists along any one pathway tends to be highly variable, sometimes moving too slow for imaging. In general, speediness should be thought of as mostly an effect created by the relative proximity of separate primary pathways, blue, green and red. Closeness, over any distance, is sure to produce the highest of all speeds due to mutual acceleration. Other than that, speeds on a more isolated pathway often tend to be ramped up when a reasonably straight course continues that way over a considerable distance. As soon as there is a sharper type of bend the speed will be slowed, and in some cases, especially in the red zone, the path may even be split into two or more pieces.
The red zone pathway is problematic in another way, because its location is not quite as dependable as those of the blue and green zone pathways, and also more prone toward splitting and other types of sporadic multiplication. The location, whether singular or plural, does seem to stick to the area separating lighter and darker shades of red. This is an area that at times can be quite convoluted. No matter how the red pathway is constructed, I don’t see it as an effective barrier to the forward progress of streams of precipitable water (PW) seen occurring at that altitude. It will often pick up streams near their point of origin and do little more than to transport them for some distance before offloading. Follow-up encounters with green or blue zone perimeter winds under more constricted conditions then become definitive as to the ultimate fate of each stream.
Having mentioned PW, I had best submit today’s map, so you can examine what happens to streams as they emerge from warm subtropical waters, rise up high, and promptly enter a new world where jetstream winds are blowing. How all of this activity relates back to the air pressure differentials depicted by the blue and green zones cannot be ignored. Watching these two zones deteriorate in the future will set the stage for answering questions about the ultimate fate of each PW stream, all of which have a brief but insatiable proclivity for moving their contents—and powerful greenhouse energy effects—toward and into the polar zone.
I”m adding one more image today, showing current snow and sea ice cover, as an afterthought, mainly for the sake of archiving. The timing of snow removal will have no small impact on surface air temperatures, and thus also on the near-term durability of the blue zone, so we must keep an eye on it. Warm anomalies in northern Canada, Alaska and Siberia are possibilities that can be looked for each day, knowing they would have a hand in the timing.
Carl