Here is something you don’t see very often, as both poles are being warmed up by close to +10C at the same time:
Meanwhile, the numbers under the map tell us the planet as a whole is undergoing a cool down period, more so in the SH than in the North. Related to the 1979-2000 baseline average, the SH has had a negative number about like this one for most of the last year or so. What is happening to make the pole location so warm today? (Actually, today’s high is still a bit below -30C.)
Things like this can happen every day on one or more spots of this continent, because a small amount of precipitable water (PW) always manages to slip past the protective jetstream barriers for a day or two. Note that the anomaly for Antarctica as a whole remains quite frigid today at -2.6C. Now let’s compare all this with warming activity in the north, where things are quite different:
This view tells us that well over half of the Arctic Ocean surface and its fragile ice cover are being warmed. We’ve watched the trend progress over the past few days, with more than one infusion of overhead PW being largely responsible. How serious is the threat that still more of these infusions could be coming? On today’s PW map I can count five good-sized stream concentrations that are either contributing or very close to doing so. Keep in mind the fact that the natural tendency of every one of these streams is to find avenues allowing them to carry their contents northward, which in this case is precisely the same as poleward. All of that “artillery,” despite any zigzagging observed along the way, behaves as if it has just one primary target in mind:
Check out the five streams in light brown and see how they release some of their content, continuing in light gray, when the brown part stops. Seemingly small bits are able to use leverage as a cause of considerable warming as they progress into this very dry region. See how the bits heading poleward from the Siberian entry point have found a narrow avenue of open passage, spreading out thereafter, and are still ending up with a great amount of warming. What stops other stream concentrations from doing the same thing, on potentially a much larger scale? The only answer I have found to this question is the presence of jetstream winds, which are positioned in ways that may sometimes aid the PW movement but usually set up barriers—as long as they stay in those positions and keep blowing as hard as ever. An illustration:
More questions: What are those winds doing there? Why are they taking these positions? How permanent are they? As stated here many times, I think they are there as a result of sharp air pressure differentials unique to the upper atmosphere, which have a pattern that serves to determine both their position and their strength. The pattern is never a secret, and it keeps changing to some extent every day. (We’ll see today’s pattern on the next image.) Nor does it have much permanence as far as the blue and green zones are concerned. These zones tend to fade away, allowing the red zone to expand, whenever high-latitude surfaces below grow warmer, becoming more like those closer to the equator that are subject to less change. Many of the jetstream winds are taken down at the same time, giving more freedom to overhead PW movement. This is a process we’ll be watching out for in the NH this summer, with regular reporting.
Carl