Today we’ll start with an image of high-altitude air pressure configuration, featuring an odd break in the green zone of the NH that stands out like a sore thumb. It’s not an accident. It’s there because the region directly below has stayed unusually warm for almost two weeks. I learned this by scrolling through old Climate Letters back to September 22, seeing quite a few images that were that were all consistently warm in practically the same place. Warm surface air expands, steadily pushing the air above it to higher levels, which will effectively raise the altitude of 500 hPa readings in that location if the warming continues. That is exactly what the sore thumb represents at this moment in time. Once established a feature like this automatically creates a mechanism that supports its own perpetuation, which we will look for next.
What we are looking for is irregularity in the major jetstream pathway that is always found tracking the fringe of the green zone. It should leave some kind of a wide gap and considerable weakness in wind strength where the bulge begins, and that is exactly what we see on the map for today. There is no other gap or breakdown anything like it in either hemisphere.
Anyone who studies the behavior of streams of water vapor that have entered the airspace at this altitude knows that a gap like this is an open invitation for one or more streams to cut through and find passage into higher latitudes—as nature always urges them to do. We can see on the next map that this has actually happened, with a stream in place and and able to take full advantage of the situation. The primary vapor stream can be identified as one that originated from a specific location off the west coast of Africa only three days ago. (I have gained a good view of this information from the animated website for Total Precipitable Water.) Traces of the stream’s past course and ultimate depth of penetration into the polar region are plainly visible on this map of its current position:
Water vapor’s powerful greenhouse effect becomes exaggerated when high concentrations of these molecules are added on to the normal concentrations held by air closer to the surface. The result for any one day when a mass of concentrated vapor happens to be passing over as part of a separate wind system will be a warm temperature anomaly. The next image has the result for today, using a map with a different perspective to better assess the breadth of coverage. Note that Greenland’s exceptionally dry air was the most strongly affected. I think the Atlantic source of this stream has been overcome by heavy cloud formation during the last couple of days, which is why we are not seeing any warming effects over land near Africa’s west coast that is close to where the source was. If this source of vapor is not soon replaced, which now seems likely, the “sore thumb” in the first map will disappear, the jetstream will tighten up again, and, for a while anyway, future vapor streams will no longer have such easy access to either the continent or the polar region through a portal in this part of the world.
Carl