What happens when the prevailing pattern of jetstream winds in one of the hemispheres reveals signs of weakened strength and poor positioning? Today the weather maps have images that give us the answer. We can even compare one hemisphere where this is happening to another where the jets are strong and solidly positioned, as we see here:
When jets are at full strength and well-organized they are most effective in blocking the freedom of movement of precipitable water (PW) concentrations that have gained access to the upper troposphere. Those concentrations form from surface waters existing at latitudes of around 20-30 degrees north or south, quickly rise upward several miles in altitude, where jet winds are to be found, and from there have a natural tendency to migrate poleward—if the winds cooperate. (You can watch how they take these steps on any day at this animated website: http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php.) Jet winds are the only thing that stands in the way of their favored migration, and for the PW this part of the journey is like finding one’s way through a maze. Here’s the result for today:
The massive amount of PW angling straight across Europe, from the Caribbean Sea area to the northern coast of Siberia does not seem to be having any problems. Where do you see any real barriers? Another mass has found an opening in the center of North America, allowing it to move ahead over a shorter distance before being blocked. Both of these active streams of high PW concentration are constantly producing greenhouse energy effects, which are big enough to show up at the surface below like this on the regular temperature map:
We can learn from the anomaly map how great the departure from normal becomes. One part of Siberia is actually seeing temperatures about 15C above its past average. With the entire stream looking as if it were widely established over many thousands of miles, we can wonder about how long this situation will continue, and what does it mean for the deep layers of permafrost in that region?
I want to show an extra image today, taking us back to the sources of PW streams that are able to rise to such a high altitude. Suitable locations for these sources are restricted by a short list of requirements, which are only met in certain spots along the outer perimeters of the tropical belt. Water temperatures need to be not less than about 24C, with plenty of it on hand. Air currents that do the lifting of the vapor must be unobstructed, continuous, and outwardly directed, merging easily into the outer parts of either upper-level wind system. Rain forest transpiration on a large enough scale may also qualify. Use this map for a separate view of the locations that you already see working on other maps.
Carl