More today about how events that occur in the upper layer of the troposphere are interconnected with air temperatures at the surface below, creating a feedback loop that can last for days. A good illustration is in effect right now in the vicinity of North America. We’ll be starting off with a shot of a particularly robust and well-formed stream of precipitable water vapor that has stayed in about the same location for a number of days already. Much of its content has originated in the Gulf of Mexico, where an intense tropical storm was rambling around for days and stirring up plenty of moisture. In brief, the illustrations will show how the vapor in this stream has produced a considerable increase in surface air temperatures, in addition to extreme precipitation, through the exercise of its greenhouse effect. The air temperature increase, in turn, has been sustained with enough power and durability to cause an impact on the upper level air pressure pattern, resulting in jetstream pathway changes. These changes have altered the pathways in a manner that assists the movement of the vapor stream by heading it in the desired direction to begin with while also opening up new and wider lanes that do not obstruct the ability of the stream to maintain its power and further its progress.
In this first image you should focus on the long tongue of streaming vapor in the center that heads far out over the Atlantic. The center of it may at first be holding up to 30kg (per square meter) of vapor in the upper atmosphere level alone, considerably more than the amount held within the lower level wind system where ocean water keeps getting colder and less able to evaporate. This stream continues by evolving into a major contributor of the vapor that ultimately ends up in the polar zone, as described in more detail in a previous letter.
Now we can look at the temperature anomaly under the stream. Of special note is the dark patch above the ocean water far from shore, which may be reaching +7-8 degrees, something that is most uncommon because of water’s high capability for quickly taking up heat from adjacent air.
Next, we will look at the 500hPa air pressure map, where we see a darkening of the red zone due to upward pressure caused by the abnormally warm air directly below. This not an unusual development. Much the same sort of thing is happening in the North Pacific, another place where vapor stream activity has been intense for many days. It’s all easily observed in this same set of images.
An important jetstream pathway is invariably created within the red zone, located on a track that runs approximately along the line that separates light red from dark. We can see the wind results in this next image, in some places tending to merge with the outer edges of winds that form on the pathway that tracks the fringe of the green zone, adding to their combined speed in the process. This image is especially interesting because you can see how the re zone pathway breaks away and loops around the shape in the air pressure pattern that was caused by the tongue of precipitable water and its warming effect. It becomes weaker in the process, making it easier for the water vapor stream to move on as before and also broaden the approach it takes, with little loss of content, on its poleward journey.
As an interesting aside, the warm air anomaly in southeastern Canada can be attributed mostly to a complete absence of snow on the ground rather than anything having to do with water vapor.
Carl