Air pressure configuration in the upper part of the troposphere, as shown on the Weather Maps at an altitude of 500hPa (about three miles), plays a vital role in the progression of surface temperature changes in the mid to upper latitudes. Configuration details in each hemisphere govern the organization of jetstream winds, which in turn maintain a powerful influence over the movement of precipitable water (PW) concentrations that exist at this same altitude. The way this movement proceeds then has a strong impact on surface air temperature due to the greenhouse energy powers of the PW. High-altitude air pressure configuration is generally represented by modest daily changes. It also passes through seasonal changes that tend to be larger, especially in the Northern Hemisphere. Today we’ll be looking at some seasonal changes.
First, I’d like to show a map of the entire global configuration, featuring a fairly straight and wide band in the tropical center of the globe. This entire belt, shaded mostly in reddish tones, is characterized by a relatively high degree of stability throughout the entire year. Jetstream winds are almost entirely missing over the belt. Temperature changes, both daily and seasonal, are minor except for a few continental areas, and PW values remain consistently high, with the same few exceptions. The processes that generate so many significant changes outside of the tropical belt simply have no real grounds available for application.
The two maps that follow are current. The shape and structure of zonal patterns in the two hemispheres are quite similar, with each of them now undergoing the middle stages of a seasonal change. In the south the pattern has hardly changed from what it has been like throughout its summer season, and is sure to remain that way through the winter. The Arctic has recently been reconfigured into a more normal and compact type of zonal pattern after being hit hard this winter by an unusual polar vortex breakdown in the stratosphere above it. The damage, in this case, was mostly on the cold side as jetstream winds were scrambled around and out of place but otherwise not weakened.
Now let’s have a look at what happened in the Arctic a year ago after solar changes had initiated their usual warmer temperatures and seasonal ice melt. This view from May 20th shows extreme fragmentation of the blue zone, a grossly distorted green zone, and even some expansion in the range of the red zone. This may have been a year of record disintegration of these zones. It certainly did lead to many extreme record high temperatures in the far north. As of now the outlook for this year is less scary, but map-readers will surely surely want to keep an eye on this daily image during the weeks ahead to see how the zones develop when compared with this one:
Carl