Yesterday we looked at the principal physical mechanism that causes the pattern of high altitude air pressure to be configured in the manner observed, keyed to differences in surface air temperatures. Today I wanted to write about the effect that any existing configuration has on surface air temperatures, in the form of feedbacks. However, an unusual development has appeared on the Weather Maps which needs to be treated first, having the potential to be invoked afterwards as a prime example of how the wanted feedback works. To set the stage, I first need to review and reemphasize some general observations pertaining to the strength and location of jetstream winds, which strictly follow certain pathways formed by air pressure gradients and behave in a manner marked by pulses of intermittent strength. The strongest winds occur when the gradients are sharpest. At this time the gradients in the south polar region are much sharper than those in the north and thus contain much stronger jets. You can see how this plays out today by looking at this next map of jetstream wind bursts and referring back to the north and south polar region air pressure maps in yesterday’s letter for comparison. Now take note of the strength of the jet wind crossing the center of South America, effectively cutting the continent in two, which is a key part of this discussion:
Referring to the following map, this jet basically tracks along a regular pathway set within the red zone of air pressure, and then gains added strength when its pathway closely approaches a separate regular pathway on the fringe of the green zone. The latter is also accountable for creating the strong jet that is observed above as it crosses the southern tip of the continent before the pathway makes a sharp bend as part of a northward jog that soon peaks and heads back south again. The jet will temporarily lose speed while making the jog, then merges with the jet on the other pathway. This map clearly describes all of the movement of these two pathways. There is a third jet involved here that is too weak to be seen but still has some effect on the outcome. It follows an irregular pathway set up by the red-zone fragment on this map that can be observed off the coast to the west.
The combined effect of these three jets has been to completely seal off the airway over much of the southern half of the continent, preventing the potential entry of a number of streams of high-altitude water vapor flowing into the region from several directions. In particular, notice how the heavily loaded stream heading south from the rainforest in the next map is completely brushed aside by the most powerful jet. The overall result is a patch of atmosphere having greatly reduced water vapor similar to that of icy Antarctica:
The extraordinary absence of the most powerful greenhouse gas should have a significant cooling impact on surface air temperatures and that is exactly what we see on this next map, where some spots exceed minus-10C. This extreme anomaly is the result of developments going on around four or five miles high in the atmosphere, things that cannot be seen by human eyes but are open to instruments.
This anomaly was created on short notice by an accidental arrangement of several jetstream winds. It has not yet had time enough to establish an ordinary cold type of imprint on the high-altitude air pressure configuration as a feedback. This can still occur, probably by means of an expansion of the nearby green zone, and I will be looking for that on tomorrow’s map. Moreover, any such expansion of the green zone should effectively shift the jetstream pathway on its fringe outward to the west, where its jets might then be able to single-handedly hold off incoming vapor streams and thus prolong the life of the cold anomaly as a feedback.
Carl