Climate Letter #1712

Yesterday’s letter focused on the seemingly magical relationship between highly variable air temperatures on Earth’s surface and the likewise variable configuration of air pressure zones high in the atmosphere—a region where air temperatures are largely uniform and well below freezing. I didn’t say anything about how this could happen, but if you go back to CL#1700 on June 15th there is an explanation that I still think is quite plausible. The concept of “air pressure” has two different meanings, one of which is completely dependent on effects of gravitation and the other on the physical expansion or contraction of air masses as they get warmer or cooler. When these two kinds of effects come into conflict something has to give, and gravitation-type changes may well be involved. Such changes, after all, are exceedingly commonplace on the Earth’s surface, so why not everywhere? For this to occur it seems obvious that the expansion of warm air masses near the surface must be of significant breadth and magnitude if the effects are going to be transmitted over a distance of several miles. We keep seeing appearances of exceptional conditions that prove to be capable of passing that test.

Another question may be raised about how the strength and positioning of jetstream winds is connected to these pressure changes. The Weather Maps indicate that cold temperatures at Earth’s surface tend to bring about the very strongest jetstream winds high up, which become more moderate when temperatures grow warmer, and are then virtually eliminated when the impact the warm side is dominant. I think the construction of isobar separation and gradients comes into play, but can’t say much more. What I feel quite sure about, from studying the Weather Maps, is that jetstream strength and positioning is not accidental but must be strictly limited by some version of physical laws. We can see the results through close examination of a multiplicity of overlaid Weather Map comparisons, as often described in previous letters, with a basic introduction found in CL#1681 on May 19th.

The really amazing thing, as we saw in the main example yesterday, is that strong jetstream winds are constantly appearing in geographical positions that closely correspond with the borders of strong temperature anomalies, both warm ones and cold. In both cases, just by being there, way up high and in spite of a distance gap of several miles, these winds materially help to make a given anomaly grow stronger and larger. The warm ones are able to get warmer and the cold ones colder, at least for awhile. There is a playbook involved, which I won’t discuss today but have done so many times before, making multifarious usage of overhead streams of water vapor that have their own separate set of reasons for existing in abundance in the upper atmosphere.

One more thing I do want to dig into today is the true nature of the relationship between temperature anomalies and their jetstream companions.  The strengthening of either one results in a growing of strength in the other, which is the very definition of a feedback loop.  Can we say whether one or the other is the progenitor?  I tend to believe that temperatures have the upper hand in this situation.  Temperature differentials can be created in the first place by any number of other agencies—and destroyed as well.  Once initiated and sufficiently magnified effects due to changes in air pressures are inevitable and will begin to reach out. There are other outside agencies that can eventually come into play and cause everything to be reversed. I just don’t see anything of that sort, other than temperature change, that jetstream winds are exposed to as a real influence. Water vapor streams, for example, do not appear to have any such power of their own.  What else is there to look at?

Carl