A theme I keep coming back to, rather cautiously, concerns the role of high-altitude air pressure configuration as a factor that affects the progress of climate change. It is a difficult thing to get my head around, and perhaps you have the same trouble. Each time I come back to it the picture gets a little clearer. I now feel more confident than before that this factor does not simply affect the way weather patterns develop over an extended number of days; I think it also has serious and not well-recognized implications for future climate change as well. I tried to condense this idea into a few short paragraphss in yesterday’s letter. Now I need to work on improving the presentation in greater depth. Today will be nothing more than a review of several basic elements.
The configuration image we see on the map represents a natural phenomenon that is certainly real, while defying every attempt at a simple explanation. Just think of it as a near-bottom layer of a pattern of air pressure differentials that will remain about the same in the troposphere above, but differs considerably from the pattern in the air below. The changeover between the two patterns is complete by around the 3-mile point in altitude. Just below that level there must exist a zone of some depth where things get sorted out in a way that finally determines the shape of the upper-layer outcome, which keeps changing at a slow pace. I think the extent of those changes is heavily dependent on upward air pressure inputs due to the expansion and contraction of pressures generated by air temperature changes at the surface. If you look closely at these next two maps every day you will find broad outlines in their respective imagery shapes and sizes that consistently support such a conclusion—in each hemisphere, day after day.
The configuration that we end up with on the map, because of these upward pressure adjustments, must be making a sensitive response to surface temperatures. I see no alternative. Does this mean anything, from a practical standpoint? Yes indeed. The shape of this revised upper level pattern of pressure differentials will become a fundamental determinant of the way its incumbent winds will be blowing. This conclusion simply follows the same principles that govern the organization of wind patterns at the surface. The only difference is that now we have a whole new pattern of air pressure differentials in place, actively setting up the way the new organization will function. Same principles, but the new organization will bear a few of its own features because external conditions have changed. Winds will appear that may have jetstream velocities, although not constant. They will stick to certain prescribed pathways, which are determined by air pressure differentials of a certain type, not quite the same as the ones we see at the surface. There are usually, but not always, spaces between these pathways that remain much less windy, and the same can be said about an extended amount of space that lies in the center of a quite large region that is basically surrounded by jetstream pathways. This next map provides a good look at how each of these things plays out in creating the outcome for today. Every new day should have an outcome beholden to the same basic principles.
The interaction between jetstream winds and streams of precipitable water (PW) that have gained entry into that level of the troposphere is a story I have related many times, and see no need to repeat today. I do want to show a map of the final result for today, as revealed in terms of the relative amount of PW that was able to navigate an entry into the large and less windy space surrounded by jetstream pathways, as described above. This is something of fundamental importance that should be checked out every day when looking as the other three maps.
Almost everything in dark gray, having PW values of 5kg or less, fits inside the borders of that central and mostly wind-free space. One contrary feature within the space is noteworthy, visible as a small and circular jetstream wind pattern near the top. This one marks a pathway not often seen, on the perimeter of a very deep blue section within the blue zone of air pressure—associated with extremely cold surface air. The PW value for the area inside this interior jetstream pathway is less than 1kg, which in and of itself helps to keep the surface below from getting any warmer. This correlation is a definitive example of a fully operative feedback loop.
Carl