Climate Letter #1921

Today’s letter will be devoted to commentary related to the 5-day animation website of total precipitable water (PW), produced by a group of scientists and engineers based at the University of Wisconsin – Madison.  I find it invaluable as a tool of understanding for how this complex body of material affects our everyday weather conditions.  The website is updated daily, available at http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php.  A great deal of effort and expense underlies the creation and maintenance of this imagery, the current version of which has only been published since 2016.  Since NOAA is heavily involved I believe the primary purpose is intended for usage by the meteorological community, as an assist for improving the accuracy of precipitation indicators that are such an essential part of daily weather forecasting.  PW is rarely if ever referred to in any kind of science literature as a primary source of causation behind globe-wide temperature changes.  In my mind this is a deeply significant oversight that needs to be corrected, with climate scientists rather than meteorological scientists doing the heavy lifting. Awareness of how and where these trails of PW concentration originate and how to follow them to the end of their short lifetimes can only be of great help in observing exactly what their total effect is along every step of the way.

By “total effect” I am talking about temperature effects, not just precipitation.  The animation site has nothing of its own to say about a temperature connection.  For that one must switch over to Today’s Weather Maps at https://climatereanalyzer.org/wx/DailySummary/#t2 and check out the section with PW maps.  This can be confusing in one respect, because the maps are designed to tell you where all of the PW in the atmosphere is positioned on that day, regardless of how it got there or how long it has been there. What appears to be a long, integrated trail created by a concentration that is nearing the end of its run is actually a composite of snapshots of trails that began on following days from about the same location. One thing we learn from 5-day animation is that the sources of PW stream concentration on the borders of the tropical belt shift a little every day, of may even come to a halt. The same things are true of the courses that are followed thereafter. The weather maps cannot restore all of that information, but they do guide us to good information about temperature effects that are happening everywhere, currently, from all concentrations in all stages of trail variation.

Moving on to a different subject, the animation imagery always shows us a clear division between PW activity within the tropical belt when compared with the higher latitudes. Within the belt there is no outstanding sense of differences in direction of movement. On the outside, one direction dominates, west to east, plus a strong tendency for material to move outward, or toward the nearer pole. This needs some explanation. We know that “total” PW represents a measure of all the PW in the atmosphere above a given location, at every altitude. We also know that the most familiar kind of PW, composed mainly of water vapor at ground level, does not move around in any such way, with or without wind carriage. Often it does not show much change or move anywhere at all for many days. That means something other than ground-level water vapor must be responsible for a substantial portion of the total, because of the constant motion, constant change, and singular directional effects that total PW has in the higher latitudes. The only possible explanation calls attention to the level of the atmosphere that holds jetstream winds and its peculiar form of activity. There must be substantial amounts of PW up in that same part of the atmosphere, quite possibly exceeding amounts closer to the surface in a substantial way much of the time. We can always see considerable differences in the engineered measurements of total PW concentrations every day, accurately representing full totals and constantly varying from any one place to another. More common measurements of surface level water vapor show differences as well, but not of the same magnitude, and bear patterns quite unlike the patterns of variation found in the engineered measurements. One cannot avoid thinking about the suggested implications, that something special is going on with PW in the upper atmosphere on a very large scale, and it could be having an effect on the temperature variations at the surface that also occur on a very large scale. The animation of total PW shows us the truly dynamic nature of how those variations come about.

Carl