Climate Letter #1781

Some thoughts about streams of precipitable water in the upper atmosphere. I think they are of critical importance to climate science, but that view is not in accord with the way climate science is being taught in the universities. The streams are real. There is no question about that. Meteorologists know they are real, where they come from and how they expire. They know the streams are made of water molecules that have mostly evaporated from tropical ocean surfaces, been transported over distances that extend up to thousands of miles, even as far as the poles, and at some point dropped as precipitation. How else does one explain where the precipitation in deep continental interiors comes from? Meteorologists have created some wonderful maps and charts for us to look at and follow the courses of these streams, even animated views. Yet meteorologists have little to say about making a direct connection between these streams and surface air temperatures, perhaps because they have found other ways to predict air temperatures with considerable accuracy.

A more thorough study of these streams is badly needed, not just by meteorologists but by climate scientists as well.  What these streams are mostly made of is not something immediately precipitable, like rain, snow or hail, nor even an intermediate substance like the stuff of clouds.  They are mostly made of pure, uncondensed water vapor that is originally added to updraft winds in relatively high concentrations that are adaptive to stream formation upon leveling off at high altitudes.  Condensation may soon begin, but the remaining vapor in these streams will always have a powerful greenhouse effect, no less effective per unit of volume than that of vapor closer to the surface.  At whatever point a parcel of stream is passing over, the greenhouse effect of the vapor it carries is naturally added to that of the vapor below, along with all the other greenhouse energy inputs in the atmosphere.  A heavy parcel will have a strong effect, everything less according to scale, down to those infrequent days when no stream at all passes over and there is no effect to be had. 

How important is this added effect? I can see no better way of gauging than through the study of temperature anomalies at the surface. We know from the maps and charts when and where a stream of vapor is passing over, and we can even estimate—not perfectly but within reasonable bounds—the amount of vapor it holds. We also know if there is a concurrent warm or cold temperature anomaly at the surface below, as measured almost to perfection. We can easily put these measurements together, along with everything else we know about temperature anomalies, and look for consistent patterns. Trained personnel should have no trouble delivering reasonable answers on a large scale, and those answers could be useful.

Purely as a lone hobbyist, one who puts his hand to this kind of task day after day by studying the maps and charts, what I continue to come up with is not just a close association but some pretty big numbers. At one extreme, an almost complete absence of daily overhead vapor, I keep seeing cold anomalies of around -10C in mid-latitudes and double that within either of the polar circles. Relatively heavy-looking streams, when present, are typically associated with exactly the opposite effect, or even a bit greater. Streams of an in-between type usually result in little or no anomaly either way. As for the tropical belt, where precipitable water content is generally high to begin with, streaming activity is blunted and not amenable to the making of practical connections.

I think that nearly every location on the surface of the planet’s mid to high latitudes will have its temperature affected every day, one way or another, by the passing over of one or more parcels of streaming vapor in volumes that are highly irregular. From this one particular source of anomaly, temperatures on some days can be 10C or more above normal or the same below. The potential for cold extremes implies that on an average day, everywhere, at least 10C of the actual temperature we experience is derived from the presence of this one special source of greenhouse energy. Thus, it follows that if no streams at all were being put up there for some reason our planet would probably be at least that much colder! On the other hand, consideration should always be given to the possibility of changes in the volume or activity of these streams that could add to warm anomalies. This probably will not happen until the activity itself, and its observable effects, as described above, is more widely recognized.

Carl