Climate Letter #2058

I have learned quite a bit about atmospheric rivers (ARs) in the last few days by perusing relevant studies. You have access to the same information through links in the letters. You should be able to understand the dangers that they pose for global temperatures in the near future. These rivers are uniquely positioned, within a pair of separate wind systems, which I would denominate as “secondary,” that are superimposed above the primary wind system that spreads across the entire planet from the surface upward. The upward part is variable. Within the tropical belt it just keeps going up, all the way to the stratosphere, with no particular change of wind system. Beyond the tropical belt, in each hemisphere, secondary wind systems of a durable nature have been created, built around totally separate patterns of air pressure configuration. There is just one change of configuration, occurring in each of the two transition zones, starting at altitudes of about three to four miles above sea level in each hemisphere. The new configurations are marked by a whole new set of air pressure differentials and all new shapes for the contours that mark the paths taken by differentials of consistent strength. These pathways wander in a generally circular way around the many pressure centers that serve as generally wind-free focal points. The pathway contours are signified by unbroken isobars. All of the winds in both types of system, positioned along isobars, tend to be strongest in situations where neighboring isobars are most tightly crowded together.

When separate wind systems are set up this way, one on top of the other, a good question is naturally raised: does this arrangement make any kine of difference in how climates are created and maintained? For a scientist this means the putting together of a solid knowledge base is the first step to be taken before expecting to find answers. Scientists who are deeply interested in precipitation activity have done this, and have found some credible answers by gaining considerable knowledge about those very strange formations called atmospheric rivers. These rivers are mostly exclusive to habitation within secondary wind systems. They do not exist in any fashion within the one-system tropical belt. The rivers are entirely composed from water vapor which has the ability to make its way from the surface of evaporation to the altitude where the secondary system begins. The quantities of vapor that accomplish this feat are limited, yet substantial enough to produce significant amounts of precipitation when they eventually have condensed and fallen back to the surface. The initial uplift is of interest because it requires a steady output of evaporation from large bodies of water of the right temperature and in the right place, yielding constant flows of vapor that can go on for days without stopping. Forces must also be present that enable these flows to maintain continuous upward transport over several miles and completed in a matter of not many minutes. Upon entry into the upper-level wind system the newborn rivers must then be picked up and redirected by winds moving horizontally within that system.

This initial part of the journey can be studied by detailed analysis of everything involved, with the goal of determining how it is maintained and whether it may grow or shrink in magnitude in the years to come. There will never be a shortage of water that can evaporate, but conditions must be just right for the entire process to unfold. Conclusions from research at this time are that conditions appear to be right with respect to growth in magnitude at possibly increasing rates, which means untold quantities of additional vapor could be inhabiting both systems in the future and following whatever rules of behavior are imposed therein. This makes good sense for those who do rainfall event forecasting. I just don’t see any comparable effort on the part of other climate scientists, who might wish to gain knowledge related to the effects these streams may have on the development of future temperature changes. The people who do AR research have laid out new information that could have powerful effects of this type, some of which are perhaps already being realized, yet not properly understood.

The map below reveals current one-day surface temperature anomalies all over the globe. The most outstanding bit of information is in the numbers at the bottom—where we learn that the Northern Hemisphere is 1.1C warmer today than it was during a baseline period averaging 30 in age. That’s a pretty high number, almost twice the global average and almost four times as great as the tropical zone by itself. Bear in mind the fact that half of the tropical zone happens to lie within the NH, helping to hold its average down. I would guess that the anomaly number for land and surface ice only, without either open ocean surfaces or the tropics, would run no less than +1.5C and probably quite a bit higher, although nowhere near the Arctic Circle alone at +2.8C. None of these regularly selected anomalies is unusual these days, and the same can be said for anomalies throughout the SH. Why are things so warm in the north, so much less so in the tropics, and literally a bit less than the average of 30 years ago in the SH below the tropical belt? I believe all of the answers can be found by examining things that are going on in the upper wind system of each hemisphere—and not going on in the case of the tropical belt—involving the formation and subsequent behavior of atmospheric rivers. These rivers must be doing things in the north, and north only, that they were not doing thirty years ago—more vapor content and more poleward movement for a good part of this content. Together, these two changes generate the power needed for us to see exactly what we are seeing with respect to temperature anomalies. All this has happened in no more than 30 years. What is in store for us in the next 30?

Carl