More map reading today. We want to know everything we can possibly learn about the formation and life cycle of atmospheric rivers (ARs). We know for sure that they originate as water vapor coming off the planetary surface in certain places where there is an abundance of water in place, with temperatures well above average (by that I mean water with surface temperatures around 25C and up). The rivers are formed as vapors collect into constantly moving flows which at first are sharply ascending, then level off and continue on horizontally at altitudes several miles above the surface. At this point the vapors have taken shape as bands of significant size but limited and well-defined width. The vapor within these bands has high concentrations, similar to the concentrations of vapor in the atmosphere above the very warmest sections of the tropical zone. Vapors that arise from evaporation of waters in the central sections of the tropical zone, which are exceedingly large in total quantity, generally do not break off as ARs. Their destiny is to collect, condense and rain out, not far from their place of birth, in a relative brief lifetime. In contrast, the vapor that does form into ARs tends to condense at lower rates after reaching a high altitude, while being transported in a direction that takes them away from the tropical zone and out over the middle latitudes of each hemisphere. Because of the relatively slow rate of condensation this vapor tends to maintain a level of concentration that is well in excess of the concentration of water vapor that is created below them from local waters of a cooler type. Ambient vapor is subject to relative humidity variations and normally remains in place in the atmosphere close to the surface of origination. It can be very dry.
Many of the ARs, before leveling off, reach altitudes that bring them into contact with wind patterns found at the altitude of jetstream winds. Doing so facilitates the possibility for a river to continue flowing many thousands of miles before its final disintegration. Along the way it will regularly lose some amount of vapor off the side as bits, and other amounts as smaller concentrations that separate from the main river and continue on. (My letter yesterday was based on the outcome of a breakaway riverlet of this type.) Most of the vapor in a any river will end up condensing and raining out at some point along the way. There is no uniform rate of timing for this activity, which means limited amounts of rainfall can occur at any distance from the beginning point of the journey. Since river beds can bend or slide sideways at any time when they are under the influence of powerful jetstream winds, rainfall and all other precipitation distributed in the higher latitudes can extend over an almost unlimited variety of surface locations.
For some time now my interest has been focused not on the precipitation activity of ARs but rather on the likelihood that their content, entirely composed of precipitable water (PW), should also express a greenhouse energy effect. The impact of the effect should be regulated in proportion to whatever amount of PW, measured by total weight, happened to be in place at any one time within a given river as it flowed along. At all points along the course of flow toward higher latitudes, assuming only a relatively slow rate of condensation, the amount of PW contained by the river should quite possibly remain greater than the total weight of all the PW—mostly just vapor—contained in the atmosphere directly below that portion of the river’s flow. The addition would always be temporary, but for as long as it existed the combination could very well be both additive and leveraging, as well as instantaneous. If so, we could expect to see large changes in overhead PW at a given location from one day to the next, and if the greenhouse effect of the overhead PW was of sufficient magnitude we could therefore also expect to see extraordinarily large warm air anomalies at the surface.
Yesterday’s letter had an example of a relatively short and small AR and the powerful anomaly it created as far north as the pole itself. Today I have a map of two large ARs that are traveling over land in the Asian part of the world, in both cases for many thousands of miles. One of these originates in Bengal Bay on the side of Southeast Asia, is fortified by more vapor that has crossed northern India, heads north across eastern China, is further fortified in north China by a river off the Pacific, continues northward and finally curls a bit westward in northern Siberia, where it abruptly stops. The other is formed from remnants of three rivers that first crossed Europe, North Africa and Arabia, merged into one large river in western Russia, proceeded toward the east, made a sharp bend to the north, and ended up over the Arctic Ocean. Notice how the color shadings in both of these long and complex rivers keep changing as contents either gain or lose weight:
Here are the anomalies they created, both of which have long stretches in the +10C area plus extraordinary areas reaching +5C. I won’t be doing any special calculations today, but if you check on the kg weights of PW on the first map, comparing those inside the rivers with those off to the sides, you should see that getting the doubles required for +10 anomalies is not likely to be a problem. The total size of area covered by the river complex on the left is possibly the largest I have ever seen:
One final chart shows the erratic nature of precipitation from these rivers, a good part of which is in the form of snow:
Carl