There is a major warm anomaly in the center of northern Africa that has been there for a number of days. We should take a close look at it and see what we can learn from the maps. These same maps will also have some other interesting things to report:
This anomaly, like the one we studied yesterday, can easily be attributed to the presence of an extraordinary amount of precipitable water (PW) in the atmosphere above. The anomaly of 8 to 9C is large enough to imply close to a double in the region’s usual amount of total PW. We have strong visualization to work with, and can quickly see that the difference between the brownish streak and nearby gray-tone areas will fit that requirement, e.g., about 16-17kg v. 7-9kg. Today we are going to dig deeper into the origin of this PW display and look for detailed information about the pathway it is taking:
This is a generally hot and dry part of the world without many local sources of evaporation. Everything points to a part of the Atlantic that sits directly to the west. Also, the shape of the imagery on the PW map suggests the formation of a concentrated stream following evaporation, with particles traveling from west to east as they move far inland. We cannot really confirm any of this without consulting the animated TPW website, where details of every such stream are depicted in a continuous way over 5-day time periods—time enough to fully cover most of their lifespans. This review, at http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php, needs to be done without any delay, and is not recordable in any way that I know of. One other thing we can do is to look at maps that can tell us whether conditions in the Atlantic are suitable for creating large amounts of evaporation and propelling it over the prescribed course. One such map, shown here, is useful because it reveals a well-placed area of clear sky not far from the equator where the water is very warm (not shown, but indicated on another map) and well-suited for an unobstructed sendoff:
Once the vapors have evaporated we need to know more about potential travel factors that can carry them for such a long distance over land. Why this particular route? Were there any travel aids available? There is a good answer, and we’ll go directly to it. This particular vapor, which may have originally headed more toward the north, is in all likelihood being quickly and completely swept up in the underbelly of a fairly swift jetstream wind that is moving straight across Africa, which we see on this map:
By studying these maps in combination it is possible to determine that the stream containing vapor—and/or any products of condensation—remains tied to this same jetstream wind over quite a long distance, probably across not just Africa but Arabia, India and beyond. Some amounts keep breaking off on sidetracks, but whatever remains continues to produce a trail of warm anomalies. One can even surmise that the mountains north of India have gotten a taste of it. What is otherwise interesting about the maps is that practically the entire parade continues with barely a trace of clouding and precipitation in the sky. How and when does the original vapor start condensing, and does it ever precipitate? It almost has to surrender in some way at some point, but any evidence is lost.
These same maps have another story to tell, one having a great deal of contrast, concerning the gigantic PW stream seen moving out of the central Atlantic in the direction of Europe. This stream has also been picked up and carried off by a jetstream wind, this one more speedy than the other. Clouding is plentiful and precipitation never stops, but the jetstream itself comes to an abrupt stop after making a sharp bend. At that point all of the remaining PW spills out, scatters, and heads off in a number of different directions. I think some of it drops down over North Africa and makes a contribution to the large anomaly we’ve been studying. The rest mostly heads northward, continuing shows of rain, while maintaining a capability to produce warm anomalies of moderate strength in a number of places. The polar zone looks like one destination.
Carl