Just a shortened letter today with map study as the theme. I have been writing a great deal about the powerful greenhouse effect of precipitable water (PW) and think it is time to do some demonstrating. Illustrations are always ready to be found, day after day. Today I will bring up two regional maps covering continental Asia, one of temperature anomalies and one of PW values, both current, where comparisons can easily be made, almost at a glance in many locations. Asia is good for this exercise because of the wide expanse of land area that stretches all the way from the polar region through the equator. It has featured a giant cold anomaly for well over a week now, sliding eastward by one or two hundred miles each day.
This map of PW readings will show contrasts that often match:
The giant cold anomaly is clearly connected to a patch of very low PW values of the same size and shape. The Himalaya mountains just to the south show even lower PW values and yet have a warm anomaly. Their average PW reading for this day would almost certainly be lower yet, because of the high altitude, and so would temperatures. A remarkable shortage of snow cover also has an important warming effect in this case.
To the north of the big cold anomaly you should be able to pick out a spike of high PW moving in from the Pacific coast that is large enough to create a corresponding warm anomaly of considerable strength. To the west there is a prominent spike of even higher PW moving eastward and creating a similar looking warm anomaly.
Much farther south you can see how the extra-high part of the anomaly in southeast China is matched by an unusually high PW reading. Moving inland, China has higher altitudes that are warming up considerably with a lesser amount of incoming PW compared with the PW input near the coast. India is sharply divided between warm and cold anomalies, both moderate. You need to look closely to see the differences in PW values, but they’re there. The southern tip of India is a more tropical lowland where the PW average would normally be high, and thus no anomaly.
Ocean waters generally have much less correspondence between PW and temperature anomalies because of the heavy influence independently produced by various movements involving ocean surface waters. Even so, well out into the Pacific to the east of Russia, you can see a pretty large example of the kind of correspondence we regularly see on land, making it quite noteworthy.
Carl