A look at today’s most significant high temperature anomaly. It covers most of Siberia, and more, which means it is quite large in area. Most of it has temperature increases of about 5C compared to averages from three decades in the past, with a streak of 10C gains in the center. For further comparison, the Northern Hemisphere as a whole is plus 0.8C for this period, which is considered a strong number, and the entire planet just 0.2C, quite weak by today’s standards. Anomalies, by definition, are always special, and the biggest, like this one, are the most special, well worth discussing. The view:
Why does such a large region of exceptional warmth exist? Is there a good explanation? I think so, and I will show you why. Basically, I think it is entirely due to the influx of massive amounts of water vapor, a very powerful greenhouse gas, temporarily passing over this entire area at a high altitude in the atmosphere. The vapor has made its approach mainly in the form of two continuous streams, each of them having origins coming from warm water bodies within or close to the tropics. This snapshot plainly reveals the two large streams that have contributed the most, and possibly some others that have done so to a lesser extent:
The long streak of 10C anomaly in the top image can be directly attributed to the concentrated amount of vapor in the light-blue center portion of the larger of the two main streams in the lower image. This vapor has readings of 30kg and more per square meter, compared with averages closer to 20kg for vapors off to the sides. This comparison alone accounts for the difference in recorded anomalies from center to sides, that amounts to about 5C. I base this on the assumption of a standardized calculation that any doubling of atmospheric water vapor content will add 10C to its greenhouse energy effect imposed on the air temperature of land surfaces below when there are no offsetting factors to consider. More broadly, the normal average for atmospheric water vapor content down below on this day of the year, over the entire area of anomaly, is unfortunately not available, but could be estimated in a range of 15-10kg, naturally declining over distances from south to north. Thus, for an intact stream, doubling effectively becomes easier as its vapors move northward, which is why the strongest anomalies often show up well to the north.
The above images display numerous regions where large quantities of “precipitable water” are recorded but no corresponding warm anomalies are to be found. Precipitable water readings always include the weight of water vapor plus the weight of any of its products of condensation, when any of these are present. Such products are principally made up of clouds and drops or droplets of rainwater. Depending on the amplitude, their presence tends to have a significant cooling effect, indications of which on this day can be translated from information seen on this map:
The long trails of clearest air on this map are indicative of conditions that may have allowed streams of continuously moving water vapor to travel thousands of miles across continents with the lowest possible rates of condensing. The most favorable of these conditions is gained by making entry into the cold and dry wind system in the upper troposphere regularly occupied in part by special wind pathways known as jetstreams that vary in strength. Jetstream encounters do eventually set limits on the progress that can be made by any of the invasive vapor streams, but often not for some number of days.
Carl