Yesterday we looked at the stark differences in 30-year temperature anomalies between the NH and SH, and drew a few possible conclusions respecting causation. It’s a really fascinating subject because of all the future implications. Today I will add some more visual material that can be further reviewed as the seasons switch over the next six months. We’ll start with a picture of the current high-altitude air pressure configuration in the north, which you can compare with the one in yesterday’s letter. Yes, the three little blue zones will consolidate into one, and create a renewed jetstream wind pathway of reasonable strength, but how will it compare with the one we now see in the south? How much the latter weakens in the coming summer will be just as interesting.
Now we’ll turn to one of the most critical differences between the two hemispheres, the sea surface temperature anomalies that have developed over the past thirty years. I’d say that, overall, they are more extreme than the air temperature anomalies, signifying extreme differences in causation. Anyway, whatever is causing Antarctica’s ice shelves to be melting on their undersides is not leaving leaving much of a signature on the surface water, but the same cannot be said for the outflow of ice-cold meltwater that is most likely the result.
Next, a detailed look at the pattern of air temperature anomalies in the south. The most extreme cold ones, which reach close to -20C in spots, do not appear over the elevated and extremely cold continental land mass, nor anywhere over open water. Instead, while hugging the shoreline, this very cold air is largely perched on top of sea ice, thus right at sea level. You can refer back to the map just above to see how snugly the borders fit:
The next map shows that actual below-freezing temperatures for the whole region extend a little way farther out than sea ice, but not much. The sea water soon reaches +3 to 5C, as does the air above it. The question is, why does so much of this surface air drop all the way down to -30C by the time it reaches the shoreline? The anomaly (up to -20C) is telling us that thirty years ago, on an average day at this time of year, air temperatures of similar location were dropping to only about -10C. I think the much bigger drop we see in today’s chart is fairly regular, not just a one-day extreme. Why so?
The best answer I can come up with is found on the Precipitable Water (PW) map. Concentrated streams are getting close, but just cannot do much penetrating of the jetstream wind wall that is set up around the blue zone, as detailed in yesterday’s letter. So instead of getting PW readings of 10kg and more, which the streams are carrying, all we see on the “inside” parts of the sea ice are readings that range from below-1kg to +1 or a little bit more—leaving plenty of room for declines that can cause the big anomalies. I suspect that the blue zone is larger now than it was thirty years ago and that the jetstream wall around it was probably not as strong then as it is today, but have no hard data as evidence. I wonder if the needed data is filed away in some place where it could be accessed?
Carl