The central Atlantic ocean has cooled a little over the last month, and the cold pool that’s been there for what must be a couple of years now has become a little better organised. There are still plenty of pockets of very warm water pulsing south of Newfoundland from the east coast of America, and a noticeable warming of the North sea, probably brought about by the recent exceptional warm start to September in central Europe. The other thing that I noticed was that the warm anomalies of +2 to +3 have now gone from the Davis Straits and the Labrador sea, but the warm anomalous area to the west of Portugal have persisted. Here are two charts of sea surface temperature [SST] anomalies from the last month for comparison. I don’t know what this means for the coming autumn and winter in western Europe, possible another progressive and occasionally stormy affair like the last year.
I know it’s not quite the end of July , but I thought I would produce anomaly charts for mean sea level pressure [MSLP] so far this month, and see what influence the atmospheric circulation may have had on rainfall in parts of the south and east England. Quite a simple anomaly chart in truth, up to the 24th of the month there was a belt of lower than average pressure over the central Atlantic (-4 hPa) and higher than average pressure over Greenland (+7 hPa) and central Europe (+3 hPa). The British Isles is sandwiched between the two, with the zero anomaly running WSW-ENE across northern England with higher than average pressure to the south and lower than average to the north. The belt of anomalous low pressure in the central Atlantic ties in nicely with the lower than average sea surface temperatures [SST] in the central Atlantic. This kind of flow would have produced rather cloudy weather in the north albeit rather warm and muggy at times, the closeness of the high pressure ridge over central France would also would explain the low rainfall totals in the south. This might be a slightly better explanation than the “random distribution of showers” that Matt Taylor proffered on twitter as the reason, but I’ll leave it to you to be the final arbiter on that.
The cooler water in the central Atlantic persists, not because it’s that’s cool more because it’s surrounded by warm waters to the north, east and now west. The southwest approaches and Biscay both have positive anomalous Sea Surface Temperatures [SST] of +2°C, although curiously the SST’s in the English Channel south of the Isle of Wight are near average. If you look back to as recently as early May these anomalies did not exist. Massive areas of warmer than average SST north of Iceland and west of Svalbard persist with anomalies as high as +4°C – will that area ever see sea ice again? In comparison the Mediterranean looks quite normal. I’m just wondering what these latest SST values spell out for the coming Autumn and Winter.
There’s some kind of Kelvin-Helmholtz effect going on in the central Pacific, and I mean in the SST anomalies and not in the sky, as the last vestiges of the recent El Nino collapses to make way for a La Nina event that will start later this year perhaps. These pulses of cold and warm SST anomalies are definitely very fractal like, and I’m sure there is probably an explanation to this effect, but you won’t get it from this blog unless someone kindly posts us the answer in a comment!