How the Cold Blob In The Atlantic Is Affecting UK Weather
By Paul Homewood
As I have repeatedly emphasised, the root cause of the wet and windy weather experienced this winter in the UK has been the position and strength of the jet stream. For most of the time, it has been sat further south than we have been used to seeing it, and consequently successive depressions have hit Britain, almost as if they were on a conveyor belt.
Below is the forecast jet stream for Saturday, when the next lot of heavy rain is due to hit.
According to Intellicast:
Jet streams are fast flowing, relatively narrow air currents found in the atmosphere around 10 kilometers above the surface of the Earth. They form at the boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air to the south.
The About Education Geography website offers some more clarification:
Jet streams are also stronger in the winter because there is a large contrast between colliding Arctic and tropical air masses. In the summer, the temperature difference is less extreme between the air masses and the jet stream is weaker.
And, of course, it is this large temperature contrast that make winter storms so much more common and stronger than at other times of year.
Under global warming theory, temperature differentials between polar and tropical air should decrease, as the Arctic warms faster. And, indeed, the above website refers to “today, movement of the jet stream north has been detected indicating possible changes in climate.”. Certainly HH Lamb recognised the opposite occurring in the 1970’s, when the world was cooling down.
So why is the jet stream further south this winter? (This was also true in the wet winter of 2013/14 and summer of 2012). Part of the answer lies in sea temperatures.
As the Unisys map of SST anomalies at the top shows, there is a vast blob of much colder than usual water in the N Atlantic, extending down to around 40N. Further south, SST’s are a bit above average. And it is along this boundary of cold and warm air that the jet stream is flowing.
One of the problems with the Unisys set up is that they don’t state what baseline their anomalies are based on. Therefore it is difficult to say whether the north is unusually cold, or the south unusually warm.
However, we check out SSTs from the KNMI Explorer website. Below are the SST anomalies for 60N to 40N, and 40N to 20N:
What we find is that the southerly 40 to 20N zone is about 0.2C warmer than the average, but significantly has changed little since the late 1990s. (Graphs are based on data up to Dec 2015).
But the 60 to 40N has been running at 0.5C colder, and sometimes more, for the last year or so. It is also important to note that temperatures are back down to mid 1990 levels, and the downward trend is clear.
These are early signs that the AMO may be on the turn.
All of this is pretty basic meteorology, but how many times have we heard any of this from the Met Office? The only thing they seem interested in is playing around with models in the hope that they can blame every bit of bad weather to CO2.
I note that the Australian government is planning to defund climate science at CSIRO, on the sensible basis that “science is settled”. Perhaps it is time we did the same with the Met Office, and directed them to return to what they were set up to do. (Clue is in the name!)