The primary driver for the amplified pattern in December was most likely solar. I have explained previously why it is inconceivable that the primary driver was the low sea ice.

The trend in arctic sea ice will remain downwards this coming decade regardless of synoptics, but I suspect the current record breaking levels (ie low for the time of year) are at least partly caused by the amplified pattern.

Originally Posted by: Gray-Wolf 

The amplified pattern has occurred many times before.  I wonder why this time it is causing record date lows for ice extent?

Originally Posted by: Gandalf The White 

I have been doing a little digging around the Internet to look at past cyles and comparing with the CET values.

The last time we were close to this current depressed level of sunspots was the beginning of the 19th century, when we had a maximum of around 50, followed by two cycles of around 100.

http://en.wikipedia.org/wiki/File:Sunspot_Numbers.png

The CET values for the first decades of the 19th century show no evidence of any significant cooling, although the winter of 1814 showed a mean of 0.4C, which is the fourth coldest in the record since 1684.

So, I'm not convinced that even with the lower values in the current cycles, that the CET will show a marked drop - but who knows in the post-modern winter....

Originally Posted by: Maunder Minimum 

Well, to be precise, extended solar minima seem to be associated with a lot of northern blocking and an amplified jet pattern. Ring any bells? Of course, in a blocked pattern, it is a matter of chance whether you end up on the cold side or the warm side of a blocking pattern. The Maunder Minimum was notable for its severe winters in western Europe, but even during that extended solar minimum, there were some extremely mild winters, when the pattern locked with NW Europe on the mild side of a block.

Climate science is now trying to catch up on this phenomenon (northern blocking during an extended solar minimum) and the indications are that stratospheric warming during an extended minimum causes less of a temperature boundary at the tropopause, leading to a much diminished and meridional jetstream.

That is my take on it. As for global consequences, it is my belief that an amplified jet pattern leads to a general cooling of the northern hemisphere, since the Pole gets warm air from the south, returning cold air by way of displacement. That warm air from the south rapidly radiates out its energy at the Poles, so with the Pole acting as a giant heat exchanger, there is bound to be general cooling, even if the Artic itself is warmer as a consequence (hence less ice build up).

All seems logical to me.

P.S. I am not referring to CET specifically, but to general hemispheric cooling as a consequence of the heat exchange mechanism I referred to above.

Originally Posted by: Maunder Minimum 

Long wave cooling to space is proportional to Temperature to the 4 th power, I don't see why moving warm air to the pole causes overall cooling. Can you quantify your argument ?

Originally Posted by: Maunder Minimum 

Moving warm air to the Pole will cool the air rapidly - as well as long wave radiation to space, the air will be rapidly cooled by the very cold ice and water over which it travels. Moving freezing Artic air south in the meantime, is bound to lead to a general cooling.

Warm air does little to warm cold seas, but cold air rapidly extracts warmth from warm seas - that is because of the relative densities of air and water. If the winter Pole is warmer, it stands to reason that somewhere else is colder - since the winter Pole does not experience any incoming solar insolation, it can only be surmised that the mixing of Polar and Temperate air masses will have the effect of cooling the Temperate regions, leading to a general cooling of the hemisphere, certainly outside the tropics.

Finally, as cold air moves south, it leads to increased snow cover and therefore increased albedo - this has to be a verifiable way in which hemispheric cooling can take place - a higher albedo means less absorption of solar radiation.

Originally Posted by: Maunder Minimum 

Well if you systematicaly increase  the area of continental snow cover then I can agree that will increase the  albedo, but is that going to happen ?More meridional flow  will results in cold and warm regions. The cold air moving south will warm over the oceans just as the warm air moving North cools. It is not obvious to me that there will be any hemispherical signal here.

Obviously summer ice and snow is much more important via the albedo effect but that is clearly decreasing in the long term

I don't see how we can get a cumulative year on year hemispherical cooling from this.

Originally Posted by: TomC 

Firstly, for cold air moving south to warm over the oceans means that warmth is being transferred from the oceans the cold air is passing over - that means cooling them.

More meridional flow will result in cold and warm regions - true, but the net effect is to more mixing of the atmosphere with pools of colder air further south than is usual (and also warmer pools further north of course - rapidly cooling in Polar regions).

A series of winters such as this one will undoubtedly reverse decreasing snow cover - expect glaciers to start growing once more - it will take a few years for that effect to become apparent.

If (and it is a big IF), current meridional conditions persist for a few more years, I expect increased albedo resulting from extended snow and ice cover on continental land masses, regardless of AGW. Extended snow cover in both extent and duration of course.

Originally Posted by: TomC 

This is quite an interesting exchange.

We have discussed the effect of an increased frequency/extent of a meridional jet elsewhere (Stephen was advocating that the effect would be to produce overall cooling).  I think we need to distinguish between the northern and southern hemispheres because my occasional reviews of the global pressure charts suggests that the absence of major land masses in the southern one means significantly less blocking and oscillation of the southern jet.

As regards glaciers, if my understanding of the processes is correct, increased snow cover will have no effect on glacier retreat for hundreds of years.   Any increased snowfall has to flow down the glacier.  If significantly colder conditions were to prevail then the rate of melt might drop below the rate of movement of the glacier and this mechanism would indeed reault in glaciers growing again.  But, just to emphasise, this is not related to snow cover but to temperature.

All this is, of course, conjecture because we don't know the relative strengths of the signals from AGW, the quieter sun and ENSO cycles.   My view is that the amount of warming in the system is such that any cooling will be temporary and regional/local and not global.

Originally Posted by: TomC 

http://img814.imageshack.us/img814/1547/piomasabssep.png

Sept. ice volume amounts. Recovery? Hmmmmm.....

Originally Posted by: Gray-Wolf 

This is quite an interesting exchange.

We have discussed the effect of an increased frequency/extent of a meridional jet elsewhere (Stephen was advocating that the effect would be to produce overall cooling).  I think we need to distinguish between the northern and southern hemispheres because my occasional reviews of the global pressure charts suggests that the absence of major land masses in the southern one means significantly less blocking and oscillation of the southern jet.

As regards glaciers, if my understanding of the processes is correct, increased snow cover will have no effect on glacier retreat for hundreds of years.   Any increased snowfall has to flow down the glacier.  If significantly colder conditions were to prevail then the rate of melt might drop below the rate of movement of the glacier and this mechanism would indeed reault in glaciers growing again.  But, just to emphasise, this is not related to snow cover but to temperature.

All this is, of course, conjecture because we don't know the relative strengths of the signals from AGW, the quieter sun and ENSO cycles.   My view is that the amount of warming in the system is such that any cooling will be temporary and regional/local and not global.

Originally Posted by: TomC 

I'm pretty certain glacier growth can take as little as 20 years, depending on the right conditions?

Originally Posted by: Solar Cycles 

Hi SC,

That wasn't the point I was making.  I am sure this is correct, as I said above.

The key is the relationship between the rate of movement of the glacier down the valley and the rate of melt.  If the rate of melt falls below the rate of movement then the glacier advances and vice versa.  That being the case, all you need in theory is one severe winter followed by a cold summer and potentially the ice would move forward.

My point was that increased snowfall would have no effect because the snow has to compact into ice and flow down the glacier - a process that takes a very long time.  At the margin, increased snowfall would sit on the glacier at lower levels but that is hardly glacial ice and so I would disregard it.

Agreed?

Originally Posted by: Solar Cycles 

It will be interesting to find out in the coming years. Problem is, we will have to wait a decade at least to see who has the more accurate picture. On the topic of glaciers, there is observational evidence that Alpine glaciers grew during the Maunder Minimum, so I would be surprised if the feedback loop took hundreds of years - I would expect to see consequences in decades instead.

Originally Posted by: Maunder Minimum 

I don't think that the position of blocks in the Northern Hemisphere is random  when blocking is favoured. The Scandinavian High for example is favoured because of the way in which wave energy interacts with the mountain range there. There are other similar regions where garvity wave mountain interactions favour blocking. So regional cooling in winter may well occur in Western Europe, indeed western parts of the continents will experience winter cooling with any reduction in the strength or frequency of westerly winds. It is still far from obvious that this will lead to hemisphere or global temperature change.

A global model could tell us a lot about this by quantifying thee processes.

Originally Posted by: Maunder Minimum 

Hi SC,

That wasn't the point I was making.  I am sure this is correct, as I said above.

The key is the relationship between the rate of movement of the glacier down the valley and the rate of melt.  If the rate of melt falls below the rate of movement then the glacier advances and vice versa.  That being the case, all you need in theory is one severe winter followed by a cold summer and potentially the ice would move forward.

My point was that increased snowfall would have no effect because the snow has to compact into ice and flow down the glacier - a process that takes a very long time.  At the margin, increased snowfall would sit on the glacier at lower levels but that is hardly glacial ice and so I would disregard it.

Agreed?

Originally Posted by: Solar Cycles 

Historically all past cooling spells have involved increased meridionality/equatorward jets.

Originally Posted by: Stephen Wilde 

Maunder Minimum said:

"and the indications are that stratospheric warming during an extended minimum causes less of a temperature boundary at the tropopause, leading to a much diminished and meridional jetstream."

A couple of interesting points there:

i) An acceptance that the stratosphere warms when the sun is less active. Of course I agree having said that for some time but established climatology says that all the atmospheric column cools when the sun is less active and warms when the sun is more active.That is why thay needed to invoke CO2 and CFCs when the stratosphere cooled whilst the sun was active.

ii) A warmer stratosphere INCREASES the temperature differential at the tropopause because the lapse rate ensures that the air rising from the surface remains just as cold as before. The increased differential strengthens the inversion hence more and stronger high pressure cells because more of the energy in the rising air column is directed back downward. Thus the polar vortex becomes weaker as less energy enters it, AO turns negative and the extra high pressure pushes the jets equatorward but the net equatorward shift is expressed by increased meridionality.

Historically all past cooling spells have involved increased meridionality/equatorward jets.

Originally Posted by: Stephen Wilde 

Interesting. And you have evidence of this I assume?

Originally Posted by: Stephen Wilde