[Wiseacre]

There is currently much debate on this subject, but it is ridiculous to draw conclusions from a small number of years. There has definitely been a shift in the synoptics in the northern temperate region in the last 5 years to more meridionality (blocking) and this has resulted in colder winters and summers for the UK and parts of W Europe. There does appear to be an element of story shifting and backtracking on the claims made a few years ago that we would never see snow again in the UK.

The reality is that there will be winners and losers in any change of world climate however it is caused. Trying to make computer models fit the synoptics is just as crafty as trying to make the temperature record fit the curve!

[ldavidcooke]

Hey Wiseacre,

For definitive or near precise values, concur. Its the problem of figuring out the functions first. So far most models are large scale top/down. I figure we need a bit more empirical work first. The problem it costs tax money to perform a field campaign. I can just imagine being in one of the leading Climate Science teams knowing you're, "dammed if you do and dammed* if you don't"... (*Note: Misspelling of explictive on purpose.)

(Done right we need some form of Argo buoy for the atmosphere. Kind of like a helium balloon that captures/dumps condensed water vapor to vary altitude. The problem is finding the right materials and not impacting air traffic.)

[ChaserUK]

Is this for another thread but what I have noted is lack of sunspots. We are supposed to be at solar max - no where to be seen sunspot-wise (forget coronal holes causing geomagentic activity). This follows a historic quiet period of the sun since records began. Are we not now experiencing a cumulative effect of what is being discussed here and the sunspot (lack thereof) factor.

[Anabolic North]

Melting Arctic does not cause UK snow.

Nonsense...you should all be ashamed of yourselves. and who says the Arctic is melting anyway?

And what about the record levels of Antarctic ice?

[ldavidcooke]

Hey Martin,

Now you know a picture is....

[Wiseacre]

You should not be so confident in your view, Martin. Whether we like it or not, there has been a decline in the size of the Artic sea ice area and the volume of ice, both in the summer and the winter. With such a shift in the thermodynamic balance of the atmosphere/sea system there is very likely to be an effect or two and not necessarily restricted to the Arctic area. I agree that it is not possible to directly connect ice loss with cold winters in the UK, but the likely change in the temperature contrast between the tropics and the poles as a result of the ice reduction is likely to impact the position of the polar front and hence the distribution of the pressure systems in the Northern Hemisphere. I am not ashamed of conceding that.

[John Mason]

It's certainly an interesting topic. The focus of the current research is the behaviour of the Polar jet, which, like a river entering the lowlands from the mountains, has slowed and developed bigger meanders. Given that a key driver of this jet is the temperature gradient between the Arctic and the temperate zone south of the jet i.e. the Polar Cell and the Ferrel Cell, and given that the Arctic has warmed over twice as much as anywhere else on the planet, it follows that the driving force has eased off as that temperature gradient has decreased in magnitude. The enhanced meandering then permits Arctic air to have an easier time of it in penetrating southwards; plus, the slower eastward progression of the waves leads to more prolonged periods of one weather-type or another. Recently this pattern has kept us stuck on the Polar side of the jet for a prolonged period: however, that is simply where we are now and the opposite could happen too, where we become trapped in the middle of an upper ridge on the warm side, bringing prolonged warm dry weather - as has indeed occurred across large parts of the USA, where severe drought has resulted.

All in all this is something to watch for the simple reason that it brings major problems to agriculture, which in turn could lead to substantial hikes in food prices on top of those already experienced, which are more a reflection of the massive increase in global oil prices in recent years. My advice is start growing your own, if you have not already, and get good at it!

[John Mason]

This new paper at PNAS is worth a look too:

http://www.pnas.org/...000110.full.pdf

[ldavidcooke]

Hey John,

The issue is not that the speed has dropped; but, that meanders have developed. In addition, though the surface level Summer temperatures have risen, the Winter time and Upper Level air has not warmed. At least the warming that has occurred has in essence radiated out into space and is greatly diminished in the Polar cell return flow. That I think is the main issue, the thermal increase at the surface has increased the amount of air parcels in the Arctic which ends up expanding the Polar Cell pushing the UL winds into the Hadley Cell region. The interaction at the edges is what is giving rise to both the "wild weather" and the meanders.

The Ferrel cell has always been a, " if come, maybe " kind of feature. Similar to the " feeding jet " of a blackhole, it has the character of existing mainly where there was a clean Hadley/Polar convergence, where the in essence "outer layer scud" mixed and rotated above the convergence acting as a form of UL bridge. The more erratic the convergence the greater the outer layers were shed and in essence fed a secondary circulation cell. At the current erratic flow the Ferrel cell really is not an observable feature as the strong counter rotating features are driven by the thermal UL differences between the higher latitudes and the surface level in the lower latitudes. In essence, in the past the circulation cells were more like a closed system, very little energy was exchanged. (Any exchange was purely the energy transferred at the surface or ground level by ocean surface currents.).

Once the convection energy changed the Ferrel cell broke down, and the interaction at the Polar/Hadley convergence increased. It is the energy transferred at the convergence zone, further pushed by the added convection in the former polar region caused by higher sea surface temperatures that is responsible for most of what we are seeing. At the same time that the upper level of the Polar cell has pushed South the surface level of the Hadley cell has pushed North. In essence, no more closed cell convergence; but, constant convection cells both rising and the return flow.

[John Mason]

No it's both speed and meanders if Francis & Vavrus are correct. A lot of their recent work has involved assessing both windspeeds and meander latitude.

[ldavidcooke]

Hey John,

That's the point, they aren't right. The wind speeds within the Polar Jet Stream have not diminished. The only real effect is that the ground speed has changed. Increase the ground to be covered under a wind speed that has not changed and yes you could interpret that as a reduction in ground speed; but, that is disengenerous at best and fraud as a possibility. This is the type of science that infuriates the reasonable against the cause of the "warmists" pov. A little tweek here a contentious interpretation there and it is clear that the conspiracy against honest examination of the facts feeds my personal anger over conclusions which misrepresent the facts and fuels my personal disgust. That both sides use similar misrepresentation does not absolve either party, they simply expand the disdain of the public at large.

[John Mason]

So all their years of study of the subject count for nowt because you say so? Forgive me, but that's really not very objective!

[ldavidcooke]

Hey John,

Its simple really, if there was a reduction in the UL wind speed I could accept their "years of expertise". No they were not measuring wind speed ; but, the progress of an air parcel as it advance on the circumference of the Earth, please... Read the paper and the examination if you question my interpretation. If you are that concerned that they are being honest brokers have the folks at Skeptical Science have them submit a guest article. I will be surprised one if they will open their examination methods beyond the public satellite monitoring of UL cloud features and their advance over the ground. This is not a valid measure of a body of air, it is a measure of the effects of its passing. Its like trying to measure the speed of a passing lorry by the displacement or wind speed of its passing...

I find that disengenerous at best! I really cannot express my full displeasure in a public forum, which is probably a good thing...

Put another way, if the exhaust of a car exits the muffler at a rate of 100km/hr how fast is the car moving...?

[John Mason]

Here's the graphic in question:


This graphic depicts how the drop in high-altitude winds in autumn over the past 30 years has closely tracked the decline in Arctic sea ice (dashed line). The rapid warming of the Arctic has reduced the temperature difference between the Far North and temperate regions, slowing down the jet stream and leading to more persistent, or “stuck,” weather patterns. (Jennifer Francis, based on data from the National Center for Environmental Prediction, National Center for Atmospheric Research, and National Snow and Ice Data Center)

[ldavidcooke]

Hey John,

That is not the Jet Stream, try the graph for 250mb.

[John Mason]

One might think so Dave, but the authors state:

Fields of 500 hPa heights are selected for this analysis because they are constrained by observations from numerous radiosondes and satellite retrievals, they are relatively free from surface effects, and they capture upper-level wave patterns.

I find this holds time and again when figuring out shear profiles in thunderstorm forecasting.

[ldavidcooke]

Hey John,

So is standing on the side of the road going to be a measure of the passing lorry. Move further away from the road and the wind speed will drop. Increase the average atmospheric turnover from a 10-12km height to a 14-16km height and what do you think happens to the measured wind speed. I'm so sorry; but, 500mb is not the jet stream. Matter of fact on the SRRS server for nesdis I have watch over the last 10 years as the 300mb measures have narrowed and the 250mb measures have broadened. Certainly there used to be a seasonality, Winters were broader at 300mb and narrower at 250mb. Then we started seeing around 2006 that both seemed about he same breadth. Now we begin to see the 300mb narrow and the 250mb broaden year round.

The point is, BINGO, they were not measuring the Jet Stream rate, period!

[John Mason]

From the abstract:

Daily fields of 500 hPa heights from the National Centers for Environmental Pre-diction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of pole-ward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude.

What they are saying is that 500 hPa observations can characterise how Rossby Waves are behaving. I see no problem with this. For example, compare these three charts:







You can see that the 200 hPa and 300hPa windfields, including strengths and positions of jetstreams, are well reflected by the 500hPa pattern.

[ldavidcooke]

Hey John,

What do you think a Rossby wave is?

I'll share my thought, it is the point of interaction between the Polar and the Hadley Cell. If the energy balance favors convection it's a cyclonic wave if the energy favors subduction its an anti-cyclonic wave. If there is a "greater" thermal imbalance by surface latitude, the Polar cross zonal flow increases, if the circulations are closed as when the polar air mass reserves are balanced both gravitationally and in vapor pressure, then the cross zonal flow is minimal or reduced. Just the opposite of current theorms, it is in the NH Winter that the Polar air masses move over the NA continent, not Summer.

However, the point is the Jet Stream has not slowed, its gotten longer. I agree that Rossby wave progression between 20-60N have slowed. However, that does not reflect on the speed of the Jet Stream though. Instead of suggesting a weaker Jet Stream it makes more sense to suggest a stronger N/S meridional flow, driven by circulation change caused by thermal/climatic zone overlapping.

The global atmospheric circulation is the driver of the meanders, the blocking and cutoff conditions, which are symptoms of gravitational changes related to thermal changes in the thermodynamic balance at the global boundary layer where advection and convection merge. In a balanced system most energy would be advected away from a point of excess towards a point of stasis. If the energy at the point of excess exceeds the ability to be advected away we get increased convection, the combination of which changes atmospheric circulation.