North Atlantic Pressure Patterns, the NAO and the CET Record

[missouriboy]

AND SPEAKING OF RECORD NEGATIVE SUMMER NAO.  Do you suppose that it would look a little like the massive summer downturns on either side of this chart?  The left side is coming out of the Dalton Minimum.  I really need to add the last 2.5 years.  Charles Oscar II is looking a little sheepish.

[acidohm]

Jul 22, 2019 0:09:46 GMT Ratty said:

So, what does the record long negative NAO mean? Is there a consequence?

When there is higher pressure over greenland(ish) the usual zonal flow has broken. It down to the direction of rotation of air, which in an anti-cyclone is clockwise.
The southern portion of the pressure system is over north atlantic so winds here are northerly or easterly rather then westerly, the usual scenario.

That's kinda an oversimplification however, you get the gist. The normal march of depressions to Europe ceases.

Also, as air moves around the high pressure it goes up and down more. Meridionality.

High level blocking, as this is also known, is a factor of low solar.

There is nothing to suggest this scenario will exist in winter, its current long duration suggests it won't. However, this scenario in winter produces likelihood of cold for europe, much like it produces heat now.

But again, an oversimplification really, the position of pressure systems and their effects can change markedly with only a 500 mile shift, its all about where they move air from and to.

Makes for exciting weather watching.

Of course, warmists say this is due to arctic amplification and didn't predict this about now per se.
Solar types have been expecting high level blocking/meridionality, about now 🤷‍♂️

[missouriboy]

Jul 22, 2019 5:33:31 GMT acidohm said:

Jul 22, 2019 0:09:46 GMT Ratty said:

So, what does the record long negative NAO mean? Is there a consequence?

When there is higher pressure over greenland(ish) the usual zonal flow has broken. It down to the direction of rotation of air, which in an anti-cyclone is clockwise.
The southern portion of the pressure system is over north atlantic so winds here are northerly or easterly rather then westerly, the usual scenario.

That's kinda an oversimplification however, you get the gist. The normal march of depressions to Europe ceases.

Also, as air moves around the high pressure it goes up and down more. Meridionality.

High level blocking, as this is also known, is a factor of low solar.

There is nothing to suggest this scenario will exist in winter, its current long duration suggests it won't. However, this scenario in winter produces likelihood of cold for europe, much like it produces heat now.

But again, an oversimplification really, the position of pressure systems and their effects can change markedly with only a 500 mile shift, its all about where they move air from and to.

Makes for exciting weather watching.

Of course, warmists say this is due to arctic amplification and didn't predict this about now per se.
Solar types have been expecting high level blocking/meridionality, about now 🤷‍♂️

They may be claiming it now, but I remember NOAA's charts and explanations (Correct me if I'm mistaken).  As the Arctic warmed the general pressure around iceland was to become lower, which would increase the pressure gradient, thus strengthening the circumpolar vortex.  Since pressure is higher at Gibraltar than at Iceland (on average), the only way to get a lower Iceland to Gibraltar pressure gradient is to either (on avg) increase the pressure in Iceland or lower the pressure at Gibraltar.  Or both.  If you lower the pressure in Iceland, then the only way to get a lower pressure gradient is to lower the pressure at Gibraltar even more, which would imply a much weaker Hadley cell in a regime of runaway heating ... a very odd idea it seems.  Perhaps my aged brain missed something.  

[acidohm]

Jul 22, 2019 4:25:23 GMT missouriboy said:

AND SPEAKING OF RECORD NEGATIVE SUMMER NAO.  Do you suppose that it would look a little like the massive summer downturns on either side of this chart?  The left side is coming out of the Dalton Minimum.  I really need to add the last 2.5 years.  Charles Oscar II is looking a little sheepish.

Last winter abjectly failed in any northern blocking around greenland/iceland, yet roundly succeeded this summer.

Fingers point to the massive, yet very drawn out ssw that occured in jan.

[acidohm]

Now i dont fully understand this feature...

Still however notable as is the nao atm..

[nautonnier]

"Abstract

The role of convectively coupled atmospheric Kelvin waves (CCKWs) on African easterly wave (AEW) activity is explored over tropical Africa during boreal summer. Examination of the pre-Alberto AEW in 2000 highlights the observation that the convective trigger for the initiation of the AEW was generated by a strong CCKW and that the subsequent intensification of the AEW at the West African coast was associated with a second CCKW. Composite analysis shows that, generally, AEW activity increases during and after the passage of the convectively active phase of strong CCKWs. The increase in AEW activity is consistent with convective triggering at the leading edge of the convective phase of the CCKW. This convective triggering occurs in a region where the background low-level easterly vertical wind shear is increased by the CCKW. As the AEW propagates westward through the convectively active phase of the CCKW, it can develop in an environment favorable for convection. It is also shown that this phase of the CCKW is characterized by enhanced meridional vorticity gradients in the core of the African easterly jet suggesting that enhanced mixed barotropic–baroclinic growth may also be responsible for enhanced AEW activity there."

journals.ametsoc.org/doi/full/10.1175/MWR-D-12-00147.1

AEW -- hurricane forming on a 'tropical wave' travelling westward across the central Atlantic (Joe B seems to think this will be less likely this year though)

[missouriboy]

Atmospheric Pressure:

Global – 200-hPa/mb Height Anomalies – Atmospheric Pressure Anomalies at Approximately 12,000 meters (40,000 feet)
wattsupwiththat.com/atmosphere-page/

[Ratty]

Aug 8, 2019 5:39:39 GMT missouriboy said:

Atmospheric Pressure:

Global – 200-hPa/mb Height Anomalies – Atmospheric Pressure Anomalies at Approximately 12,000 meters (40,000 feet)
wattsupwiththat.com/atmosphere-page/

It appears that there is lots of old stuff there?

[missouriboy]

Time to Update NAO.  Mostly we look at NAO in winter.  People mostly ignore it in the summer.  But what does a negative NAO value in summer tell us,  Does it help explain what we are seeing right now?  Extreme longitudinal flow (loopy jets) keeping Europe cold/cool and N America hot/warm?  We have just recorded the most negative 3-month (Apr-June) NAO for the Azores to Iceland cross section since the beginning of the Azores pressure record in 1865.  The Gibraltar to Iceland cross section has been slightly higher, but consistently negative for all 3 months.  Both Gibraltar and Iceland pressure records go back to 1821, the end of the Dalton minimum.  Recent summer NAO values for solar minimums appear to be reaching those of the Dalton exit period.  What does that say about current and near future N Hemisphere summers?

[flearider]

[quote author="missouriboy" source=" What does that say about current and near future N Hemisphere summers?
[/quote]
it means we are fecked..cold cold and more cold..at least the fish stocks will recover and there might be something to eat ..
well theres always the next door neighbour

[nautonnier]

Jul 14, 2020 17:44:34 GMT flearider said:

[quote author="missouriboy" source=" What does that say about current and near future N Hemisphere summers?

it means we are fecked..cold cold and more cold..at least the fish stocks will recover and there might be something to eat ..
well theres always the next door neighbour [/quote]

if the fish stocks recover there is an argument at the moment whose fish stocks they are. Whichever side wins the argument will withhold the caught fish from the other side. So far Spanish and French trawlermen have been raking it in - they will be a little miffed if Hull and Peterhead start trawling again. And who will get the fishing rights in the Irish Sea?

[missouriboy]

If Nelson could do it, I'm sure that the Navy and the fishermen can figure out a way to keep the frogs out of the pond.  

[missouriboy]

Surface Pressures in the Azores have obliterated the summer low pressure records going back to 1865, which is when my series started.  I have added the seasonal pressure records for Bermuda and Iceland.  I collected Bermuda from Wunderground back to 1997.  I'm sure there must be Admiralty records going back into the 1800s, as I've seen crude charts.  But I cannot find a digital source.  No one seems to discuss impacts of the summer NAO, but does this pressure decline in the Azores have anything to do with the major flooding patterns we have seen spring-summer in North Africa and the southern Med, and on into the middle East?

We know that the sub-tropical high builds to the west in summer and eases back in winter.  This is clear in graph 1, which also shows there has been a clear decline in the Bermuda values over the last 24 years.  Azores summer pressures also declines gradually till about 2018, after which they have collapsed.  If Stephen Wilde's thesis is correct, declining solar output should result in lower pressures in the sub-tropical belts as Hadley cell strength declines.  Graph 3 shows that summer Gibraltar trends are not nearly as dramatic as the oceanic stations, but they do appear to be declining.  Graph 3 also shows the Funchal, which is ~350 miles south and ~500 miles east of the Azores (off Morocco), show a small rise in pressure over the period.  If a weaker Hadley cell descends further south, tha might be consistent with these observations.

Note that Azores pressure (both winter and summer) have declined dramatically in the last year (graph 3).

[glennkoks]

Missouriboy thanks for posting that. The five year summer deviation for the Azores is quite dramatic. I don't know if it part of the increase in rainfall we have seen over the last few years in North Africa or not but it certainly could be.

Part of the reason why I do not subscribe 100% to AGW is the complexity of our atmosphere, all of the factors involved and the feedbacks.

[missouriboy]

Sept 15, 2020 23:12:21 GMT glennkoks said:

Missouriboy thanks for posting that. The five year summer deviation for the Azores is quite dramatic. I don't know if it part of the increase in rainfall we have seen over the last few years in North Africa or not but it certainly could be.

Part of the reason why I do not subscribe 100% to AGW is the complexity of our atmosphere, all of the factors involved and the feedbacks.

I think that David has a chance of being, at least, partially right on this one.  North Africa was a major grainery in Roman times.  That must have required an increase in precipitation from 19th-20th century normals.  More distant periods suggest major lake systems across the region.  Be a shame to let China grab that up. It could be a much needed new frontier for African agricultural wealth if we do indeed drift back to a wetter Sahara and Saheel.