Sea Surface Temperature And Sea Ice Trends

[summer blizzard]

After the stormy regime between the 5th and 15th September, we should see a unsettled but more settled regime afterward unless the AO is positive in which case a short heatwave may be possible between the 15th and 20th September.

In summary, this Septembers weather will be dependant upon the AO.

[summer blizzard]

I thought that it would be good to compare the current setup to 2005. As you can see, the situation in the Pacific is a lot more amplified although there is a bigger thermal gradiant just to the west of the USA, so we may see major storm development here, charecteristic of a negative PNA pattern, in the Atlantic, the situation is broadly similar aside from more average sea surface temperature anomolies in the western Atlantic, increasing the chances of a southerly tracking Jet Stream, once again, this should enhance the thermal gradiant however sea surface temperature anomolies are condicive to a neutral to negative NAO, not positive.

I have illustrated a chart to show the probable Jet Stream pattern, the circled areas are areas of mean storm development due to the phasing of Jet Streams.

Edited August 29, 2006 by summer blizzard

[Stratos Ferric]

I believe this explains the recent northerly type weather, because the warm west/cold east creates a north to south thermal gradiant, as the current sea surface temperature anomolies go, a negative NAO is favoured in early September, i we can get stronger extra-tropical banding, then we could see quite a strong negative NAO.

I think you mean an E-W gradient don't you SBz?

The effect of a warm ocean surface would be to displace the PF polewards, and all other things being equal to push the jet core into a loop above (poleward) and around the warm column. Beyond this simple statement matters at the surface become slightly complicated. The jet moving polewards will tend to accelerate, causing uplift at the surface, thus favouring depression formation (in this case off the E seabord of the US). The equatorward swing would ordinarily see convergence aloft, descending air and divergence (HP) at the surface. This would favour a HP area somewhere W/SW of the UK. That, however, is not what we're seeing at present and should signal that the system is, in fact, more complicated than this - which it is. Downstream drivers cannot be ignored, nor can upstream modifiers, and the Pacific is at least as important in driving the motion of the PFJ as is the Atlantic. In addition there are short-term feedbacks. A deep surface LP introduces a lot of warm air poleward at the surface, effectively pre-empting an easing of the thermal gradient, and so a slowing of the jet, convergence aloft, and so filling at the surface; hence some large systems with dynamic motion during genesis can slow significantly as they initially deepen. Equally, behind the surface LP, colder polar air will flood in, strengthening the gradient again, and potentially accelerating the jet, so causing divergence aloft and uplift from the surface, and moving surface systems forwards again. Finally, a warm ocean surface itself tends to favour vorticity. Given that the jet behaves to protect absolute vorticity it will then tend to move either equatorwards or polewards to effect a vorticity reduction or gain (relative to the spin of the earth and the coriolis effect).

As we head into winter I'd suggest that a warm pool off the E US serves us badly for a cold winter. The baroclinic gradient tends to be steep here anyway, anomalously warm pooling steepens the gradient and sets up a jet with a lot of energy and which is going tend to move sinuously, keeping the surface flow pretty active - which is what we have right now.

The modifier in our favour at present is cold water in the N Pacific, which serves to reduce energy further upstream, and this might ordinarily favour NW Europe with a cooler than normal winter, but the Norht Atlantic anomalies would have to change first, and, in addition, the warmer pool in the NW pacific simply serves to propagate the jet in the same way as the pooling off Labrador.

If we must have warm pooling in the Atlantic, far better if it would shift further SW. As it is, for all that it is drawing the jet S to the W of the UK, it is spawning too much activity at the surface, and retaining too much enegry aloft, for a cold block to be a serious proposition.

[summer blizzard]

I think you mean an E-W gradient don't you SBz?

As we head into winter I'd suggest that a warm pool off the E US serves us badly for a cold winter. The baroclinic gradient tends to be steep here anyway, anomalously warm pooling steepens the gradient and sets up a jet with a lot of energy and which is going tend to move sinuously, keeping the surface flow pretty active - which is what we have right now.

The modifier in our favour at present is cold water in the N Pacific, which serves to reduce energy further upstream, and this might ordinarily favour NW Europe with a cooler than normal winter, but the Norht Atlantic anomalies would have to change first, and, in addition, the warmer pool in the NW pacific simply serves to propagate the jet in the same way as the pooling off Labrador.

If we must have warm pooling in the Atlantic, far better if it would shift further SW. As it is, for all that it is drawing the jet S to the W of the UK, it is spawning too much activity at the surface, and retaining too much enegry aloft, for a cold block to be a serious proposition.

Yes, i did indeed mean a East to West gradiant.

As for your second point, if we can get a bigger cold pool in the Mediterranian, then lower pressure may not be such a bad thing, as the winter of 1947 showed although we will always be in danger of a zonal flow.

As for the third point, the Aulution Low is serving to draw the polar Jet Stream south in the western USA, which indeed would normally favor a colder than average winter however the Atlantic anomolies are out of sink with this, with a more zonal longwave pattern as opposed to a shortwave pattern.

As for the fourth point, i agree and assuming that the warm anomoly was the same size and strength, i would rather have the center around 40N, 30W.

As the current sea surface anomolies stand, i think we are in danger of a senario similar to that of last year in that we may see a strong Polar Vortex over Canada, causing the Jet Stream to be too strong, on the plus side though, the Tropics are cooler this year, meaning that we should see a more active sub-Tropical Jet Stream.

I will do a detailed post about likely sea surface temperature anomoly trends during Autumn tommorow.

[BLAST FROM THE PAST]

So are we saying there is no timelag? So the SST situation now affects current pattern.

BFTP

[Stratos Ferric]

So are we saying there is no timelag? So the SST situation now affects current pattern.

BFTP

I think it's actually best to say that both of your conditions apply; for all that what we experience is "weather" on the ground, this is just the net product of what is a very complex thermodynamic system. There are "here and now" impacts which are undeniable (e.g. an anomalously warm surface MUST moderate air passing over it more than would nornmally be the case); in addition there are longer term feedback loops, some of which are vaguely understood, many of which I suspect are neither understood nor known.

Edited August 30, 2006 by Stratos Ferric

[parmenides3]

Okay, it's my turn to be dim. I understand that sea surface temperatures make a big difference to weather and weather patterns, but I'm confused about how the anomalies work; can someone please explain it to me? I know what they are, and I know what they show, but I don't understand how they effect our weather.

:unsure: P

[BLAST FROM THE PAST]

Okay, it's my turn to be dim. P

P

Thanks, I like to say confused :unsure: SF ta for that

BFTP

[Stratos Ferric]

Okay, it's my turn to be dim. I understand that sea surface temperatures make a big difference to weather and weather patterns, but I'm confused about how the anomalies work; can someone please explain it to me? I know what they are, and I know what they show, but I don't understand how they effect our weather.

:unsure: P

Don't think about specifics.

In general think of the whole atmospheric system as operating within typical bounds. What an anomaly is is a measurement of some component of that system relative to its periodic norm - we do need to be concerned as to whether that measure is more a leading or a lagging measure, but there's an argument that says that as all parts of the system are connected, a lagging measure in one part of the whole is just a leading measure for the next part downstream. In simple terms, if one of the driving components is varied, then downstream effects will, all other things being equal, vary - so long as these two components genuinely have a cause-effect relationship.

Think about driving your car. Putting your foot on the throttle is the equivalent of an anomalous increase in fuel flow into the engine, the engine responds by creating more energy and so speeds up. Driving around a bend at steady speed you car stays on the road because the frictional effect of the tyres is greater than the centripetal impact of the circular motion, but if the bend suddenly sharpens (i.e. becomes anomalous) then the balance of forces changes.

It may be that on the corner there are trees, and that as we go round the corner the size of tree changes. This too is an example of an anomalous change, but it is quite independent of the system we're considering.

Anomalies are actually helpful in developing understanding of a system, and it is the use of anomalies that lies behind much diagnostic work to understand, for example, strructural failures. In the same way, looking back from particularly unusual climatic or weather events for anomalies upstream can assist in understanding. The main difference between, say, a built structure and the hydrothermal system around the earth is one of scale and complexity, which is why lots of theories abound. There are plenty of examples cited on threads in N-W of pet theories, but often these are unproven hypotheses supported by one, or a few, proponents. The number of genuine cause-effect relationships that work reliably over the long term in global climate is very small.

[parmenides3]

P

Thanks, I like to say confused SF ta for that

BFTP

Just realised that it could have been read to mean that. oops! Unintentional, I promise you.

SF: Sorry, still confused. I do understand about anomalies, but I was hoping for something more specific. If you said, for example, 'the sea here is warm/cool, so the weather there will be warm/cool/wet/dry, fine, I get that. But you are saying ' the sea here is warmer than normal, and there it is cooler than normal, so we can expect...' (is this right?)

To me, this suggests that we have a baseline expectation of weather patterns, according to one set of conditions, and a different expectation if those conditions are outside the norm. What I am hoping for is an explanation of the connection between the two.

P

[summer blizzard]

In less complicated terms, my reading of the sea surface temperature anomoly charts suggests that there is a time lag on synoptics of around three weeks, and that by reading a sea surface temperature anomoly chart, you can extrapolate a probable Jet Stream pattern three weeks ahead assuming that no atmospheric teleconnection patterns overide that signal such as the AO in June.

It must be remembered that the atmosphere is the primary driver of our weather, and not the sea, therefore the sea only drives teleconections such as...

NAO

PDO

WP

EPO

PNA

NP

NOI

However the following signal can overide those teleconnections, these are...

QBO

SOI

AO

MJO

This is why some people are omptimistic about the expected neutral PDO, as sea surface temperature anomolies do not look like they are conductive to a Bartlett High.

So, if we assume that we have a storm near Newfoundland in three weeks time, we must then look at the current anomolies at that time to measure the thermal gradiant in that area as you can not tell how deep a storm will be three weeks in advance, at present, the warm anomoly will produce a massive thermal gradiant in the western Atlantic.

Edited August 30, 2006 by summer blizzard

[parmenides3]

So, in the simplest terms possible, your idea is that the pattern of SSTA on the US Eastern seaboard is an indicator of the likely path of the Jetstream; a baseline, if you like. Is that it?

[summer blizzard]

So, in the simplest terms possible, your idea is that the pattern of SSTA on the US Eastern seaboard is an indicator of the likely path of the Jetstream; a baseline, if you like. Is that it?

Yes.

[parmenides3]

Yes.

Good. Got it. Ta. P

[Stratos Ferric]

Just realised that it could have been read to mean that. oops! Unintentional, I promise you.

SF: Sorry, still confused. I do understand about anomalies, but I was hoping for something more specific. If you said, for example, 'the sea here is warm/cool, so the weather there will be warm/cool/wet/dry, fine, I get that. But you are saying ' the sea here is warmer than normal, and there it is cooler than normal, so we can expect...' (is this right?)

To me, this suggests that we have a baseline expectation of weather patterns, according to one set of conditions, and a different expectation if those conditions are outside the norm. What I am hoping for is an explanation of the connection between the two.

P

It's not that hard and fast I'm afraid, because the system is either non-linear, or else multi-variate. Think about, say, warming climate and the impact on ecosystem. First up you'd say, ooh, warmer weather, longer groind season. So the first impact might be more abundant flora, as these react faster than fauna. The fauna (species A) feeding off the flora then react themselves, but say these are preyed on by another species, species B, what then happens is that species B consumes species A and to the extent that A might have been restraining abundance in the flora, this restraint is now removed. Each relationship here is broadly linear, but some have +ve slope, and others -ve slope, and with different degrees of time lag. It's the equivalent of using straight lines to draw complex diagrams that start to appear to have many curves in them. A complex network of simple relationships leads to a complex network.

We DO have a baseline sense of norm, because we have climatic norms which change only very slowly. For sure the ways of arriving at climatic average are infinite, but the majority come from within a reasonably well defined set of typical outcomes, or an established set of see-saw changes (witness this year's hot dry July and cooler wetter August as an example). These many outcomes presume that the upstream drivers are all, broadly, combining to produce the same sort of drivers as normal.

So, moving forward, say we want to see an unusually cold winter, the logical argument is that we aren't going to see one IF all the drivers are behaving normally (this presupposes we KNOW and can measure accurately ALL of the drivers). Hence, we want to see some anomalous behaviour. Even then, though, it would be possible for different anomalies to net out neutral, but again, the number of ways that this could happen is, for all intents and purposes, infinite.

I say it time and again, if there were any quick solutions to long-term forecasting then far better brains, and far more commercially motivated ones than any we'll find on here, would have got there already. The complexity of the system is almost unknowable, so we can say for sure that there are feedbacks and drivers and eddys in the whole system, but we're a long way from quantifying them reliably such that we can make long term forecasts.

It must be remembered that the atmosphere is the primary driver of our weather, and not the sea, therefore the sea only drives teleconections such as...

AO

NAO

PDO

WP

EPO

PNA

NP

NOI

...

SB, I'd have to pick you up on a couple of things (at least) in that lot.

First, the UK's entire climatic regime is most fundamentally driven by our location within the ocean margin. Weather is transported to us aloft, that's for sure, but the role of the oceans in providing an energy store and transport mechanism is huge. Without the NAD we would have a dramatically different climate. You CANNOT legitimately decouple oceans from atmosphere as they are part of the same hydrothermal system.

NAO is NOT a teleconnection, nor is AO I think. NAO is simply a measure of pressure differential along a line of longitude, and as such it is an "after the event" measure, just like measured temperature is.

There are one or two reasonably well established teleconnections (i.e. there are discenible trends in the behavour of one sub-system and the subsequent behavour of another that leads to an inference that the behaviour is directly consequent), even if the driver mechanisms aren't always well understood. I think I'm right in saying that the southern oscillation is one that genuinely does teleconnect around the globe (well, half way around at least), but there are very few others.

[BrickFielder]

Linking SSTA's to possible future locations of highs and lows is complicated.

Firstly SSTA's can be looked at as having a six month lead time on seasonal conditions. For example certain SSTA pattern which develop in Spring can influence weather in the following winter.

Shorter term then depending on where the warm water is and what time of year it is then you should expect either a baroclinic or barotropic response.

BAROTROPIC- Region of uniform temperature distribution; A lack of fronts. A perfect example of a barotropic environment is the southeast U.S. in the summer or the tropics. Everyday being about the same (hot and humid with no cold fronts to cool things off) would be a barotropic type atmosphere. Part of the word barotropic is tropic. The tropical latitudes are barotropic. There are no fronts in the tropics.

BAROCLINIC- Distinct air mass regions exist. Fronts separate warmer from colder air. In a synoptic scale baroclinic environment you will find the polar jet in the vicinity, troughs of low pressure (mid-latitude cyclones) and frontal boundaries. There are clear density gradients in a baroclinic environment caused by the fronts. Any time you are near a mid-latitude cyclone you are in a baroclinic environment. Part of the word baroclinic is clinic. If the atmosphere is out of balance, it is baroclinic, just as if a person felt out of balance they would need to go to a clinic.

One is baroclinic, shallow and thermal, with anomalously low (high) pressure over anomalously warm (cold) SST (Lindzen and Nigam (1987)). The other is barotropic, involves changes in the surface baroclinicity and in the statistics of the transient eddies (Palmer and Sun (1985)). The latter generally results in anomalously high (low) pressure downstream of a positive (negative) SST anomaly.

These responses can be largely overriden when there is a strong storm corridor like those that exist at times in the north pacific and atlantic.Specifically downstream is usually in relation to the prevalent position of the jetstream long wave patterns. The sensitivity to the SSTA's is also linked to the season or strength of the jet at that time. January is thought to be particularly sensitive to SSTA's whilst February is not.

A stronger response is also forecast where there is a coupled positive and negative SSTA and particular couplets give strong responses. At best local SSTA's give strong signals and depending on other conditions like the the ENSO SSTA's, the MJO, ice and snow extents and stratospheric conditions can be largely over riden for long periods.

Read (Peng et al 1995)(Ferranti et al 1994)(latiff et al 2004)(Frankignoul 2003)

You also might want to read up on the dynamic coupling between the NAO and the north atlantic SSTA Tripole ( or should that be bipole now) .

A final quote

Two types of interactions govern the response: One is an eddy-mediated process, in which a baroclinic response to thermal forcing induces and combines with changes in the position or strength of the storm tracks. This process can lead to an equivalent barotropic response that feeds back positively on the ocean mixed layer temperature. The other is a linear, thermodynamic interaction in which an equivalent-barotropic low-frequency atmospheric anomaly forces a change in SST and then experiences reduced surface thermal damping due to the SST adjustment. Both processes contribute to an increase in variance and persistence of low-frequency atmospheric anomalies and, in fact, may act together in the natural system.

[parmenides3]

Brilliant stuff, guys, thank you. Do I understand it? Err...

One of the advantages of being on a forum, I suppose, is that I can be fairly sure that someone else does understand, so I suppose I will, 'till I can get my head round it, trust others to do the thinking. Your efforts are much appreciated.

P

[BLAST FROM THE PAST]

Brilliant stuff, guys, thank you. Do I understand it? Err...

One of the advantages of being on a forum, I suppose, is that I can be fairly sure that someone else does understand, so I suppose I will, 'till I can get my head round it, trust others to do the thinking. Your efforts are much appreciated.

P

Correct P lots of good stuff going on thanks guys. I will point out that the models are pointing towards SBs reading of the situation a while back...interesting

BFTP

[Stratos Ferric]

Linking SSTA's to possible future locations of highs and lows is complicated.

....

Good post. In essence, the impact of SSTs depends on:

1 - Whether the inertia in the atmosphere is high at the time e.g. a strong jet is less immediately impacted, though magnitude of effect may be enhanced or dampened;

2 - Whether areas of anomaly act to reinforce or counteract each other;

3 - The difference in any case between the ocean surface and the airmass above it. Again, they may attenuate or modify each other (though ocean-air is by far the more powerful flux).

That these impacts are going on simultaneously across the span of the globe makes it very hard to net all the effects to a consequence in any one location.

[pottyprof]

SF.. very interesting stuff.. :o

[summer blizzard]

I have not had much time to post recently however the negative NAO tripole has appeared again, with strong indications of a negative AO and NAO with a pressure build over Greenland and Scandinavia resulting in probable easterly winds araound the 25th.

[summer blizzard]

The cold anomoly to the south of Newfoundland appears to be growing and we may see the development of extra-tropical banding however as i have stated before, September will depend largely on the state of the AO, positive, and Euro High is favoured, negative and we may see quite a southerly tracking Jet Stream.

[beng]

http://weather.unisys.com/surface/sst_anom.html

Interesting SST developments - the focus of the Atlantic warm anomoly has moved further North-West - North of Newfoundland and stretching up the West coast of Greenland. I would think this is starting to look quite good for negative NAO conditions - especially if we get a cold anomoly developing off the East coast of the United States in the next month or so.

[Dawlish]

I have not had much time to post recently however the negative NAO tripole has appeared again, with strong indications of a negative AO and NAO with a pressure build over Greenland and Scandinavia resulting in probable easterly winds araound the 25th.

"Probable" easterly winds around the 25th Sept. Certainly not what the gfs is showing SB! I'd go for a Westerly flow around that time; the direct opposite of what you are proposing, but if you are convinced by this - and your analysis (or, perhaps, wiDoh a dumb swear filter got the better of me) of the establishment of a -ve NAO is interesting - I'll offer you 4/1 against generally Easterly flow across Southern England on 25th Sept. How does that sound?

Paul

Edited September 12, 2006 by Dawlish

[summer blizzard]

I will not take that bet, sea surface temperature anomolies are best used to pick out trends in both teleconnections and synoptics, i try and push the boat out by predicting the weather at a certain time, however teleconnections such as the AO, wich is an atmospheric teleconnection, can overide other signals.

http://www.cpc.noaa.gov/products/precip/CW..._index/ao.shtml

If we look at the teleconnections forecast, we can see that while the PNA is forecast to be positive around that time, the AO is positive meaning that the Jet Stream will rise north resulting in at best a average, zonal westerly flow, or more likely a southerly.

Had the AO being negative, then the NAO would of also being negative and there would of been a strong signal for the Scandianavian High to build westward.