Sea Surface Temperature And Sea Ice Trends(2)

[andy_leics22]

Well yeah the La Nina is losing its strength now, the latest weeklies shows the 3.4 zone is now down to -1.0C, just borderline moderate, where interesting -ve NAO's are strongly favored which is interesting given the northerly airflow last weekend and also the wanten of the models to develop northern blocking again.

La Ninas nearly always decay during Spring its what happens in late summer that should prove far more interesting.

I'm sorry to sound dumb Kold, but I have read a fair bit about La Nina on this forum in the past and how it can affect our winters... Could you explain what La Nina is and how is can affect us and in what way it affects us? Like for instance.. Strong La Nina could mean we have a mild Atlantic dominated winter or not...

Hope you can clear it up for me mate

[Jack Wales]

the latest weeklies shows the 3.4 zone is now down to -1.0C.

La Ninas nearly always decay during Spring its what happens in late summer that should prove far more interesting.

Hi Kold, can you (or anyone) provide me with a link to the weekly mei values please?

I agree that El Nino is dissipating and at this rate we should be ENSO neutral by May so I hope this will prevent a washout summer a la 2007. It will be interesting to see what happens after the summer but with a W'ly QBO I'm not holding out too much hope!

Cheers,

JW

[Jack Wales]

I'm sorry to sound dumb Kold, but I have read a fair bit about La Nina on this forum in the past and how it can affect our winters... Could you explain what La Nina is and how is can affect us and in what way it affects us? Like for instance.. Strong La Nina could mean we have a mild Atlantic dominated winter or not...

Hope you can clear it up for me mate

Andy, Kold will be able to give you a far more technical reply but for what it's worth, La Nina is a negative Enso event (cold SST's) over the equatorial Pacific. The equatorial Pacific is split into a number of regions, of which region 3.4 is deemed to have the greatest correlation with our weather. This is due to the large HP cell generated in the central/northern pacific causing the PFJ to surge north towards Alaska then plunge southward through the N American continent resulting in cold conditions across Canada and north east USA. The cold air meets the tropical maritime air in the Atlantic causing a strong thermal gradient stimulating the PFJ and locking down the Polar Vortex over Greenland thus overriding any other teleconnections. This winter has been a classic example of this as we have seen numerous vigorous areas of Low Pressure pass close to or through the UK.

In layman's terms, a moderate or strong La Nina (or El Nino) correlate with milder zonal winters over W Europe. The chances for colder winters in our parts are heightened when the ENSO is weakly +/- or neutral.

The CPC site contains some useful info...

ENSO

El Nino / La Nina

Hope this helps.

Edited March 31, 2008 by Jack Wales

[andy_leics22]

Andy, Kold will be able to give you a far more technical reply but for what it's worth, La Nina is a negative Enso event (cold SST's) over the equatorial Pacific. The equatorial Pacific is split into a number of regions, of which region 3.4 is deemed to have the greatest correlation with our weather. This is due to the large HP cell generated in the central/northern pacific causing the PFJ to surge north towards Alaska then plunge southward through the N American continent resulting in cold conditions across Canada and north east USA. The cold air meets the tropical maritime air in the Atlantic causing a strong thermal gradient stimulating the PFJ and locking down the Polar Vortex over Greenland thus overriding any other teleconnections. This winter has been a classic example of this as we have seen numerous vigorous areas of Low Pressure pass close to or through the UK.

In layman's terms, a moderate or strong La Nina (or El Nino) correlate with milder zonal winters over W Europe. The chances for colder winters in our parts are heightened when the ENSO is weakly +/- or neutral.

The CPC site contains some useful info...

ENSO

El Nino / La Nina

Hope this helps.

That helped a lot, thanks

[Glacier Point]

Monthly changes in Atlantic SSTAs suggest a strong cooling off in the SW and eastern Atlantic:

Sub surface data also suggests no great warm pool mid Atlantic and, with the current synoptics (cut off lows, northerly flow and strong tropical convection), expect to see a SSTA signal for displaced high pressure belts this Summer.

http://www.ecmwf.int/products/forecasts/d/...e!30W!/

The key question will be - displaced northward (+AO) or southward (-AO) ?

[BLAST FROM THE PAST]

Monthly changes in Atlantic SSTAs suggest a strong cooling off in the SW and eastern Atlantic:

Sub surface data also suggests no great warm pool mid Atlantic and, with the current synoptics (cut off lows, northerly flow and strong tropical convection), expect to see a SSTA signal for displaced high pressure belts this Summer.

http://www.ecmwf.int/products/forecasts/d/...e!30W!/

The key question will be - displaced northward (+AO) or southward (-AO) ?

Southward. I think we could get a fair bit of rain again this summer and not a particularly warm one either.

BFTP

[BLAST FROM THE PAST]

The cooling Atlantic?

BFTP

[Hiya]

The cooling Atlantic?

BFTP

Not many warm anoms at all compared with 5 years ago

[johnholmes]

its called swings and round abouts!

[Cal]

its called swings and round abouts!

Thought it was swings & seesaws

[BLAST FROM THE PAST]

its called swings and round abouts!

Climbers and sliders

BFTP

[summer blizzard]

Sea surface temperature anomolies showing a lot of negative anomolies at the moment, though for the UK they seem to indicate high pressure over Europe and low pressure to the north west for around the 15th.

[BrickFielder]

Typically a negative extratropical SST anomalies will be associated with stronger than normal surface westerlies above (and straddled by a pair of sea level pressure anomalies, a cyclone poleward and an anticyclone equatorward). The opposite is true for warm SST anomalies.

(From ATMOSPHERIC GCM RESPONSE TO EXTRATROPICAL SST ANOMALIES: SYNTHESIS AND EVALUATION by Peng et al)

This would give us something like the following.

This pattern will tend to move north as the jet stream goes north. In terms of temperatures then you should expect an above average CET with well above average night time temperatures (cloudy), cooler day time temperatures and more frequent wet periods (rainy days rather than downpours).

The problem is that this is not really the dominate pattern and will only come into play when la nina and the pacific pattern is not dominate. Unfortunatly we can see the typical la nina pattern from todays jet forecast. Cut off low comming off the US coast preventing any typical azores high forming.

In theory then we should get drier and wetter periods as the jet migrates northwards in spring and then again as it migrates southward during autumn.

The problem is that there is likely to be disruptions to the patterns from MJO events, Hurricanes/ Cyclones and I do not think we will see the typical la nina summer.

For those who think la nina is on its way out then I would point out that global angular momentum is still low and just below the surface of the warm anomaly of the coast of south america is more cold water (See SubSurface charts) . It is just too early to tell.

CPC ENSO Forecast

Late snow melt across Siberia this year is likely to give a wet asian monsoon and by nature of Rossby wave propagation nothwestward from the monsoon region this should give descending air over the Eastern Meditteranean. So we might be looking at high pressure over the eastern med and low pressure towards the western med for the early part of the monsoon and then switching the other way round later on. It all depends on which signal is strongest at any one time and it would be unusual if north atlantic sea temperatures had the dominate signal for most of the summer.

[Glacier Point]

Hypothetically, reanalysis of NH oceanic (seasonally lagged) patterns supports the notion of a cut off low in the western Atlantic although the western European response is a ridge:

SSTA pattern observed Feb - present:

SSTA pattern composite matches:

Predicted baroclinic response to SSTAs at H500 for May:

I think we will continue to see the Nina vs. tropical forcing in the Indian Ocean for at least the next 2 months setting the overall pattern. This I think will not be bad for the UK.

[BrickFielder]

What is noticeable there is the trough into the US. and downstream ridge towards greenland. I take these to be typical la nina signals.

What I am not sure about is the placement of the low over northern russia. Its been quite cold up there this winter and you might expect high pressure to linger on. What do you think?

[Lettucing Gutted]

What is noticeable there is the trough into the US. and downstream ridge towards Greenland. I take these to be typical la nina signals.

What I am not sure about is the placement of the low over northern Russia. Its been quite cold up there this winter and you might expect high pressure to linger on. What do you think?

It is not unusual for cold locations such as Russia to be overlaid by an upper level low. In addition to adiabatic cooling associated with deep occluding lows the 500HPA surface can also be lowered by a deep cold airmass associated with either cold air advection or radiative cooling associated with a cool high. A similar thing happens over Greenland and Antarctica when the Polar Vortex is strong.

Edited April 25, 2008 by Craig Evans

[Glacier Point]

What is noticeable there is the trough into the US. and downstream ridge towards greenland. I take these to be typical la nina signals.

What I am not sure about is the placement of the low over northern russia. Its been quite cold up there this winter and you might expect high pressure to linger on. What do you think?

The Russian low might be a good example of a long-established ocean-atmosphere coupling given that we've been under Nina conditions for some time.

Composites for mature (fading) Nina and strong -ve anomalies for ENSO region 4 support the idea of the low:

.. as do composites for weak QBO:

.... as do composites for the current upper zonal wind anomaly:

which makes sense given that weak zonal wind anomalies over the Pole support a stronger Arctic High and displaced cold air pool over the coolest landmass.

You'll note the implications for the UK with some of that cold air over Greenland driving a ridge from the SW approaches over the UK towards S. Scandinavia.

Edited April 25, 2008 by Glacier Point

[BLAST FROM THE PAST]

The cooling Atlantic?

BFTP

Thats the coolest I've seen waters around the UK for sometime and the Atlantic in general...maybe why the heatwave became not a heatwave recently.

BFTP

[Jack Wales]

Thats the coolest I've seen waters around the UK for sometime and the Atlantic in general...maybe why the heatwave became not a heatwave recently.

BFTP

That's probably due to the southerly tracking jet of recent times. I expect values to catch up somewhat around our shores towards the end of the month.

What's also interesting is the sub surface anomaly in ENSO regions 1 & 2, this has gone from being negative (-3 in places) to highly positive (+5C in places) over the last few weeks. Could this be a first sign of a developing El Nino? Although this may enhance our chances of late summer/autumn warmth, it doesn't bode well for winter 2008/09 for cold lovers.

[summer blizzard]

Cold anomolies ahve now banded in the Atlantic, probably enhancing the -NAO signiture, lets hope we dont get a -AO.

[Jack Wales]

Yes, the SST signal at the moment could favour a greenland high, lets hope not!

[BLAST FROM THE PAST]

Yes, the SST signal at the moment could favour a greenland high, lets hope not!

Yes back end of this month. Also no I don't think an El Nino will develop but neutral values maybe observed. However, watch the western side of S America looks like another cold band developing.

BFTP

[kold weather]

Well this week has seen the La Nina strengthen a little now with the 3+4 region at -0.8C but its jst waxing and wanning at the present with no real changes occuring, its just slowly changing and responding the easterly trade winds strength at the time.

[SMU]

The current SSTA looks nice vis a vee the Meto May to Winter NAO Forecast-

S

[BLAST FROM THE PAST]

The current SSTA looks nice vis a vee the Meto May to Winter NAO Forecast-

S

Ah at last a judgement call. Steve I thought it looked pretty favourable [for NAO set up] but am by no means any sort of authority on this...I leave that for you tech guys. To refresh folk and me would you give brief summary of current situ and possible indications.

regards

Fred