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Blessed Weather

Teleconnections - Interactions and Impact

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On 18/01/2020 at 10:43, Blessed Weather said:

Hope not - a strongly positive IOD seems to be a winter killer for the UK (if cold/snow is your preference). Here's the index since 1982 showing 3 previous strong events in 1994, 1997 and 2006.

1816674263_IODIndex1982toDec2019.thumb.gif.3518c71ae1a3398fa7498ee9910c0e37.gif

Source: https://stateoftheocean.osmc.noaa.gov/sur/ind/dmi.php

And the weather in the winters that followed?

1994/95 - Very mild with a 3-month winter average CET of 5.9C. The summer of 1995 saw a record breaking heatwave.

1997/98 - Very mild with a 3-month winter average CET of 6.1C. Record breaking winter warmth for the UK and Europe.

2006/07 - Very mild with all 3 winter months CET above long term average. This article from Philip Eden:

 

Very interesting, but it can also tie into this other post -

 

On 20/01/2020 at 18:05, Kirkcaldy Weather said:
 
 

A couple of years back after speculation that the 'cold blob' would increase risk of early frosts and a colder winter for 2018, a rough analysis suggested that a negative May/June SST anomaly for an arbitrary 45-60°N, 10-50°W actually leads to a milder November and December, similar to the Atlantic tripole findings of Rodwell and Folland et al -

https://www.netweather.tv/forum/topic/90431-uk-first-ground-and-air-frost-watch-season-2018-2019/?do=findComment&comment=3908027

The source area was not optimised for correlation and also ignored any wider tripole which may explain that the cooler the blob area, the more pronounced the effect and milder the December. For the 12 coldest May/June average blob temperatures since 1950, there was only one colder than average December, 1976 (not 2009 as wrongly stated originally).

A simple 2nd order polynomial fit for the SST data 1950-2017 gives a CET prediction of 6.0°C for Dec 2018 (actual 6.9) and 5.76°C for Dec 2019 (actual 5.8) so that's only 1 colder than average December from the 14 coldest 'blobs' and 8 of these are 6+ degC.

At the extreme, the second coldest blob gave the second warmest December, 1974, and the coldest gave the warmest, 2015....which brings us back to the positive IOD years. 1994 fits the pattern well with its 6.4°C December following the 4th coldest blob. 1997 and 2006 however are very much in the 'warm blob' territory. A fuller analysis taking into account patterns of SST and detrending temperatures may give better results, but there do appear to be reasonable predictions available at 6/7 months in advance.

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3 hours ago, Interitus said:

Very interesting, but it can also tie into this other post -

 

A couple of years back after speculation that the 'cold blob' would increase risk of early frosts and a colder winter for 2018, a rough analysis suggested that a negative May/June SST anomaly for an arbitrary 45-60°N, 10-50°W actually leads to a milder November and December, similar to the Atlantic tripole findings of Rodwell and Folland et al -

https://www.netweather.tv/forum/topic/90431-uk-first-ground-and-air-frost-watch-season-2018-2019/?do=findComment&comment=3908027

The source area was not optimised for correlation and also ignored any wider tripole which may explain that the cooler the blob area, the more pronounced the effect and milder the December. For the 12 coldest May/June average blob temperatures since 1950, there was only one colder than average December, 1976 (not 2009 as wrongly stated originally).

A simple 2nd order polynomial fit for the SST data 1950-2017 gives a CET prediction of 6.0°C for Dec 2018 (actual 6.9) and 5.76°C for Dec 2019 (actual 5.8) so that's only 1 colder than average December from the 14 coldest 'blobs' and 8 of these are 6+ degC.

At the extreme, the second coldest blob gave the second warmest December, 1974, and the coldest gave the warmest, 2015....which brings us back to the positive IOD years. 1994 fits the pattern well with its 6.4°C December following the 4th coldest blob. 1997 and 2006 however are very much in the 'warm blob' territory. A fuller analysis taking into account patterns of SST and detrending temperatures may give better results, but there do appear to be reasonable predictions available at 6/7 months in advance.

How can the cold blob turning into a warm one then?

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5 hours ago, damianslaw said:

How can the cold blob turning into a warm one then?

This graph shows the average May/June SST for the arbitrary central north Atlantic region from 1950-2019 -

cb.thumb.png.6c9f34c34b8ae43467ee8f80e02b9e89.png

Clearly, there has been a downward trend counter to warming elsewhere, which represents the 'cold blob'. But the decrease is not monotonic and displays much interannual/interdecadal fluctuation. Primarily the temperatures are a response to atmospheric conditions, precipitation, evaporation, insolation etc which vary with the NAO. On top of this there is infeed of currents of varying temperature and salinity into the sub-polar gyre and levels of winter deep convection overturning the static stability. To show the contrasts in temperature compare the coldest year 2015 at 9.568°C leading to the record December CET - just five years earlier the cold December was preceded by the 5th warmest SST in the series at 11.0475°C.

Here is an interesting paper comparing the winters 2009/10 and 2010/11 and highlighting the probable importance of SST anomalies in the latter -

Quote

North Atlantic SST Anomalies and the Cold North European Weather Events of Winter 2009/10 and December 2010

Abstract

Northern Europe experienced consecutive periods of extreme cold weather in the winter of 2009/10 and in late 2010. These periods were characterized by a tripole pattern in North Atlantic sea surface temperature (SST) anomalies and exceptionally negative phases of the North Atlantic Oscillation (NAO). A global ocean–atmosphere general circulation model (OAGCM) is used to investigate the ocean’s role in influencing North Atlantic and European climate. Observed SST anomalies are used to force the atmospheric model and the resultant changes in atmospheric conditions over northern Europe are examined. Different atmospheric responses occur in the winter of 2009/10 and the early winter of 2010. These experiments suggest that North Atlantic SST anomalies did not significantly affect the development of the negative NAO phase in the cold winter of 2009/10. However, in November and December 2010 the large-scale North Atlantic SST anomaly pattern leads to a significant shift in the atmospheric circulation over the North Atlantic toward a NAO negative phase. Therefore, these results indicate that SST anomalies in November/December 2010 were particularly conducive to the development of a negative NAO phase, which culminated in the extreme cold weather conditions experienced over northern Europe in December 2010.

https://journals.ametsoc.org/doi/full/10.1175/MWR-D-13-00104.1

For reference, the 2009 May/June SST was cooler than average at 10.16°C which should have tended towards a warmer December.

Edited by Interitus

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19 hours ago, Interitus said:

This graph shows the average May/June SST for the arbitrary central north Atlantic region from 1950-2019 -

cb.thumb.png.6c9f34c34b8ae43467ee8f80e02b9e89.png

Clearly, there has been a downward trend counter to warming elsewhere, which represents the 'cold blob'. But the decrease is not monotonic and displays much interannual/interdecadal fluctuation. Primarily the temperatures are a response to atmospheric conditions, precipitation, evaporation, insolation etc which vary with the NAO. On top of this there is infeed of currents of varying temperature and salinity into the sub-polar gyre and levels of winter deep convection overturning the static stability. To show the contrasts in temperature compare the coldest year 2015 at 9.568°C leading to the record December CET - just five years earlier the cold December was preceded by the 5th warmest SST in the series at 11.0475°C.

Here is an interesting paper comparing the winters 2009/10 and 2010/11 and highlighting the probable importance of SST anomalies in the latter -

https://journals.ametsoc.org/doi/full/10.1175/MWR-D-13-00104.1

For reference, the 2009 May/June SST was cooler than average at 10.16°C which should have tended towards a warmer December.

Interesting reading, when did the tripole develop then in 2009, through the summer and autumn? normally its SST values in May that indicate likely negative NAO or not.. I think the El Nino modoki was a strong factor for the cold winter of 09/10, it did start mild after a very mild November as well..

2010 was cold throughout with lots of northern blocking which will have helped with warm uppers over N Atlantic.

A blocked spring helps I think with mid atlantic heights, 1995 brought this, and we saw a tripole in winter of 95/96.. did 2005 do the same?, tripole again in winter 2005/2006.

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On 04/02/2020 at 18:36, mushymanrob said:
visual-cortex-globe-temperatures.png
WWW.METOFFICE.GOV.UK

The Madden-Julian Oscillation is characterised by an eastward spread of large regions of enhanced and suppressed tropical rainfall, mainly...

 

I'm going to throw this one in here as well as it has some very good animations to show the different phases.

MJO_610_0.png
WWW.WEATHERNATIONTV.COM

[The surface and upper-atmosphere structure of the MJO for a period when the enhanced convective phase (thunderstorm cloud) is centered across the Indian Ocean

 

 

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World Climate Service tweet 13th Feb:

This is getting ridiculous - peak AO index values in recent ECMWF HRES (10-day) runs:
Feb 12 00Z +6.4
Feb 12 12Z +7.3
Feb 13 00Z +7.6
We've capitulated and expanded the scale on our AO graphics to accommodate the extreme. 1950-present record (set 3 days ago) is +6.3

347725020_ECMWFAOforecast13Feb.thumb.jpg.448981e2a7d6000536b0e792abf56019.jpg

Source: Twitter @WorldClimateSvc

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