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Author Topic: Variations in lag between AO and ISST  (Read 5066 times)

Ice Cool Kim

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Variations in lag between AO and ISST
« on: April 21, 2013, 01:12:36 AM »
I'd noticed some apparent slippage in other plots so I thought I'd have a closer looks at the lag between AO and temps.

Melting period follows AO and rate of change of extent follows temps so the different may be informative.

Here I have chosen segments of AO that have about the same phase and with physical variations that allow identification of the alignment. No other ulterior motive just exploring.

Since AO is one of those detrended EOF thingies I have shifted the last two segments up a bit in order that they follow ISST, to better align the phase.

No changes were made to vertical scale.
« Last Edit: April 22, 2013, 12:27:26 PM by Ice Cool Kim »

Ice Cool Kim

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Re: Variations in lag between AO and ISST
« Reply #1 on: April 21, 2013, 01:25:43 AM »
Observations.

AO and ISST are very close in amplitude before 1997 but a notable adjustment to phase of 6 months was needed.

>1997 there is still enough resemblance to align the two but they are now notably different.

Large dip on AO at end of 2010 is notable and uncharacteristic difference between the two.


hadISST shifted up by its "neutral" value I found here : http://forum.arctic-sea-ice.net/index.php/topic,234.0.html


Phase lag of AO was quite considerable where there was a lot of thick ice. Probably logical, ice slow to transmit heat , less open water etc.

Slight reversal in final section despite ice remaining thin and much open water. Is this related to flattening of rate of change, why?

Poor correlation pre-1980 seems surprising in view of the very tight correlation later.  Perhaps this is due to both records being less accurate in the pre-satellite era.

Without the vertical offset of the last two sections AO stays centred on the line.

« Last Edit: April 22, 2013, 12:27:55 PM by Ice Cool Kim »

frankendoodle

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Re: Vaiations in lag between AO and ISST
« Reply #2 on: April 21, 2013, 01:54:29 AM »
Observations.

AO and ISST are very close in amplitude before 1997 but a notable adjustment to phase of 6 months was needed.


May I ask why this adjustment was needed? I mean no offense, I'm sure you have your reasons, but it seems a little ad hoc.

Ice Cool Kim

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Re: Vaiations in lag between AO and ISST
« Reply #3 on: April 21, 2013, 02:20:39 AM »
It was needed for the two sections to remain in phase.

ad hoc means done for a specific purpose and that was the purpose. The exercise is to get rough and ready look at how the phase changes over the record.

It's not a step change but I don't think it is a gradual linear slide either. There seems to be a notable shift just before the 1990 rise. I could probably have split the blue section again but I did not want to be too piecemeal about it.

It would be interesting to have some fancy technique to plot the phase difference as a function of time , the cause may become more apparent.



Ice Cool Kim

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Re: Vaiations in lag between AO and ISST
« Reply #4 on: April 21, 2013, 02:55:47 AM »
Since AO is running about 8m ahead of ISST now it may give a clue as to what will happen in this melting season. (AO is used for short term prediction in meteorology).

That would suggest that it will be slightly cooler than 2012 just past its peak.

http://forum.arctic-sea-ice.net/index.php/topic,234.0.html

rate of change of extent is small but negative at the moment and looks like it's also turned and will increase a bit in magnitude. So I expect a new record low but nothing dramatic.

http://forum.arctic-sea-ice.net/index.php/topic,174.msg2880.html#msg2880

Typical alternating pattern in length of melting season, would suggest a slight increase this year.

That's about all I'd want to read into those plots, especially since some long standing patterns seem to be changing direction since 2010.

« Last Edit: April 21, 2013, 04:21:27 AM by Ice Cool Kim »

Ice Cool Kim

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Re: Vaiations in lag between AO and ISST
« Reply #5 on: April 21, 2013, 10:48:25 AM »
Interesting article on Curry's site where this Neven's "well respected" site gets a fleeting mention.

http://judithcurry.com/2013/04/10/historic-variations-in-arctic-sea-ice-part-ii-1920-1950/

Quote
“The sources used to compile the HadISST data set are given by Rayner et al. [2003]. Up to 1978, HadISST used the Northern Hemisphere Walsh fields [Walsh and Chapman, 2001] as its main data source, which in turn relied upon ice charts from a number of different sources to locate the sea ice edge. However, prior to satellite observations, none of these charts provided coverage in the Russian Arctic further east than the Kara Sea [Kelly, 1979; Vinje,2001]. Where no sea ice edge data were available, a baseline climatology was used. Such instances are apparent in Figure 8 where the green data points are constant from year to year in the early part of the record.”

Confirms my earlier comment about probably cause for the poorer correlation in pre-sat. era.

Neven

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Re: Vaiations in lag between AO and ISST
« Reply #6 on: April 21, 2013, 11:10:30 AM »
This article was briefly discussed here.
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Ice Cool Kim

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Re: Variations in lag between AO and ISST
« Reply #7 on: April 21, 2013, 11:30:45 PM »
I've had another look at this and inserted another break as I suggested above.

It does seem like there were clear, punctual phase shift events, rather than a steady drift. At least in the well correlated section.

The later splits are less well defined since the correlation is less consistent.

 split dates in ISST timescale :  1988.8 1994.5 1998 2006.8

There may be justification for a fifth break at 2003.5 , the phase at the bottom of that rise shifts off. Though with the lack of features it would be hard to align the phase of that segment.


It may be worth looking for an event that cause the first two which are clearly defined.
« Last Edit: April 22, 2013, 12:29:27 PM by Ice Cool Kim »

Ice Cool Kim

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Re: Vaiations in lag between AO and ISST
« Reply #8 on: April 21, 2013, 11:52:24 PM »
The phase shifts all seem to happen just before a notable rise in temperature. Three also match notable spikes in the length of melting season:

http://forum.arctic-sea-ice.net/index.php/topic,174.msg2880.html#msg2880

I may be starting to see a pattern here which would lead to another phase shift around 2012.5, though it will need another year's data to see how ISST peak defines.

If that marks the peak of another rise in ISST it could be trouble.

The wildcard is that the last phase shift was in the opposite direction. It remains to see what effect that has.
« Last Edit: April 22, 2013, 12:50:56 AM by Ice Cool Kim »

Ice Cool Kim

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Re: Variations in lag between AO and ISST
« Reply #9 on: April 22, 2013, 09:23:05 PM »
wikipedia:

On March 13, 1989 a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds

Seventeen major flares erupted on the Sun between 19 October and 5 November 2003

In view of the filtering applied and the crudeness of the detection of the date of the phase change that seems to match two of my dates of phase shift.

Certainly. the most significant geomagnetic storm of the satellite era seems to be a fairly obvious candidate for the 1989 event.


http://www.sciencedaily.com/releases/1998/09/980928072950.htm
" a major geomagnetic storm began late on Sept. 24 [1998]... The geomagnetic storm measured 8.6 on a scale of 0 to 9 used to measure geomagnetic storm intensity. "


http://news.discovery.com/space/solar-radiation-storm-largest-since-2003-120125.htm
re. Jan 23, 2012
“Earlier, it was stated that the current Solar Radiation Storm was the largest since May 2005,” said Tuesday’s announcement on the NOAA Space Weather Prediction Center‘s Facebook page. “After the arrival of the CME earlier today … this is now the largest Solar Radiation Storm since October 2003 (The Halloween Storms).”

« Last Edit: April 22, 2013, 09:36:56 PM by Ice Cool Kim »