Cryosphere Today 2013 Arctic SIA daily minimum: August poll

[Richard Rathbone]

.

I'm not really minded to average over a few days because the random element that needs averaging gets taken care of in using a long timeseries - .

The measurement technique isn't perfect. You don't remove any of the measurement uncertainty in the June 2014 measurement, by using an average over previous years.

The same applies to how the weather is actually moving the ice about in June 2014. Its similar, but not quite the same as measurement uncertainty. There is no reason to expect that sort of randomness to correlate perfectly between June and September. By using the minimum, rather than a particular September day, you reduce the error associated with random stuff happening on a particular day in September 2014, but in cherrypicking June 23rd, I think you are overfitting.

Detrend the data around the time you are considering. Check the standard deviation on that. That's a source of error that you can either treat as negligible (because the standard deviation is small) or you can diminish by smoothing the June curve in 2014 rather than picking the value on a particular date. You can't get rid of it by cherrypicking which day in June over the past however mnay years was least affected by it. Using a long time series protects you against a severely overoptimistic error bound from your cherry pick, but doesn't change that its a cherry pick giving you an overoptimistic error bound.

I think daily CT area anomaly is bouncy enough that a simple smoothing would be a modest but worthwhile improvement, but I haven't calculated the variance to prove it.

Its one thing to do the calculation and keep it to yourself. Its another to put it out there when everybody reckons you are wrong and stick by it.

[ChrisReynolds]

Now I understand what you're saying Richard. I'm not sure what gain I'd make though. I really don't know enough probability theory to get to grips with making a proper estimate of probability associated with the choice of bounds of the prediction. In choosing the multiplier of sigma for my 2013 prediction I merely tried different numbers until the hindcast prediction gave a certain percentage of success - not a sound option with only 2007 to 2013.

I've saved a link to your comment near my workings on the spreadsheet to consider when I get back to this. But for the next several days I'm going to get my head down about the atmosphere post 2007 and this year.

[Richard Rathbone]

Do you intend to use the method come what may in June 2014? Or are you going to wait and see what June 2014 looks like? If you are going to wait and see, there's not so much to gain from removing some of the possible variance due to June 23rd being an outlier in the method. You are controlling it by seeing the data before making your prediction.

If you intend to have something on June 1st 2014 that anyone could plug the number into come June 23rd and call it the Reynolds projection , its a bit more important to control the randomness associated with the start point.

[ChrisReynolds]

Well I have a long time to consider...

As for the 'Reynolds projection' - now that would be taking a small gloat to a pompous and preposterous level. Frankly it would be embarrassing.

[Pmt111500]

'to a pompous and preposterous level.', I just had to check on 'Reynolds projection' and this came up: http://www.allmusic.com/album/astral-projection-mw0000066153 , but really you're imho about the down-to-earthest fellow in here so I thought You might appreciate the contradiction.

[Richard Rathbone]

Frankly it would be embarrassing.

 

Its a lot harder to put together a technique that someone else can use without embarrassment than one you can use without embarrassment. As some of the inventors of techniques used in cricket this summer can testify. To err is human, but to really make a mess you need a Decision Review System.

[ChrisReynolds]

'to a pompous and preposterous level.', I just had to check on 'Reynolds projection' and this came up: http://www.allmusic.com/album/astral-projection-mw0000066153 , but really you're imho about the down-to-earthest fellow in here so I thought You might appreciate the contradiction.

There's a further level of contradiction in that I'm not generally into guitar music - although it has a place in my collection (e.g. Killing Joke). I often work to Progressive House/Trance. But this is possibly my favourite track ever:

[Pmt111500]

it appears http://arctic.atmos.uiuc.edu/cryosphere/timeseries.anom.1979-2008 has stopped updating. there could be some use to make a thread of available sources of arctic/antarctic data spite the republican ideology that the poor should not recieve affordable care if they want to. IJIS of JAXA and DMI arctic at least seem to work
http://www.ijis.iarc.uaf.edu/seaice/extent/plot.csv
http://ocean.dmi.dk/arctic/index.uk.php

[ChrisReynolds]

They must be using NSIDC data because NSIDC extent hasn't updated from around the same time. The problem is the US Government shutdown.

[Wipneus]

CT may be back, but not without errors:

 2013.786 -0.9914432 5.549588 6.541031
 2013.789 -0.9373526 5.713190 6.650542
 2013.789 -1.0399481 5.713190 6.753138
 2013.792 -0.9930274 5.856593 6.849620


Any graph/computation that assumes every line is another day will be in error. Some of mine do, some don't.

[ChrisReynolds]

Thanks Wipneus,

I'm in the process of rebuilding my sea ice spreadsheet from scratch. There are other days when this happens (two or three instances I think), for example:

2009.4219   -0.4995524   10.209259   10.7088118
2009.4274   -0.6721296   9.9593401   10.6314697
2009.4274   -0.6045403   9.9593401   10.56388
2009.4302   -0.5670587   9.9429379   10.5099964

In that case it works if I manually edit the second 2009.4272 to be day 157.

[Neven]

Does CT SIA spreadsheets need to be rebuilt from scratch, or is that a personal pastime of yours, Chris? I still have to update my IJIS SIE spreadsheet to V2.

[Wipneus]

CT may be back, but not without errors:

 2013.786 -0.9914432 5.549588 6.541031
 2013.789 -0.9373526 5.713190 6.650542
 2013.789 -1.0399481 5.713190 6.753138
 2013.792 -0.9930274 5.856593 6.849620

Corrected on a late Sunday evening:

 
 2013.7863  -0.9914432   5.5495882   6.5410314
 2013.7891  -0.9373526   5.7131896   6.6505423
 2013.7917  -0.8965446   5.8565931   6.7531376
 2013.7946  -0.9335849   5.9160357   6.8496203

[ChrisReynolds]

Does CT SIA spreadsheets need to be rebuilt from scratch, or is that a personal pastime of yours, Chris? I still have to update my IJIS SIE spreadsheet to V2.

I built my last one years ago, and there's no space for more years. I'm also unhappy with the layout being messy, so I want to include some features of the last one in this new one in a tidier way.

[Wipneus]

Thanks Wipneus,

I'm in the process of rebuilding my sea ice spreadsheet from scratch. There are other days when this happens (two or three instances I think), for example:

2009.4219   -0.4995524   10.209259   10.7088118
2009.4274   -0.6721296   9.9593401   10.6314697
2009.4274   -0.6045403   9.9593401   10.56388
2009.4302   -0.5670587   9.9429379   10.5099964

In that case it works if I manually edit the second 2009.4272 to be day 157.

FWIW, for those days here is area calculated from NSIDC gridded concentration data, using, what I think, is the most likely CT method:


 20090601 10.204885
 20090602 10.080988
 20090603 10.016921
 20090604   9.934614

[ChrisReynolds]

Thanks Wipneus.