Archive for April, 2011

How polar ice is modulated by the sun

April 30, 2011 9 comments

What follows here is a demonstration of how earth orbit shapes Arctic ice and in a later post I intend to show how this may well relate to palaeoclimatology shown in ice cores.

You will have seen the plots of Arctic sea ice. I am going to use one dataset here, which one is unimportant, others give the same answer.

Arctic sea ice extent, monthly data

Read more…

Categories: analysis, filtering, sea ice, solar

Epica Vostok resampled composite

April 27, 2011 Comments off

I won’t say much here now, busy.

This seems to confirm a huge date mistmatch between the two sets of ice core data.

This is a deliberately large plot. Contact me if you need data or help.

Composite of signal processing resampled data from two ice cores

Simplest way to provide data is an export to XLS format of work, warts and all.

Contains usable resampled data and originals

Added later, easiest way to provide data is export to XLS, is scruffy workfile


Categories: analysis, filtering, Ice core

Vostok ice core, part 2

April 26, 2011 Leave a comment

See part 1 if you haven’t.

Seemed a good test to see if I could reproduce the temperature vs. CO2 lead lag result but using signal processing, data resampling. Turns out  the CO2 data is even worse than the isotope ratio temperature data, fewer data points and sampled at different dates.

Easy. I applied identical processing to both datasets and then figured out how to time shift one of them. To my surprise there is a very high correlation, r2=0.82, at least given the preprocessing used. The quick and dirty way to do the time shift was apply an offset at the decimate stage, simply picks off data at a different point. (this is valid)

If I have done this right it is about 1,500 years for best fit of rise and fall. I then aligned the datasets and plotted (Y axis reacaled and offset CO2 by hand so the data roughly matches on one scale)  for an eyeball.

Time co-incident plot of temperature and CO2

There is obviously a lot going on but there it is visibly on one plot.

A net dig shows a work by Jo Nova (know the name, no idea who she is)

That says 800 years and seems to cite others.


Categories: analysis, filtering, Ice core

Vostok ice core, part 1

April 26, 2011 Leave a comment
An ongoing development is better handling irregularly sampled data. This is a very hard problem with no pure solution.
After a lot of investigation and experimentation I have concluded that NDFT/NDFT are of little use, solve nothing, kicks straight back into the input data must be good. Usually involved is approximating and other heuristics.
Looks hard. Run away.

Raw data overlaid with a resampled dataset

For what I am doing a good solution is fix up the dataset using signal processing, kind of trivial, although it will seem black magic to outsiders. (why no blue, pink, white, transparent magic?)
A key is keeping the human brain in the loop, each case is likely to be different with no one size fits all.
I’ve coded up the hard part for a human as an extension of one software package.
Seems to work nicely, as above, the test dataset. Vostok original data sampling ranges from 60 through 600 years.
An XLS with the original data and resample dataset is here vostoke-temperature-a
The dataset is now clean and trivial for normal tools.
And for those who like first difference…
Hiding anything? Nope. The 1st diff does of course have high frequency noise but is surprisingly small. Only clear term in the part not shown is ~4044y. No idea what that is if anything.
More to be done, always is.
Categories: analysis, filtering, Ice core

Length of Day, modelling the lunar and annual effect

April 14, 2011 1 comment

As a result of helping someone out with lunar effects in Earth length of day I wondered if a slightly more comprehensive version would work.

The result  is an interactive spreadsheet which might be useful.

I would not usually  produce such a monster, this is an xls >30Mbyte but it does include reconstruction of the lunar LoD signal, subtraction from the raw LoD and decimation for plotting. It is live, you can turn on or off individual terms/factors and see the effect.

This needs a great deal of explanation, codas, and so on.

For now here is the file lod-work

Do not try this unless you have a fairly large computer. Checked it works with gnumeric, openoffice/libreoffice. Excel should not have a problem but recursion is used.

Categories: Lunar, Modelling