How polar ice is modulated by the sun
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.
I can model that very closely using a single function plus a fixed offset, which is unimportant.
Now here is one overlaying the other.
The match is r2=0.96
Here is the remainder, subtract the model from the data
Now lets switch to showing you the details.
The function is trivially simple, a pure sine wave with a period of 2 years which has been made single polarity.
Here are the spectra
Why does the ice amount follow that exact law?
The data from the SORCE satellite which measures TSI also includes data for 1AU distance i.e. earth/sun distance and this primarily shows the variation in solar irradiation during earth orbit.
Look carefully, minimum ice occurs when solar irradiation is highest and the converse. Perhaps the surprise is the almost exact sine/cosine shape but that is a pure rotating vector… and so is a near circular planet orbit, ours.
My critical point here is the creation of a unipolar signal from a bipolar stimulation. This is a non-linearity and creates an otherwise unexpected harmonic structure. I point out that the sunspot cycle is something similar, can only but appearing sunspots, never negative spots! (the solar magnetics tell a different story and why there is an underlying slower magnetic cycle)
In fact the earth has an inclined axis, not quite the same thing as the TSI variation, but the SORCE data is a very accurate measurement. (the shown curve is from a model derived from 3 hourly data)
You will notice the phase of the ice variation and the phase of TSI differ slightly. The exact projection used by the the sea ice data providers influences this, JAXA/IJIS is slightly different. (same result, yes)
The same effect does not occur for the Antarctic which is land surrounded by sea ice instead of sea ice surrounded by land as it is for the Arctic.
From a palaeoclimatology point of view the elliptical earth orbit is not contant.
This like says a little about this with more detail than usual in general texts
I will leave it at that for the moment.
NOAA and SORCE are both very well known datasets, I give no links.