Wednesday, October 20, 2010

A ramble on GCMs Navier-Stokes equations.

This post is an outgrowth of a discussion at the Air Vent on GCM's and condensation. It's a kind of response to comment claims that GCN's don't allow for inversion, or volume change during condensation etc. I found myself saying often that it all comes out in the solution of the Navier-Stokes equations - you don't have to do something special.

It's often said that the N-S equations are at the heart of GCM's, but if you look at a set of equations actually solved, as in this set from CAM3, it isn't obvious. And it's made less obvious by the funny coordinates they use.

But it's true, and here I'll try to set out the reasons.

Thursday, October 14, 2010

Wahl & Ammann proxy calculations

I had been quietly plodding through Wahl and Ammann 2007. This is the paper that re-did the MBH98/99 proxy calculations using conventionally centred principal components analysis and a modified number of PC's. It's relevant to recent discussions of the Wegman report.

Some original code and data used in the paper is available at Nychka's site at NCAR. So I downloaded it. It's elegant in R. Just 11 lines of actual calculation to get from the proxy data to a set of proxy eigenvectors, with decentered scaling. And then, of course, R does the regular PCA for comparison in one line.

Then Ron Broberg put up a very helpful post drawing attention to a discussion by Dr Richard Smith of a recent paper by Li, Nychka and Ammann. As Ron says, it's well worth reading (as is Ron's post). I've only just started.

The R code

To get me going, I re-commented Ammann's code, to help my understanding. I'll show it, with the Figures, below the jump.

So the next stage is for me to recheck the things that are commonly said about the various proxies, and how they are reweighted. Later it might be possible to adapt the code for the Mann08 (Tiljander etc) analysis.

Wednesday, October 6, 2010

Can downwelling infrared warm the ocean?

Science of Doom has raised this question, which does crop up more frequently than it ought. Doug Hoyt, who should know better, has given it impetus.

It goes like this. Water is opaque to thermal IR, and not a good conductor. IR penetrates only a few microns. Therefore heat from incident IR from above must ...

be all converted to latent heat

or, be reflected, or ...

Land is also opaque to IR, but the idea that IR can't warm it doesn't seem to have the same attraction

Some thoughts below the jump.

Saturday, October 2, 2010

An entropy budget for the Earth

This post follows up some ideas in comments to the Science of Doom post on 2LoT. Whenever you calculate a heat flux, and you know the temperature, you can calculate the entropy changes. Tracking entropy is different from tracking energy flux, in that entropy is not conserved, but will be created whenever there is irreversible heat transfer. However, it is conserved in reversible processes, and can never decrease globally, although it can be transferred to somewhere else. And as with heat, for Earth steady state requires that entropy that enters or is created, must leave.

So I have the idea of doing an entropy budget, analogous to Trenberth's famous energy budget for the Earth. It's a bit more complicated though, so this post will look at a simplified Earth.