Monday, January 30, 2012

Reykjavik and GHCN adjustments.

There was a WUWT guest post recently by Paul Homewood on GHCN and GISS adjustments, and their effect on Iceland. It was somewhat along the lines of an earlier Eschenbach post on Darwin.

Then there were the usual thoughtful WUWT responses
When are the legal people going to be brought into this?
Someone should go to jail if this is tampering as it appears.
we’ve still a bunch of scumbags on this earth pretending that a dynamic history is OK
etc. So what happened

No, history was not rewritten. What the folks there don't seem to want to acknowledge is that GHCN circulates two files, described here. The file everyone there wants to focus on is the adjusted file (QCA). This, as explained, has been homogenized. This is a preparatory step for its use in compiling a global index. It tries to put all stations on the same basis, and also adjust them, if necessary, to be representative of the region. It is not an attempt to modify the historical record.

That record is contained on the other data file distributed - the unadjusted QCU file. This contains records as they were reported initially. It is generally free of any climatological adjustments. For the last 15 or so years, Met stations have submitted monthly CLIMAT forms. You can inspect these online. Data goes straight from these to the QCU file, and will not change unless the Met organisation submits an amended CLIMAT file. This is the history, and no-one is tampering with it.

The adjusted file does change, as the name suggests it may. Recently, it has been modified to use an improved pairwise comparison homogenization algorithm due to Menne and Williams. It is now (as of Dec 15 2011) used by GISS instead of their own homogenization algorithm, which makes the QCA file much more significant.

Update. I have a new post which looks at the GHCN adjustments more generally, with visualization.

Sunday, January 22, 2012

December 2011 temp, small changes for NOAA, GISS


TempLS showed a very small rise in global mean anomaly in December, from 0.358 °C to 0.364 °C. Now NOAA and GISS are out. NOAA has a slightly larger rise, from  0.437°C to 0.457°C. And GISS has a small fall, from 0.48°C to 0.45°C. All these are relative to their respective base periods. Time series graphs are shown here

As usual, I compare the previously posted TempLS distribution to the GISS plot. Here is GISS:

Lapse rates and entropy.

The dry adiabatic lapse rate (DALR) is in the news again. Willis Eschenbach has led a discussion primarily directed at a theoretical musing on whether gas under gravity but without heat input would have a lapse rate or be isothermal.

I've explained my views on the role of the DALR here and here, and in comments on several other blogs. Just a brief recap of theory; the DALR is the vertical temperature gradient given by:
dT/dz = -g/cp = -9.8 °C/km for air,
where z is altitude, g gravity acceleration, and cp is the (constant pressure) specific heat of air. Any gas cools when it expands adiabatically (ie without exchanging heat with the environment). The rate at which dry air cools as it rises (and the pressure falls) is also the DALR.

The air generally does have a lapse rate which is not quite as large as the DALR. This observed rate is called the environmental lapse rate. The difference is often attributed to the effect of water condensation, and there is reference to a moist adiabatic lapse rate. I think that is only part of the story, as I'll show.

But my view of the role of the DALR, and the answer to Willis' query, is fairly simple. Air motions create a heat pump which move temperatures toward the DALR. If you could prevent all motion, conduction would move the temperature gradient to isothermal. But you can't; in practice the air needs heating to keep it from liquefying, and that will always create motion.

In this post, I'll review the heat pump notions, and add an entropy viewpoint which will quantify some of the issues.

Friday, January 13, 2012

December TempLS surface temp - little change

A very small rise in global mean anomaly this month, from 0.358 °C to 0.364 °C.

Below is the spherical harmonic regional distribution. Some very high anomalies in Siberia and NW Canada.


Previous Months

November
October
September
August

More data and plots

Monday, January 9, 2012

Cherrypicker's guide to station trends

A while ago I posted a cherrypicker's guide to global surface temperature trends. This was partly in response to an outburst of the popular activity of selecting short periods where the trend could be seen as small or even negative. The idea was to embed this in a set of displayed results where you could get a broader picture of where such trends might be found, and how significant the regions were

Another popular activity is selecting stations which fail to show recent warming. So I've presented here a different kind of plot which shows all the GHCN stations on a world map, with shading to indicate the trend over the last 30, 45 or 60 years (you can choose). It derives from the plot I posted for November temperatures. It takes advantage of HTML 5 linear color shading, and uses a triangular mesh. Each station has a color corresponding to its trend for the chosen period; although the colors can vary locally, the station neighborhood itself should have the correct color. Note that there is no spatial averaging (except for the shading); the individual station trends determine the coloring.

One result that I found interesting is that while there are patchwork regions, eg USA, there are also large regions with fairly uniform trends, particularly the ocean.

So here's the plot. It is interactive - you can rearrange it, magnify, show the stations, click to see station detail and numbers etc. Use Ctrl+. Ctrl- to get it the right size for your screen. The mechanics are explained below.










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Click on this map to orient the world plot.




Show Stations
Show Mesh
Magnification


Trend period
Station





















































How it works

More details here. The flat map at top right is your navigator. If you click a point in that, the sphere will rotate so that point appears in the centre. The buttons below allow modification. Set what you want, and press refresh. You can show stations, and the mesh, and magnify 2×, 4×, or 8× (by setting both). You can click again to unset (and press refresh). Then you can click in the sphere. At the bottom on the right, the nearest station name and anomaly will appear. You may want to have stations displayed here. The selection menu chooses the period; if you change the period, the plot changes without need for refresh.

How the trends are calculated.

Calculating station trends is not trivial, because of missing values and seasonal variation. Obviously missing winter values at one end will bias the trend. A reasonable fix is to subtract the mean for each month and work with anomalies. But the means don't correspond exactly to the same period. I used a weighted least squares method similar to that used in TempLS. The weighting simply has unit value for months with readings, zero without. The model is xmy  ~  Lm  +  Tr  Jmy where x are the station readings, L the monthly offsets, Tr the trend, and J a linear progression of months, in century units. The suffixes m for month, y for year. This is fitted by least squares. The resulting formula is similar to OLS. If we now say that J has zero values for missing x, and I is a similar vector which is 1 mostly, but zero where x is missing, then the OLS trend formula would be
Tr = f(x) / f(J)  where   f(x) = S(Jx) - S(J) S(x) / S(I)
where S represents summation over all month/year. Denoting Sy as the process of summing over individual months, and Sm summing the resulting 12 sums, the formula from the above fit is:
Tr = f(x) / f(J); f(x) = S(Jx) - Sm( Sy(J) Sy(x) / Sy(I))

Data issues.

The data sets associated with these plots are getting larger, so attention to download time is needed. I'd like to be able to use gzip compression, but neither of the data stores I currently use support that. I have to send the data as text - basically Javascript assigns - so I use various tricks to get the text size down. I multiply by 100, say, to get rid of decimal points. I usually convert data to differences to make the numbers smaller. In fact, the biggest data item here is the world map. But potentially another big one is the triangle mesh, and there I had to make some compromises. I don't want to send a different mesh for each trend period, but if I send a mesh with all points, then in any one period, some stations will be missing. I dealt with this by using an interpolated value for coloring purposes. That's OK - the shading otherwise uses linear interpolation. But this isn't quite linear, and could look odd at times, though I haven't noticed anything. The missing (interpolated) stations don't appear when stations are shown, and are not reported when station values are produced by clicking. Anyway, the datafile size is now about 360 Kb, which is manageable. I'm looking out for better ways because I have ambitions that involve transmitting the whole TempLS dataset.

Notes


You may see a few ocean stations appearing on land. The reason is that I artificially create ststions at the centre of each 4x4 deg cell. If there is enough sea in the cell for HADSST to report a SST value, that will be assigned to that central point, even if it is on land.


Note that the color scheme suggests cooling, but most of the blue range is actually positive (though smaller) trend.


Stations are included in the trend analysis if they have at least 80% of months reporting within the range.