Tuesday, July 7, 2015

Maintained WebGL map of past GHCN/SST station anomaliess

I have a maintained page here which shows anomalies for individual land stations and SST cells, averaged over each month. Land data comes from GHCN V3 unadjusted, and SST from ERSST, formerly ver 3b. It is a shaded color map, with true color for each station, and linear interpolated color in between. I think it's the best way of seeing the raw data.

Now that I am doing daily runs of TempLS mesh, and this produces much of the necessary data, I have decided to make production of these maps a subsidiary process. This saves duplication, and keeps up to date with versions (using now ERSST 4). But what may be more useful is the daily updating. That means that the latest month can be tracked progressively as data comes in. So today, I am waiting on data from Canada and some Latin American countries before posting the TempLS result for June. But you can see it here, and it shows how TempLS calculates its interim result with interpolation. Of course, you could wait till tomorrow when Canada will probably be in.

I have also extended the range back to 1900. You can examine any month in detail. I haven't yet done the annual and decade averages back beyond 1990, but soon.





Friday, July 3, 2015

NCEP/NCAR in June

Data for the Moyhu NCEP/NCAR index is now in. It was a month of contrasts - starting very warm, then cold, and ending somewhat warmer. The end result of 0.204°C (1994-2013 base) puts it similar to January. You can now see the map of average temperatures for the month. Warm in west N America and NE Pacific (strong El Nino pattern), also in W Europe and W/central Russia. Extremes in Antarctica, mostly cold. Cool in E Mediterranean.

As noted here, there is predictable month-month variation associated with choice of anomaly base period. That was partly responsible for the discrepancy between a May rise in the index, and a flat GISS. To try to counter this variation, I have added a section of the table below the monthly indices which tries to put the index on the same anomaly base as GISS or NOAA. It can't do this directly (lacks good data), but can work out that component of the change based on other indices during 1994-2013. IOW, it's the corrected prior estimate for those indices. That estimate is that GISS should be about the same as May (0.72°C), while NOAA should be about the same as April. However, NOAA has been consistently exceeding expectations lately.

Update. Troposphere data: RSS is up from 0.31 to 0.391°C; UAH v6 is up from 0.27 to 0.31.

Thursday, July 2, 2015

TempLS V3 - part 3 - results

This is third in a series (part 1, part 2), about TempLS ver 3. The first part gathered a big array x of temperatures of land and sea. The second made an array w (with similar form) of weights, and a combined station inventory iv. As explained here, that is all you need for a simple iterative process to compute temperature anomalies and their average by a least squares process. The code to do that will be described here.

Monday, June 29, 2015

NCEP/NCAR monthly average maps.

A short time ago, while writing about the discrepancy between the NCEP/NCAR index and TempLS mesh, I made a temporary modification to the daily WebGL plot to show monthly averages. I've now formalised this. There is a black bar at the top of the date selector, and if you mouseover that, it will offer monthly averages. They are all there now, including the current month (to date). I expect this will be kept up to date.

Friday, June 26, 2015

TempLS V3 - part 2

In my previous post, I began a three part description of the new vwrsion of TempLS. That part was devoted to the collection of land and SST data into a temperature data array.

The next part is about forming the other basic array for the calculation - the weighting array, with one entry for each temperature measurement. I've described in various posts (best summarized here) the principles involved. A spatial average (for a period if time, usually month) requires numerical spatial integration. The surface is divided into areas where the temperature anomaly can be estimated from data. If the subdivisions do not cover the whole area, the rest will be assumed (by the arithmetic) to have the average anomaly of the set that does have data. The integral is formed by adding the products of the estimates and their areas. That makes a weighted sum of the data.

Traditionally, this was done with a lat/lon grid, often 5°×5°. An average is formed for each cell with data, in each month, and the averages are summed weighted by the cell area, which is proportional to the cosine of latitude. That is not usually presented as an overall weighted average, but it is. HADCRUT and NOAA use that approach. TempLS originally did that, so that the weight for each station was the cell area divided by the number of stations reporting that month in that cell. Effectively, the stations are allocated a share of the area in the cell.

Of course, this leaves some cells with no data. Cowtan and Way explored methods of interpolating these areas (discussed here). It makes a difference, because, as said, if nothing is done, those areas will be assigned the global average behaviour, from which they may in fact deviate.

Recently, I have been using in preference an irregular triangular mesh (as shown right), of which the stations are the nodes. The weighting is made by assigning to each station a third of the area of each triangle that they are part of (see here). This has complete area coverage. I have continued to publish results from both the grid and mesh weighting.

The code below shows how to form both kinds of weights. Note that the weighting does not use the actual measurements, only their existence. Stations with no result in a month get zero weight. There is no need for the weights to add to 1, because any weighted sum is always divided by a normalising sum.

Wednesday, June 24, 2015

TempLS: new V3

TempLS is my R program that I use for calculating global average temperatures. A recent review of the project is here. A few weeks ago I posted an iterative calculation sequence which is the basis of the program. I noted that the preliminaries for this were simple and mechanical. It requires the data just organised in a large array, and a set of weights, derived from station locations.

I've never actually released version 2.2 of TempLS, which is what I have been using. I did a documented release of v2.1 here. Meanwhile, the program continued to accumulate options, and got entwined with my automatic data acquisition system. So I thought it would be useful to create a simplified version with the basic functionality. I did post a simplified version once before, but that was land only, and with more primitive weighting.

So I'm planning to post a description with three parts. The first will be data gathering, the second weighting, and third is the calculation, which has already been covered. But there may be results to discuss. This is the first, which is about the data gathering. There is no fancy maths, and it is pretty boring, but useful for those who may use it.

Sunday, June 21, 2015

TempLS and the new ERSST V4

NOAA is now using their new V4 ERSST, and so should I. It has come along at a time where I am preparing my own V3 of TempLS (more below), so I will make a double transition.

But first I should mention an error in my earlier processing of V3b, noted in comments here. ERSST3b came in decade files; that helped, because decades before the present did not change and did not require downloading. So I collected them into a structure, and with each update to the current decade (every month) merged that with the earlier decades.

However, I misaligned them. Most climate data uses the strict decade numbering (1961-90 etc), but ERSST uses 2000-2009. I got this wrong in the earlier data, creating a displacement by 1 year. Fixing this naturally gave better alignment with other datasets.

I'll describe the new TempLS version in detail in coming days. V 2.2 of TempLS had become unwieldy due to accumulation of options and special provisions for circumstances that arose along the way. I have made a new version with simplified controls, and using a simple iterative process described here. It should in principle give exactly the same answers; however I have also slightly modified the way in which I express ERSST as stations.

The new version is an R program of just over 200 lines. Of course, when simplifying there are some things that I miss, and one is the ability to make spherical harmonics plots (coming). So for a while the current reports will lag behind the results tabled above. That table, and the various graphs on the latest temperature page, will now be using ERSST v4.

Below the fold, I'll show just a few comparison results.