Saturday, August 28, 2010

California temperatures, the TOBS data

Back in April I first commented on the historic California temperature changes, using the homogenized data then available from the USHCN. Since then they have posted both the raw data and that corrected for Time of Observation (TOBS), as well as the data that has been adjusted to apply other perceived corrections. At the moment I am going back and seeing how the TOBS data is changed by those corrections. So this will examine that data, using the same form as originally. (Note that following the comment by Kinuachdrach the evaluation of Death Valley at the bottom of the piece has been UPDATED).

So first I go to the US Historical Climatology Network and download the 54 station set of data (there will be a short pause while I do this). And then there are the four GISS stations whose data we got the first time around (we aren’t going into those adjustments at this time). Looking at the difference between the few GISS stations and the average for the USHCN set it is interesting to note that while the GISS stations got successively warmer than the state average, in the raw data the reverse was the case, although the decline was very small.

The average difference between the two sets is 1.63 deg, which is the same as for the homogenized data. For the state as a whole, over the past 115 years there has been a steady warming trend, though the raw data suggests an average increase of 2 deg F per century, while the homogenized data suggests only 1.3 deg.

Looking at the effects of geography, there is the correlation with latitude:

There is virtually no change in the relationship of temperature with latitude, though there is sensibly no correlation with longitude, similar to the result with the homogenized data.

Given that California goes all the way to the sea, the effects of elevation should be significant, and in both cases they are.

The regression is a little higher than with the homogenized data (r^2 0.4) but otherwise they are much the same. Which speaks for having a significant number of stations in the state, since there were a significant number of years where there were dropped data from several of the stations. This becomes obvious as the standard deviation shows that scatter getting worse as the collective number of stations reporting peaked. Interesting with the raw data it is leveling off, whereas it was getting worse when the data was homogenized.

And even having to make some assumptions about the number of inhabitants of some of the more remote stations there is still a logarithmic correlation with population.

The correlation is slightly worse however (it was 0.10).

And just for grins, this is what has been happening in Death Valley, and it looks as though that has been getting hotter too.

California was the first state that I have looked at that was on the coast, and so it will be interesting to see if there is a coastal effect and define what it is, and how far inland it stretches. But for that we need more data.

Kinuachdrach made a comment on the Death Valley data (see below) and so I went to see what the condition of the weather station was, and discovered something that I thought readers might find of as much interest as I did. The full story is at the reference by John Daly.

There are, actually, two weather stations now in Death Valley, where the all-time highest temperature in the United States was recorded on July 10th, 1913, at 57 degC. Using the GISS data for California, the plot that is given is this:

And the site has a plaque that says:
"During the summer of 1998 - the warmest year on record - we recorded the hottest air temperature anywhere in the world of 53.06°C ±0.1°C (128°F) on 17 July 1998 at 3:15 pm local standard time."
Since the GISS plot stops before that, I am, being curious, just going to go to the GISS Site and download the latest version of the graph:

Note that since the high temperatures were single days, and the data plotted is the average for the year the records aren't evident. However the station was apparently changed in the 1990's to give the record at Badwater, rather than the earlier data that was recorded at Furnace Creek, according to John Daly. The differences are, among others, that Badwater (as documented) is more of a sun trap than the old station, 20 miles away out in the open, at Furnace Creek.

But it is worth commenting that over at Watts Up With That, Steve Goddard has noted that there seems to be some work on re-adjusting the data back to 1998 that removes the overall high temperature that they showed then (and which agreed with other records) in favor of lowering that temperature so that the overall graph now shows a steady increase in temperature over the last three decades (which does not agree with other records). So when I show you the GISS record (which as with the USHCN data is modified from the original raw data) until I have worked out (or more likely someone else has) what was done with that data before it was plotted, all I can give you is what is on the record. And in this case, I suspect it is only a part of a continuing story.


  1. That Death Valley temperature record is very interesting. The area has always been hot, low population.

    The temperatures show a lot of variability from about 1910-1960; stable from about 1960-1985; stable at a slightly higher temperature 1985-2000; slighlty higher again in the last few years.

    It would be very interesting to compare that with the maintenance and calibration records of the temperature station. For obvious reasons.

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