Monday, May 16, 2011

Wisconsin combined temperatures

Wisconsin has 23 USHCN stations, ranging from Ashland to Watertown, and I obtained the initial data on these (location etc) from the Surface stations site, before discovering that the USHCN server is back up. So, since there may be a possibility of it going down again and my losing some of the data I use, there is going to be another pause while I download the rest of the data that I need. That took longer than I thought, but now we can get back to Wisconsin.

Location of the USHCN stations in Wisconsin (USHCN )

There are three GISS stations on the list, in Milwaukee, Madison and Green Bay. And Milwaukee also appears in the USHCN. I had originally thought that it would be easy to decide which was the GISS selected station, given that it should be very close to the USHCN homogenized data, but when I compared the three sets of data they were slightly dissimilar.

Milwaukee Gen GISS temperature plot

Milwaukee Mount Mary College GISS station temperatures.

Because of the break in temperatures with the Mount Mary College, and also that it is closer to the USHCN location, I am going to assume that the GISS station that is used is the Gen one.

It was only after I made that decision and was re-aligning the data files when I ran a difference between the two stations, just out of curiosity. I took the Gen temperature from the Mt Mary College temperature, and got:

Difference between the Milwaukee Mt Mary College and the Milwaukee Gen data over time.

This has likely no meaning other than to show a possible measure of the scatter in the data from two relatively closely adjacent sites. And after having gone through this tortuous logic, it suddenly dawns on me that I have the co-ordinates of the Milwaukee station that is being used, and when I check it is the Gen one.

There were, similarly, a number of different stations available around Madison, so I chose the one that was closest to the location given for Madison on the citi-data page. It also, now that I have thought to look, agrees with the GISS station co-ordinates on the list.

Temperature change for Madison WI, GISS station.

And that only left Green Bay, which is also a station with data back into the 1880’s.

Temperatures for Green Bay Wisconsin GISS station.

So now we have the data, after having added the populations of the different communities, and we can go through the conventional analysis.

Difference between the GISS station mean and that of the USHCN stations in Wisconsin

This trends the other way from the usual one, but that may be because, as we will see later, there is a stronger "homogenization" of the USHCN data for this state than is also usual. Over the 115 years, the temperature of the state has increased at the rate of 0.6 deg F per century. (The homogenized data suggests a rate of 1.6 degrees/century).

Looking at the effects of geography, Wisconsin is 310 miles long and 260 miles wide, running from 86.82 deg W to 92.9 deg W and from 42.5 deg N to sensibly 47 deg N. The central latitude is at 44.43 deg N. The center of the USHCN stations is at 44.1 deg, while the GISS stations center around 43.5 deg N. The elevation of the state goes from 177 m to 595 m, with a mean elevation of 320 m. The USHCN mean is 265.8 m, while the GISS station mean is at 221 m. The impact that these values have on the true mean temperatures of the state may be seen when one considers the effects of geography.

First that of latitude, using the TOBS data since the USHCN homogenization tends to weaken the correlation coefficients for most of these relationships.

For longitude, though I may soon stop including this since the correlation is a dependant one, we get:

There is the expected stronger correlation with elevation.

And since I decided to use the 5-year latest temperature average to correlate with population, we get:

And then there is, of course the result when we subtract the original raw data (time of observation corrected) from the “homogenized” data prepared by the USHCN.


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