Thanks for directing me to the CA thread. I found a copy of Karl, et al, 1986 in Hu McCulloch’s comment #110:

http://ams.allenpress.com/archive/1520-0450/25/2/pdf/i1520-0450-25-2-145.pdf

I read the article hurriedly but I need to give it more thought. My first impression is that TOBS may introduce considerable distortion to the areal data. For example, the month-to-month variability for Mohonk Lake listed in my 10/19 message, especially in the 1956-2006 interval, doesn’t seem logical to me. This variability may be due to the spatial patterns of δ shown in Fig. 6 of the article. The gradients for δ are quite steep during DJF in the Mohonk Lake region. The iso-contours also shift quite rapidly.

I found nothing in the TOBS article that explains the significant step-wise changes in the difference between the areal and COBS data occurred in 1909 and 1955 for Mohonk Lake. I checked several monthly B91 Forms before and after 1909 and 1955 and there were no significant change in Time of Observation. (In 1954 and 1956, the time listed on the B91 forms was 4:00 PM; in 1908 and 1910, the time listed was either 6:00 PM or “about sunset.”)

In the Fort Collins example that I mentioned where there was no difference between the areal and TOBS data between 1905 and 1940 … I guess the TOBS “adjuster” must have been “OFF” during that interval!!

Needless to say, I am still puzzled by the inexplicable step-wise changes that I have observed. I’ll examine some more sites when I have time and see if a similar pattern persists.

BTW, I noticed that many of the comments on the CA thread referred to COBS as though it was used to adjust the daily TMAX and TMIN data. Since the B91 Forms list only the time of observation for the month, it seems clear to me that COBS is a monthly adjustment.

Thanks, also, for the guidance on how to export a graphic from Excel to WordPress. I’ll try using it to display some of the step-wise changes that have been puzzling me.

Is COBS a typo, and you meant TOBS?

I cannot explain the algorithm behind the TOBS adjustment, because I have not obtained a copy of Karl, et al. 1986; Vose et al., 2003 (see the links in the main body of this post). TOBS has been discussed at length on Climate Audit, particularly on this thread. You should be able to pick up some interesting insight from the comments (I myself need to reread it). In particular, one of the early comments points you to a pretty good description of TOBS here.

As for getting an Excel chart into WordPress. Here is a very simple procedure:

1. Click on the chart object, then press CTL-C to copy the chart (make sure you click on the chart near the edge, and not a location closer to the center, otherwise you end up with just the plot area or an axis.)
2. Open Microsoft Paint. An empty artboard will appear.
3. Press CTL-V to past the chart image into paint.
4. From Paint, click File>Save As and save as a GIF image into a directory of your choice.

Now, when you go into WordPress you can upload your GIF image and reference it.

I should have indicated that the first part of my message pertained to Mohonk Lake.

TOBS continues to be a mystery to me. I have compared the areal data with the COBS data in hcn_doe_mean_data file for the 1900:2006 interval and was perplexed by the results. Significant step-wise changes in the difference between the areal and COBS data occurred in 1909 and 1955. All difference values were constant between the changes as listed below:

MONTH 1900-08 1909-55 1956-2006
JAN 1.10°F 1.10°F 1.40°F
FEB 1.10°F 1.50°F 1.80°F
MAR 0.70°F 0.90°F 1.30°F
APR 0.60°F 1.10°F 1.50°F
MAY 0.50°F 1.30°F 1.60°F
JUN 0.30°F 0.88°F 1.20°F
JUL 0.30°F 0.80°F 1.00°F
AUG 0.50°F 1.00°F 1.20°F
SEP 0.70°F 1.31°F 1.60°F
OCT 0.80°F 1.11°F 1.50°F
NOV 1.30°F 1.31°F 1.70°F
DEC 0.90°F 0.90°F 0.90°F
AVE 0.72°F 1.10°F 1.41°F
DJF 1.00°F 1.18°F 1.43°F
MAM 0.58°F 1.09°F 1.47°F
JJA 0.37°F 0.90°F 1.13°F
SON 0.94°F 1.23°F 1.60°F

I also compared the areal data with the COBS data in hcn_doe_max_data and hcn_doe_min_data files for the 1900:2006 interval and observed the same step-wise pattern, although the values were different.

I have also made the same comparisons for other surface station and observed similar perplexing differences between areal and TOBS data. For example, Fort Collins, CO (053003) for the 1900:2006 interval displayed significant step-wise changes in TAVG, TMAX and TMIN in 1905 and 1940 but there was no difference between the areal and TOBS data between 1905 and 1940.

Can anyone explain to me how NCDC calculates TOBS?

REPLY: Yes and no, you can get the absolute RAW B91 data forms free, but you have to hand transcribe. If you want a CD of data, then yes you have to pay for it to NCDC. – Anthony

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I should have noted that under “…some of my observations:” the step-wise changes in Adj RAW TAVE, Adj RAW TMAX and Adj RAW TMIN were with respect to the average annual temperature.

Also, another correction:

3. Adj RAW TMED = Adj RAW TMAX – Adj HCN TMAX

should have read

3. Adj RAW TMED = [Adj RAW TMAX + Adj RAW TMIN]/2

Again, sorry about the confusion. I guess I was in too much of a hurry to go to dinner.

HCN del TAVE = HCN TAVE –HCN TAV3

should have read

HCN del TAVE = HCN TAVE –HCN MED

Sorry about that …

Thanks again for your insights. I have commented previously on this blog that I have been puzzled by what appeared to me to be step-wise adjustments that NCDC makes to surface station data. As I’m sure you know, WRDC archives surface station data which I compared to USHCN data for several surface stations and observed the step-wise differences. I wondered if the similar step-wise differences might be observed between NCDC’s daily and monthly data sets for Mohonk Lake,NY (305426). I have completed my analysis and observed similar step-wise differences between the daily and monthly data sets.

I use Excel but, unfortunately, I haven’t learned how to export Excel graphics to WordPress. It would be much easier to convey what I have observed if I could do so. If you permit me, I’ll try to briefly explain what I have observed.

First, I refer to the HCN data set as the RAW data set. I updated the RAW data set by correcting the -77°F transcription error and using the B91 Forms to fill the data cells for the missing six days. While doing that, I realized that the entire B91 Form for April 1965 had not been transcribed properly. Therefore, I incorporated the B91 Form data.

I then calculated the monthly averages for TAVE(F), TMAX(F) and TMIN(F), for the interval 05/1948 through 12/2005 and compared the results with the corresponding monthly values that I downloaded from
http://cdiac.ornl.gov/cgi-bin/broker?_PROGRAM=prog.climsite_monthly.sas&_SERVICE=default&id=305426

I defined the following adjustments:

1. Adj RAW TMAX = RAW TMAX – HCN TMAX
2. Adj RAW TMIN = RAW TMIN – HCN TMIN
3. Adj RAW TMED = Adj RAW TMAX – Adj HCN TMAX
4. Adj RAW TAVE = Adj RAW TMED + RAW del TAVE – HCN del TAVE

Where

1. RAW del TAVE = RAW TAVE – RAW TMED
2. HCN del TAVE = HCN TAVE –HCN TAV3

Briefly, here are some of my observations:

1. Stepwise adjustments occurred in 1954-56 and in 1990.
2. Steps-wise changes in Adj RAW TAVE:

Average 1949:1954 = 0.39°F
Average 1956:1980 = 0.63°F
Average 1991:2005 = 0.03°F

3. Steps-wise changes in Adj RAW TMAX:

Average 1949:1954 = 1.27°F
Average 1956:1980 = 1.85°F
Average 1991:2005 = 1.20°F

4. Steps-wise changes in Adj RAW TMIN:

Average 1949:1954 = 0.92°F
Average 1956:1980 = 1.02°F
Average 1991:2005 = 1.62°F

So … does this make any difference from a climate change perspective? I don’t know. For the 1949:2005 interval, simple linear regression shows the following:

RAW TAVE = 1.79°F
HCN TAVE = 1.55°F
RAW TMAX = 2.56°F
HCN TMAX = 2.97°F
RAW TMIN = 1.01°F
HCN TMIN = 0.19°F

I guess that it depends upon on your perspective.

The second sentence in the last paragraph should have read: “It turns out that the value of 77°F recorded on the B91 Form for second day of that month…”