somewhere I have a study or two on the issue of sampling interval. there is also jerry bs data
and crn data.

That’s one of the points I was trying to get across Sam. We seem to get a max and min, and thereby a mean, but no median, and as far as I can tell no indication as to what time the max and min occurred at. These things would seem to be of particular interest, but if we can’t even run a collection of temp monitoring stations correctly now, as per Anthony Watts work, and we can’t be guaranteed of the accuracy and location of stations over a history of decades, chances of getting that info is pretty slim. We could start trying to collect such things now, but have no way without the usual hand waving that goes on to connect that with past measurements.

Off the cuff, when the max and min occur and how long it stays low or high, during a day, would seem to offer significant information that might help identify why the temps were what they are, UHI, weather, global warming, etc.

Jerry B had linked to about 6 years worth of airport station data (warning: lots of data!) that had actual temperature recorded hourly. From that, you can reconstruct the Tmax and Tmin data that would be recorded by time of day and estimate those biases. USHCN has an adjustment for time of observation bias, and from what I’ve seen, the science behind it is sound. However, I am unconvinced that the execution of the adjustment regime appropriately accounts for the bias. I’ve been working on this in my spare time for a couple of months.

There was an entire thread about TOBS last year. I will say this, time of observation bias is complex. It varies by latitude, season (i.e. proximity to soltices and equinoxes), local conditions (Minneapolis is very different than Seattle), and there are year-to-year variations.

Correcting for it is even more complex, because you not only need to know all of the things above, you also need a reliable historical record of the time of observation for each station. That might be the most difficult part of all.

Hope this helps.

The dark surface looks like soil that has been oiled to keep down the dust. Since the station is directly on top of this artificial heat-generating surface, I think the station would be an easy 5 on either the CRN or Meteo France scales, not a 4 as rated by Anthony.

What level of adjustment is incorporated into the graph?

Agreed Reno is a very important example because it demonstrates vividly a number of points. I admit to personal confusion between the various homogenised versions because I do not track them as closely as you do.

You mention sharpening data collection in other countries. The Aust quality network now touted has about 100 stations selected from 1,200 or so on the basis of length of record, rural status, etc. This was improved by a “homogeneity assessment using a number of objective and semi-objective techniques..” whatever they are. Cut to the chase, the main stations are now typically at airports at small towns inland, it at remote coastal places, typically lighthouses. I am uneasy with this, because if a fatal flaw is found with either class of station, much of the coverage will disappear either from inland or from the coast.

Ref with stats description is Aust. Met. Magazine 53:2 June 2004, Paul Della-Marta et al. Some interesting comments on corrections using distant stations. Main conclusion to 2002 is 100 years of increase, mainly in min temp of about 0.6 deg.C.

Lastly, a quick comment on average daily versus mean daily temp. I’d sooner average, because for some types of instrument a transient effect will give a false max or min of greater moment than the average. But we don’t have much more to use than max and min in most places up to 20 years ago. I don’t know if we now have thermocouple errors here when changing from Hg in glass.

My apologies to all for comparing a min temp graph to a mean temp graph. I slipped up. Geoff.

p.s. What is more, I admitted it.

Change in location of [Reno] weather observing sites:

The climate record for Reno, Nevada extends back to 1870, but the official observation site has moved occasionally during that period. By referring to U. S. Weather Bureau / National Weather Service (NWS) Local Climatological Data (LCD) Annual Summaries for Reno, a chronology of weather observation station moves can be derived.

From December 1, 1870 until December 31, 1887 daily rainfall data was collected by the Southern Pacific Railroad Company agent at the rail depot in Reno. Starting on January 1, 1888 and continuing through November 10, 1905, maximum and minimum temperature data, and precipitation data, were recorded at the Administration Building (Morrill Hall) on the University of Nevada campus north of town.

The U.S. Weather Bureau took over official observations for Reno on November 11, 1905. The Weather Bureau’s first observation site was at the Thoma-Biglow Building, on the northwest corner of First and Virginia Streets, and continued here until February 28, 1910. Starting on March 1, 1910 and continuing through February 28, 1934 weather observations were taken at the I. O. O. F. (Independent Order of Odd Fellows) Building on the southeast corner of Second and North Center Streets. The final downtown location was at the Post Office Building on the northeast corner of South Virginia and Mill Streets. Weather observations were taken here from March 1, 1934 through August 31, 1942.

In order to assist the growing aviation industry, weather observing stations were opened at airports along the nation’s transcontinental air routes (Whitnah, 1961). The Weather Bureau’s station at Reno’s airport (then called Hubbard Field) opened on January 8, 1931. Twenty-four-hour duty, along with hourly weather observations and upper air observations, started at this time. However, weather observations were now being taken at two locations concurrently (Hubbard Field and the downtown Post Office). This situation continued from January 8, 1931 through August 31, 1942 (when the city Weather Bureau office at the Post Office Building was closed). On September 1, 1942 the airport became the official observation site for Reno. This airport continues to be the official weather observation site to this day.

The transfer in official observation site to the airport constituted a change to a location a few miles outside of town (actually 3.5 miles south southeast of the Post Office). However, the airport was “farther away”, so to speak, then than it is now. In the 1930s and early 1940s this area was rural. The city of Reno has expanded in area over time and the Reno-Tahoe International Airport is now surrounded by an urban area. This difference between the two locations can be seen with precipitation, and especially temperature, data for Reno. There was a continual rise in average annual temperatures from the late 19th century through the 1930s (a gradual evolution from wood structures to brick and stone buildings and paved roads in town?). During the 1940s the average temperature was conspicuously less than it had been (since the readings were now being taken in a rural area). Average temperatures then started a gradual warm-up, with impressive rises during the 1980s and 1990s (urban heat island effects). In a strongly developed heat island, the temperature in the urban area can be up to 10°F greater than it is in the surrounding rural areas (Oliver and Hidore, 2002). Emphasis added.