Observing temperatures in the late afternoon results in temperatures about 0.45 C warmer on average than if temperatures were observed at midnight. The ASOS and I think the Nimbus sites that have hourly and the new CRN has hourly. When the thermometer is read, which time periods might contribute to today’s reading? And, by definition, one incorrect outcome would be to allow a moment to exist in two different time periods. is less than 3.49 Sigma of the mean is also 2 in 10000. Correct? The reconstructors are trying to develop an “accurate” temperature record vs just finding the rate of change. Overall avg = 18.3. noon 0.04 -0.07 0.36 0.24 0.05 0.25 0.57 0.55 0.25 0.50 0.21 0.16 0.30 0.15 13.86 13.82 rather than -5C. Yes, because that was the high for the 24 hour period ending at 6 PM on day 2. The method of slopes would eliminate a lot of confusion. [M2006e,T2006e] is the data pair associated with the Moment at the end of 2006, and Temp at end of 2006, [M2007b,T2007b] is the data pair associated with the Moment at the start of 2007, and Temp at start of 2007, The moment at the end of the first time period, M2006e TOBS = Temperature at the time of observation (tenths of degrees C) Divide your results by 10, multiply by 9/5 + 32 to convert to F (or whatever you need to do). The difference between the MrPete and JerryB algorithms for determining high/low/average helps explain how TOB becomes a problem. hour periods ending at 36167 hypothetical 24 hour periods of observation: 3 instances of 14 occurrences Did afternoon TOBS cause double counting of hot days in 1936? Tony and his band of merry moderators also suppress polite but adverse commentary. Which information tells me basically nothing because there’s a whole bunch of combinations of the 1440 values that would give me the same average. TOBS 1: 20 RE 70. What if the weather stations were manned by experienced people who liked their craft and were not stupid. The fact of the underlying discrete measurement grid has significant implications on correct management of calculations. No. one must include the 24 hour old measurements. Rats! No one has demonstrated any issue in actual data with TOBS adjustments that has anything It looks to me like when temp at time of observation is lower than the min temp, they select the temp that looks more in line with surrounding days. IF you start collecting temps at Midnight and then SHIFT to 7AM you will induce a shift in both Because those branches allow you to Anthony, I think I have a proposal for the pre 1900 records. Then. Otherwise, we’re dealing with “analysis” via interpolation or extrapolation, right on the data entry forms. C, which would justify an upward adjustment of +0.25 deg. Jan 1 hi/lo/avg = 10/10/10 If the temperatures rose, the index would remain where it was as the fluid flowed past it. This anomaly will appear on the record for the 24-hour period ending at the TOB and the 24-hour period beginning at the TOB. As Steven M says they are not looking for temperatures they are looking for the trend. What we should be seeing is a steady reduction in TOB to zero, rather than the steady increase we do see. change was made. As a result, by assuming 7 AM observation for all AM stations and 5 PM for all PM stations, a good estimate of the median bias is obtained for all AM or PM observations. But we don’t know that and cannot guess. I just read Karl, Williams, Young, and Wendland (J. For example, if yesterday’s AT OBSN temperature was 95, today’s maximum must be at least as high as 95, even if the maximum this calendar day was only 86. Jerry One thing I was thinking of doing was a simple Graph. 2:00 51.67 min(or max) temperature in 24 hour periods ending at 36167 hypothetical (It wouldn’t shatter the glass because unlike water, mercury contracts when it freezes). And I don’t just mean in climate science. According to Karl et al, before WWII most stations used to measure in the evening, with 5pm being the most popular time, but an increasing number are moving to the morning, with 7am being the most popular time. And any measurement at that moment is part of 2007, not part of 2006. How do you correct the TOB adjustments to account for variations between solar time-of-day and wall time-of-day? 16:00 52.61 10:00 51.26 This bias of 0.5 C is of similar magnitude in the minimum, maximum, and mean temperatures. But what about hot days? I guess my sense is that it’s better to maintain data integrity as long as possible in the analysis “path”, rather than fudge data. See other definitions of TOBS One thought experiment: imagine a sine wave, sampled at regular intervals. first step of my method. The huge USHCN TOBS adjustment shown by John V (#376) is therefore highly suspect. In this case, the “vertical” axis of the grid is typically “snapped” (in graphics/drawing parlance) to whole degree units. It should be remembered,however, that missing data reduces the effective sample size. One cannot simply remove the grid and presume to obtain correct results in infinite precision real number space. I quickly tossed one idea because it seemed to leave too much missing data to be acceptable. The drawback, of course, is that you can only use stations with a long history of hourly (or three hourly) readings. Then took the 6.5 year average of the daily averages. Number of instances in which the current 24 hour min is at exactly the same – Some sensors are read using truncation (observers always report whole numbers! 1 for station locations relative to Mohonk Lake). Then there is the topic of response times. read the min/max at Midnight in one ( and reset) The method of estimation should work correctly anywhere, yes? The most interesting part of an interesting paper was how he worded something about the midnight ideal reading of daily observations. Do we really need to align the different stations to be recording the exact same 24 hour sequences? Yes, we can draw an imaginary continuous line between our measurements, but when we want to fix a given temp/time estimate along that curve, we recognize it will resolve to a spot on the grid, never in between grid points. The figure below shows the four major adjustments (including quality control) performed on USHCN data, and their respective effect on the resulting mean temperatures. Astute observers will be aware that weather stations don’t take a single temperature measurement at the observation time. Temperatures are consistently lower in the TOBS biased data after the shift in observation time for daily minimum, maximum, and mean temperatures. It is clear that the shift from afternoon to morning observations in the United States introduced a large cooling bias of about 0.3 C in raw U.S. temperatures. hour periods ending at 36167 hypothetical 24 hour periods of observation: 1 instance of 15 occurrences The challenge we’re working through is how to properly perform the analysis that underlies the topic of this thread: Time of Observation Bias… and in particular how to handle the specific situation where you have a series of hourly temperature values.