In the discussion of the Tucson weather station, Ben Herman of the U of Arizona observed that there were serious biases with the HO-83 hygrothermometer – introduced in the early 1990s – which was said to be a contributor to the uptick to Tucson values. Although USHCN has implemented adjustments to U.S. data to deal with time-of-observation bias and station history, both of which resulted in significant upward adjustments of recent data relative to earlier data, I have been unable to see any evidence that either NOAA or NASA made any attempt to adjust for the upward bias of recent readings using the HO-83 thermometer, although its problems are thoroughly discussed in the specialist literature.
Problems with a warm bias in the HO-83 system were first reported in print in Gall et al 1992 in connection with Tucson here. Kessler et al 1993, a follow-up article about stations in New York by some of the same authors said:
They indicated that the HO-83 maximum temperature readings at Tucson were probably too warm by 1-2 deg C on sunny, light wind days, that the problem could probably be attributed to the design of the instrument and that an investigation was under way… Their investigation (Gall et al 1992) revealed that the warm bias (~1 -2 deg C) maximized shortly after solar noon and that the bias was very small or even slightly negative shortly before sunrise. Consequently recalibration checks done in the early morning would fail to reveal any bias in the HO-83 hygrothermometer.
Cyrus G. Jones and Kenneth C. Young 1995 said :
Examination of differences between the two instruments found that the original version of the HO-83 read approximately 0.6 deg C warmer than the redesigned instrument. Significant changes in the differences between the two instruments were noted between winter and summer. It is suggested that for stations with climatology similar to the ones used in this study monthly mean temperatures reported by the original version of the HO-83 be adjusted by adding -0.4 deg C to June, July August and Sept observations and by adding -0.7 deg C for the remainder of the year.
These results were noted up in Karl et al 1995, which was discussed in Karl and Knight 1996 as follows:
Karl et al. (1995) show that, on average, the HO-83 increased the maximum temperature by about 0.5°C relative to the HO-63 instrument and also increased the minimum but only by 0.1°C. Much larger effects have been noted in Tucson, for example (Gall et al. 1992), and Jones and Young (1995) also find a consistent positive bias at several stations they examined in the southern and central plains. This suggests that the trends of maximum T in Chicago are biased warm not only due to increased urbanization but by the introduction of the HO-83 instrument in 1986.
Gaffen and Ross 1999 cite these results as follows:
Karl et al. (1995) suggest that the change to the HO-83 hygrothermometers in the 1980s may have lead to spurious increases of 0.5 C in daily maximum temperature and maybe 0.1 C in daily minimum temperature, but that the exact bias of any one instrument is unknown.
Karl et al 2002 discusses the adjustments even showing the figure below:
Karl et al 2002 Figure 2.
The problem is discussed again in Lin et al (2003) which said:
The HO-83 maximum temperature readings were about +1 to +3 C higher on sunny, light wind days. The research of both Kessler et al. (1993) and Gall et al. (1992) illustrates the need to account for shield/sensor bias prior to analysis of operational NWS temperature data and determination of short-term temperature trends. Other researchers (Robinson 1990; Canfield and McNitt 1991; Meyer and Hubbard 1992; Croft and Robinson 1993; Blackburn 1993; Easterling et al. 1993; Guttman and Baker 1996; Andresen and Numberger 1997), in various ways, pointed out the climate data discontinuities and trends or changes in variability resulting from changes of temperature measuring systems and site locations.
It is also discussed at length in Peterson 2003 (which has been discussed previously at CA) : Peterson actually carries out an adjustment for HO-83 (an adjustment not evidenced in USHCN as discussed below). Peterson 2003 said:
However, C. Jones (2000, personal communication) reprocessed the data with extreme daily maximum and minimum hourly temperatures as surrogates for maximum and minimum temperature. The mean temperature adjustment is the average of the maximum and minimum since mean temperature in the U.S. cooperative network is the average of the maximum and minimum daily temperature. The annual mean temperature adjustment that results from this methodology, +0.6 deg C, is in keeping with the approximately 0.6 deg C warmer value determined by Jones and Young (1995). This value is added to the data from the HO-83 to make them comparable to the ASOS instrument. This adjustment to the ASOS standard essentially removes the HO-83 bias
Peterson 2003 also discussed Comrie 2000 (discussed previously in connection with problems in Tucson) in a disapproving way, stating that part of the urban bias reported in Comrie 2000 may be due to HO-83 problems not discussed by Comrie:
Comrie (2000) did not reference Gall et al. (1992), which looked at then-current measurements at the National Weather Service Office in Tucson and found daytime temperatures that are two to three degrees too high.
So problems with the HO-83 thermometer are amply documented in specialist literature. USHCN has been quick to adjust time-of-observation bias which worked in the direction of increasing 20th century trends – what have they done to adjust for HO=83 bias which caused an upward bias to measurements in the 1990s?
USHCN version 1 adjustments are summarized here and include no HO-83 adjustment although they purport to adjust for introduction of MMTS as well as the TOBS and station history adjustments discussed elsewhere. Likewise USHCN Version 2 do not adjust for HO-83 bias.
I must confess that this indicates at least the possibility of a bias in adjustment decisions: one is hard-pressed not to take away an impression that, if the HO-83 adjustment had increased 20th century trends, that Karl and Hansen would have been on it like a dog on a bone, but, since the adjustment will lower late 20th century temperatures, the adjustment mysteriously becomes too elusive to implement. Just an impression.
Gall, R, K. Young, R. Schotland, and J. Schmitz , 1992. The Recent Maximum Temperature Anomalies in Tueson: Are They Real or an Instrumental Problem? Journal of Climate Volume 5, Issue 6 (June 1992) pp. 657665 url
X. Lin, K. G. Hubbard, E. A. Walter-Shea, J. R. Brandle, and G. E. Meyer, Some Perspectives on Recent In Situ Air Temperature Observations: Modeling the Microclimate inside the Radiation Shields, Journal of Atmospheric and Oceanic Technology, pp. 14701484 url
Cyrus G. Jones and Kenneth C. Young , An Investigation of Temperature Discontinuities Introduced by the Installation of the HO-83 Thermometer Journal of Climate Volume 8, Issue 5 (May 1995) pp. 1394140 url
Ronald W. Kessler, Lance F. Bosart, and Robert S. Gaza, Recent Maximum Temperature Anomalies at Albany, New York: Fact or Fiction, Bulletin of the American Meteorological Society, Volume 74, Issue 2 (February 1993) pp. 215226 url
Dian J. Gaffen and Rebecca J. Ross, 1999. Climatology and Trends of U.S. Surface Humidity and Temperature, Journal of Climate 12, 811-828. url
Karl, T.R., and Coauthors, 1995: Critical issues for long-term climate monitoring. Climate Change, 31, 185221.
Thomas R. Karl and Richard W. Knight, 1996. The 1995 Chicago Heat Wave:How Likely Is a Recurrence? BAMS url
KEVIN E. TRENBERTH, THOMAS R. KARL, AND THOMAS W. SPENCE, THE NEED FOR A SYSTEMS APPROACH TO CLIMATE OBSERVATIONS BAMS 2002 url
THOMAS C. PETERSON 2003 , Assessment of Urban Versus Rural In Situ Surface Temperatures in the ContiguousUnited States: No Difference Found J Cvlimate 2003. url