The effect of modernization of climate reference networks on continuity of daily maximum and minimum temperature observations

Climate monitoring network in Canada has declined rapidly since the early 1990s. Many stations were closed because of the changes in roles and priorities of previously cooperating departments and agencies; some stations were automated using various types of autostations. In order to preserve or restore continuity of climate observations at the sites designated as RCS (Reference Climate Network) and GSN, that is GCOS (Global Climate Observing System) Surface Network, the ‘Modernization of the Climate Observing Network' project was initiated several years ago. Standardized autostations that consist of Campbell Scientific data loggers and specially selected instrumentation have been installed at the affected climate reference sites. Since the main purpose of these networks is to detect climate trends and variability, it is important to assess the impact of modernization on continuity of observations. Whenever possible, an effort was made to collect at least 1 to 2 years of overlapping manned and automated observations that would help in computing systematic biases between the old and new sets of observations.

Concurrent observations are used to assess continuity of daily minimum and maximum temperatures records at modernized reference climate stations. The preliminary analysis is conducted using two methods. In the first technique (Milewska and Hogg, 2002), days with certain meteorological conditions, defined by sky cover and wind speed, are grouped together. Biases computed for each group emphasize instrumental and siting differences and are well suited for adjustment of daily values. The second technique, based on regression models that include a reference series from the surrounding stations, was developed to identify discontinuities in temperature time series caused by station relocation and changes in observing procedures (Vincent et al. 2002). A similar approach is used in this study to establish if the join of manned and automated observations has created an artificial discontinuity at the joining year and furthermore to determine if the daily adjustments are reliable to create a suitable temperature series. The results from both methods are compared.

References

Milewska, E. and W.D. Hogg. 2002. Continuity of climatological observations with automation. Atmosphere-Ocean 40(3): 333-359.

Vincent, L.A., X. Zhang, B.R. Bonsal and W.D. Hogg. 2002: Homogenization of daily temperatures over Canada. J. Climate 15: 1322-1334.