• Allsopp, D., 2004: History of the Digital Climate Archive. Extended Abstracts, Workshop on Climate Data Homogenization, Toronto, ON, Canada, Environment Canada, 1–11.

    • Search Google Scholar
    • Export Citation
  • Baker, G. B., 1975: Effect of observation time on mean temperature estimation. J. Appl. Meteor., 14 , 471476.

  • Belcher, B. N., , and A. T. DeGaetano, 2003: A method for operational detection of daily observation-time changes. J. Appl. Meteor., 42 , 18231836.

    • Search Google Scholar
    • Export Citation
  • Bootsma, A., 1976: A note on minimum temperature and the climatological day at first order stations. Atmosphere, 14 , 5355.

  • Byrd, G. P., 1985: An adjustment for the effect of observation time on mean temperature and degree-day computations. J. Climate Appl. Meteor., 24 , 869874.

    • Search Google Scholar
    • Export Citation
  • Cameron, T., , and H. Wilson, 1996: Minimum temperature bias introduced by a redefinition of the climatological day. Atmospheric Environment Service Internal Rep., Toronto, ON, Canada, 34 pp.

    • Search Google Scholar
    • Export Citation
  • DeGaetano, A. T., 1999: A method to infer observation time based on day-to-day temperature variations. J. Climate, 12 , 34433456.

  • Hutchinson, M. F., , D. W. McKenney, , K. Lawrence, , J. H. Pedlar, , R. F. Hopkinson, , E. Milewska, , and P. Papadopol, 2009: Development and testing of Canada-wide interpolated spatial models of daily minimum–maximum temperature and precipitation for 1961–2003. J. Appl. Meteor. Climatol., 48 , 725741.

    • Search Google Scholar
    • Export Citation
  • Janis, M. J., 2002: Observation-time-dependent biases and departures for daily minimum and maximum air temperature. J. Appl. Meteor., 41 , 588603.

    • Search Google Scholar
    • Export Citation
  • Karl, T. R., , C. N. Williams Jr., , and P. J. Young, 1986: A model to estimate the time of observation bias associated with monthly mean maximum, minimum and mean temperatures for the United States. J. Climate Appl. Meteor., 25 , 145160.

    • Search Google Scholar
    • Export Citation
  • Schaal, L. A., , and R. F. Dale, 1977: Time of observation temperature bias and “climatic change”. J. Appl. Meteor., 16 , 215222.

  • Vincent, L. A., , and D. W. Gullett, 1999: Canadian historical and homogeneous temperature datasets for climate change analyses. Int. J. Climatol., 19 , 13751388.

    • Search Google Scholar
    • Export Citation
  • Vincent, L. A., , X. Zhang, , B. R. Bonsal, , and W. D. Hogg, 2002: Homogenization of daily temperatures over Canada. J. Climate, 15 , 13221334.

    • Search Google Scholar
    • Export Citation
  • Vose, R. S., , C. N. Williams Jr., , T. C. Peterson, , T. R. Karl, , and D. R. Easterling, 2003: An evaluation of the time of observation bias adjustment in the U.S. Historical Climatology Network. Geophys. Res. Lett., 30 , 2046. doi:10.1029/2003GL018111.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 47 47 5
PDF Downloads 13 13 1

Bias in Minimum Temperature Introduced by a Redefinition of the Climatological Day at the Canadian Synoptic Stations

View More View Less
  • 1 Climate Research Division, Science and Technology Branch, Environment Canada, Toronto, Ontario, Canada
  • | 2 Custom Climate Services, Regina, Saskatchewan, Canada
  • | 3 Climate and Water Department, World Meteorological Organization, Geneva, Switzerland
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

On 1 July 1961, the climatological day was redefined to end at 0600 UTC (coordinated universal time) at all synoptic (airport) stations in Canada. Prior to that, the climatological day ended at 1200 UTC for maximum temperature and 0000 UTC for minimum temperature. This study shows that the redefinition of the climatological day in 1961 has created a cold bias in the annual and seasonal means of daily minimum temperatures across the country while the means of daily maximum temperatures were not affected. Hourly temperatures taken at 121 stations for 1953–2007 are used to determine the magnitude of the bias and its spatial variation. It was found that the bias is more pronounced in the eastern regions; its annual mean varies from −0.2° in the west to −0.8°C in the east. Not all days are affected by this change in observing time, and the annual percentage of affected days ranges from 15% for locations in the west to 38% for locations in the east. An approach based on hourly values is proposed for adjusting the affected daily minimum temperatures over 1961–2007. The adjustment on any individual day varies from 0.5° to 12.5°C. The impact of the adjustment is assessed by examining the trends in the annual mean of the daily minimum temperatures for 1950–2007. Overall, with the adjustment, the trends are becoming either more positive or are reversing from negative to positive, and they have changed by as much as 1°C in numerous locations in the eastern regions.

Corresponding author address: Lucie A. Vincent, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada. Email: lucie.vincent@ec.gc.ca

Abstract

On 1 July 1961, the climatological day was redefined to end at 0600 UTC (coordinated universal time) at all synoptic (airport) stations in Canada. Prior to that, the climatological day ended at 1200 UTC for maximum temperature and 0000 UTC for minimum temperature. This study shows that the redefinition of the climatological day in 1961 has created a cold bias in the annual and seasonal means of daily minimum temperatures across the country while the means of daily maximum temperatures were not affected. Hourly temperatures taken at 121 stations for 1953–2007 are used to determine the magnitude of the bias and its spatial variation. It was found that the bias is more pronounced in the eastern regions; its annual mean varies from −0.2° in the west to −0.8°C in the east. Not all days are affected by this change in observing time, and the annual percentage of affected days ranges from 15% for locations in the west to 38% for locations in the east. An approach based on hourly values is proposed for adjusting the affected daily minimum temperatures over 1961–2007. The adjustment on any individual day varies from 0.5° to 12.5°C. The impact of the adjustment is assessed by examining the trends in the annual mean of the daily minimum temperatures for 1950–2007. Overall, with the adjustment, the trends are becoming either more positive or are reversing from negative to positive, and they have changed by as much as 1°C in numerous locations in the eastern regions.

Corresponding author address: Lucie A. Vincent, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada. Email: lucie.vincent@ec.gc.ca

Save