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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D22102, doi:10.1029/2005JD005925, 2005

Examination of discontinuities in hourly surface relative humidity in Canada during 1953–2003

William A. van Wijngaarden

Physics Department, York University, Toronto, Ontario, Canada


Lucie A. Vincent

Climate Research Branch, Meteorological Service of Canada, Toronto, Ontario, Canada


Abstract

Hourly values of relative humidity recorded at 75 stations across Canada were examined. Data were checked for possible discontinuities arising because of changes in procedures and instruments. It was found that the replacement of the psychrometer by the dewcel has produced a decreasing step in relative humidity at a number of stations. The historical records were closely examined to retrieve the dewcel installation date, and a procedure based on regression models was applied to determine if it corresponds to a significant step. Results show that there are more stations experiencing a dewcel step in the winter than in the summer. Examination of the trends also reveals that the step often accentuates the decreasing trends originally observed during winter and spring. However, significant steps taken into account, it appears that the relative humidity still decreased by several percent in the spring during 1953–2003 in western Canada. It seems that the southern and coastal stations are not as much affected by this change of instruments.

Received 1 March 2005; accepted 6 September 2005; published 16 November 2005.

Keywords: discontinuities; relative humidity; climate change.

Index Terms: 1694 Global Change: Instruments and techniques; 1616 Global Change: Climate variability (1635, 3305, 3309, 4215, 4513); 3309 Atmospheric Processes: Climatology (1616, 1620, 3305, 4215, 8408); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513).

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Citation: van Wijngaarden, W. A., and L. A. Vincent (2005), Examination of discontinuities in hourly surface relative humidity in Canada during 1953–2003, J. Geophys. Res., 110, D22102, doi:10.1029/2005JD005925.