Impact of Aligning Climatological Day on Gridding Daily Maximum–Minimum Temperature and Precipitation over Canada

Abstract

On 1 July 1961, the climatological day was redefined to end at 0600 UTC at all principal climate stations in Canada. Prior to that, the climatological day at principal stations ended at 1200 UTC for maximum temperature and precipitation and 0000 UTC for minimum temperature and was similar to the climatological day at ordinary stations. Hutchinson et al. reported occasional larger-than-expected residuals at 50 withheld stations when the Australian National University Spline (ANUSPLIN) interpolation scheme was applied to daily data for 1961-2003, and it was suggested that these larger residuals were in part due to the existence of different climatological days. In this study, daily minimum and maximum temperatures at principal stations were estimated using hourly temperatures for the same climatological day as local ordinary climate stations for the period 1953-2007. Daily precipitation was estimated at principal stations using synoptic precipitation data for the climatological day ending at 1200 UTC, which, for much of the country, was close to the time of the morning observation at ordinary climate stations. At withheld principal stations, the climatological-day adjustments led to the virtual elimination of large residuals in maximum and minimum temperature and a marked reduction in precipitation residuals. Across all 50 withheld stations the climatological day adjustments led to significant reductions, by around 12% for daily maximum temperature, 15% for daily minimum temperature, and 22% for precipitation, in the residuals reported by Hutchinson et al.

Rain-on-snow events over North America based on two Canadian regional climate models

“…This precipitation dataset was constructed based on observations from the National Oceanic and Atmospheric Administration (NOAA) Cooperative observer program (COOP) stations (Maurer et al 2002). The Hopkinson et al (2011) precipitation dataset covers the Canadian landmass south of 60°N at a spatial resolution of 0.1°. This Canadian dataset was developed from daily observations from Environment Canada's climate stations, using a thin plate smoothing spline surface fitting method (Hutchinson et al 2009).…”

Estimating daily mean temperature from synoptic climate observations

“…Thus, direct comparisons of these estimates between countries are not so easy. A change in the definition of the climate day can make differences of up to 20°C (Hopkinson et al, 2011) at a single station. Another difficulty with the max-min values is that when observations are not automated, the precision of the instrument is different from a regular thermometer, and it has to be taken out of the screen and reset every day, which can lead to drift in calibration, and stretches of missing values.…”

Hydrologic extremes – an intercomparison of multiple gridded statistical downscaling methods

“…• grid spacing (∼ 10 km) for daily minimum temperature, maximum temperature, and precipitation amounts for the period 1950-2010 by Hopkinson et al (2011) andMcKenney et al (2011). Station data from Environment Canada observing sites were interpolated onto the high-resolution grid using the ANUSPLIN smoothing splines with elevation, longitude, and latitude as interpolation predictors.…”