Ewa J. Milewska

Development and Testing of Canada-Wide Interpolated Spatial Models of Daily Minimum–Maximum Temperature and Precipitation for 1961–2003

Abstract The application of trivariate thin-plate smoothing splines to the interpolation of daily weather data is investigated. The method was used to develop spatial models of daily minimum and maximum temperature and daily precipitation for all of Canada, at a spatial resolution of 300 arc s of latitude and longitude, for the period 1961–2003. Each daily model was optimized automatically by minimizing the generalized cross validation. The fitted trivariate splines incorporated a spatially varying dependence on ground elevation and were able to adapt automatically to the large variation in station density over Canada. Extensive quality control measures were performed on the source data. Error estimates for the fitted surfaces based on withheld data across southern Canada were comparable to, or smaller than, errors obtained by daily interpolation studies elsewhere with denser data networks. Mean absolute errors in daily maximum and minimum temperature averaged over all years were 1.1° and 1.6°C, respectiv...

Customized Spatial Climate Models for North America

Over the past two decades, researchers at Natural Resources Canadas Canadian Forest Service, in collaboration with the Australian National University (ANU), Environment Canada (EC), and the National Oceanic and Atmospheric Administration (NOAA), have made a concerted effort to produce spatial climate products (i.e., spatial models and grids) covering both Canada and the United States for a wide variety of climate variables and time steps (from monthly to daily), and across a range of spatial resolutions. Here we outline the method used to generate the spatial models, detail the array of products available and how they may be accessed, briefly describe some of the usage and impact of the models, and discuss anticipated further developments. Our initial motivation in developing these models was to support forestry-related applications. They have since been utilized by a wider range of agencies and researchers. This article is intended to further raise awareness of the strengths and weaknesses of these clim...

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

AbstractOn 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 UT...

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

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 ad...

Optimizing Input Data for Gridding Climate Normals for Canada

AbstractSpatial models of 1971–2000 monthly climate normals for daily maximum and minimum temperature and total precipitation are required for many applications. The World Meteorological Organization’s recommended standard for the calculation of a normal value is a complete 30-yr record with a minimal amount of missing data. Only 650 stations (~16%) in Canada meet this criterion for the period 1971–2000. Thin-plate smoothing-spline analyses, as implemented by the Australian National University Splines (ANUSPLIN) package, are used to assess the utility of differing amounts of station data in estimating nationwide monthly climate normals. The data include 1) only those stations (1169) with 20 or more years of data, 2) all stations (3835) with 5 or more years of data in at least one month, and 3) as in case 2 but with data adjusted through the most statistically significant linear-regression relationship with a nearby long-term station to 20 or more years (3983 stations). Withheld-station tests indicate that...

Preserving Continuity of Long-Term Daily Maximum and Minimum Temperature Observations with Automation of Reference Climate Stations using Overlapping Data and Meteorological Conditions

ABSTRACT The seasonal-by-wind bias method for aligning time series of daily maximum and minimum temperatures from past conventional staffed and new automated sites using closely collocated, overlapping observations is presented for twenty-two modernized Reference Climate Stations in Canada. The method consists of adjusting for incompatible observing times and deriving biases from the daily “manual-minus-automated” temperature differences classified into seasons and wind-speed conditions. Most of the biases vary with the season, and many show limited wind dependency. Four sets of adjusted time series are prepared based on two-year and five-year overlapping data and on seasonal bias with or without wind conditions; the adjusted data are compared with the original observations. Based on the mean of the absolute differences and examination of box plots, the results show that, for this particular set of stations, the two-year versus five-year and seasonal versus seasonal-by-wind bias adjusted time series are overall similar. The largest contribution to the improvements in the adjusted observations came from matching the times of observation. Additionally, daily temperatures are adjusted using statistical methods applied with neighbouring station data but no overlapping observations at collocated stations; it is concluded that these do not necessarily resolve the bias between staffed and automated sites.

Potential and Limitations of Using Satellite Data to Evaluate the Spatial Detail in Climatological Air Temperature Maps

Abstract Detailed patterns of spatial variability in surface temperature can be observed with the use of thermal infrared data from satellites. A method is developed to use clear‐sky thermal infrared satellite data to evaluate traditional monthly average maximum air temperature maps interpolated from observations at surface stations using a statistical thin plate smoothing spline method. Results of comparisons over Alberta, Manitoba and Saskatchewan from June to October, for the years 2001 to 2005, are presented. The satellite data allow identification of some limitations in the interpolation technique at high altitudes in mountain ranges and in data‐sparse areas due to low station density. In the data‐sparse areas, the highest discrepancies could be linked to the unrepresentativeness of the stations because of different land cover or the presence of water bodies. Conversely, the interpolated air temperature maps allow the identification of problems with using thermal infrared data to estimate near‐surface air temperatures in areas of significant moisture deficit and at the locations of water bodies.

Cloud type observations and trends in Canada, 1953–2003

Abstract The monitoring of cloud amount and type in Canada is discussed in detail, including observing, archiving, data transmission procedures and practices, and automation. There have been some major monitoring challenges since 1953. In 1977, the network‐wide replacement of detailed cloud layer amounts and obscuring phenomena by broad sky conditions, based on summation amounts, imposed analysis of frequency of occurrence of mainly cloudy conditions rather than actual amounts. Partial automation with Automated Weather Observing Systems resulted in the cessation of observations of higher clouds and cloud types, as well as the incompatibility of sky coverage with human observations at eight percent of stations. For every hourly report from eighty‐four airport stations from 1953 to 2003, each layer is classified according to cloud type and related standard base height into three levels of low, middle, and high clouds. Trends in occurrence of summation amounts of mainly cloudy conditions at each of these three levels are computed on annual, seasonal, daytime and nighttime scales, together with annual trends in occurrence of selected convective and stratiform clouds. Based on annual anomalies averaged over the country and provinces, no major network‐wide systematic discontinuities were noted; on average, on an annual basis over the entire network, slight decreasing trends are noted for summation amounts of mainly cloudy conditions at low and middle levels, and increasing trends at high levels. The increasing trend at high levels is indeed remarkable. The rate of increase, especially rapid until 1974, has been shown to be caused by a prominent increase in cirrus cloud reports. The link between this rise and the increase in air traffic was established by others in the United States.. This link may also apply in Canada, which experienced a similar expansion in aviation. Notably, the largest increase in high nighttime cloudiness and decrease in low‐middle cloudiness is evident in western Canada, possibly contributing to the recently observed warming of daily minimum and maximum temperatures there. The occurrence of stratiform clouds at all levels exhibits significant decreasing trends across the country, except for southern Ontario. Clouds of intense convection show pronounced decreasing trends in western Canada, while not much change is evident elsewhere. Similar to cirrus, stratocumulus is notable as it shows strong positive trends everywhere in the country. On the other hand combined stratus and stratus fractus clouds exhibit decreasing trends, except over British Columbia where the opposite occurs. The findings concerning stratocumulus, stratus and stratus fractus clouds in Canada are similar to the findings in the United States.