Canadian Stations Research Articles

A Quality Assurance System for Canadian Hourly Pressure Data

Abstract In this study a comprehensive quality assurance (QA) system, which includes the hydrostatic check combined with a statistical homogeneity test, is designed and applied to hourly pressure records (for 1953–2002) from 761 Canadian stations, to produce a high-quality database of hourly station and sea level pressures for various climate studies. The main principles of the QA system are described in detail, followed by a brief emphasis on the error correction algorithms. The general performance of the QA system and the main problems in the Canadian historical hourly pressure database are discussed and illustrated through various examples. The results show that there are serious systematic errors (i.e., sudden changes in the mean, or mean shifts) in the Canadian hourly pressure database, which are caused either by the use of incorrect station elevation values in the reduction of barometer readings to station or sea level pressure values (e.g., the “50-ft rule” or station relocation without updates to the station elevation), by transposing/swapping station and sea level pressure values, or by mistakes made in the archive data ingestion or data recording/digitization processes (e.g., use of a wrong base number). Random errors also exist and are mainly due to the transposition of two digits or miscoding of one or two digits. These errors must be corrected before the data are used in various climate studies, especially climate change–related studies.

AutomatedSKSsplitting and upper-mantle anisotropy beneath Canadian seismic stations

SUMMARY We have developed an automated method for measuring shear wave splitting and applied it to SKS phases recorded at permanent broad-band stations in Canada. Our method performs two measurements, one seeking to minimize the energy on the transverse component, the other minimizing the smaller of two eigenvalues calculated from the covariance matrix of particle motion. A short-term-average/long-term-average (STA/LTA) phase picker is used to identify SKS arrivals and successive splitting measurements are made on incrementally larger windows around the SKS arrival. The final result is derived from the longest series of windows over which the splitting parameters remain constant. In this study we have processed over 20 000 station/event combinations from 34 stations and 1540 events. Roughly 2 per cent of the data produce reliable estimates of splitting, due to the stringent quality controls applied. We find good correlation between our results and previously published results from the same stations. At some stations we find significant differences in results between the two methods, an observation that has been verified using manual measurements. In each case, eigenvalue derived measurements are consistent with a single layer of anisotropy but transverse-energy derived results require a more complex interpretation. This discrepancy can be explained by misalignment of horizontal components. Tests with synthetic seismograms show that component misalignment can lead to false interpretations of multilayer or dipping anisotropy using the transverse-energy method. The quality of results at individual stations is variable, being influenced both by the volume of available data (determined by station deployment date and the distribution of natural seismicity), and the performance of the STA/LTA picker used to define the start of the SKS window. We compare the orientation of the inferred anisotropy at each station with local tectonic features and directions of absolute plate motion (APM); there is no consistent correlation. Many stations give results that agree with both, while some agree better with local geology and others agree better with APM directions. Results are available through a dedicated website and provide a potential aid to other studies of anisotropy in the deep Earth.

A River-wide Survey of Polychlorinated Biphenyls (PCBs), Polycylic Aromatic Hydrocarbons (PAHs), and Selected Organochlorine Pesticide Residues in Sediments of the Detroit River—1999

The spatial distribution of hydrophobic organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and octachlorostyrene (OCS) in sediments of the Detroit River was established using data from a 1999 river-wide survey. The survey employed a stratified random sampling design that divided the river into six geostatistical zones consisting of upper, middle, and lower U.S. and equivalent Canadian river reaches. Organic carbon normalized OCS sediment concentrations demonstrated no significant differences between U.S. or Canadian sediments or upstream/downstream gradients suggesting that OCS is derived primarily from sources upstream of the Detroit River. In contrast, sum PCBs and sum PAHs were significantly elevated at U.S. as compared to Canadian stations and demonstrated significant increasing upstream/downstream gradients in organic carbon normalized sediment contamination. The upper and middle U.S. river reaches contained a number of near-shore stations with high localized PCB and PAH sediment concentrations suggesting multiple inputs along the upper U.S. portion of the river. Consistent with past surveys, wide-spread sediment contamination of PCBs and PAHs continues to be observed in the highly industrialized Trenton Channel and downstream of Grosse Isle. Threshold effect level (TEL) sediment quality guidelines for PAHs and PCBs were exceeded in 92.6 and 77.8%, respectively, of stations in Trenton Channel and downstream of Grosse Isle. This large reservoir of degraded sediments in the lower U.S. river reach has the potential to enter Lake Erie during sediment disturbance events and likely contributes to gentoxic stress and increased bioaccumulation of PCBs in resident benthos, fish, and wildlife.

Climatology and trends in some adverse and fair weather conditions in Canada, 1953–2004

This study characterizes the climatology and trends of some adverse and fair weather occurrence in Canada, on the basis of reliable long‐term records of hourly weather and bright sunshine observations at about 90 Canadian stations for the period 1953–2004. The results show that fair or no‐weather (i.e., no precipitation or visibility obscuration) trends are generally consistent with the sunshine trends, showing significant increases in southern Canada, with decreases in the Canadian Arctic. The increase of no‐weather is most extensive in spring and summer, while the decrease is most extensive in autumn. For the same period, freezing precipitation has become more frequent in the region north of 50°N (especially in spring and autumn) but less frequent in southern British Columbia (BC), central Prairies, and the Great Lakes area in autumn‐winter, as well as in northeastern Canada in winter. Blowing snow occurrence has decreased significantly almost everywhere across Canada, with the most significant decline in southwestern Canada in winter. In every season, fog occurrence has significantly increased in the Prairies‐Yukon‐Northwest Territories and northern BC but decreased in eastern Canada and southern BC. The frequency of low ceiling conditions (<304.8 m, i.e., 1000 feet) has increased in Alberta‐BC interior and the Great Lakes area, with the most significant increases in Alberta‐BC interior in autumn‐winter and in the Great Lakes area in spring; while the other regions have experienced a negative trend, which prevails across the country in summer.

Polychlorinated biphenyls and polybrominated diphenyl ethers in the North American atmosphere

To assess the spatial concentration variability of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the atmosphere on a large continental scale, their annually integrated air concentrations were determined in 2000/2001 using XAD-based passive air samplers (PAS). The network included 40 stations in Canada, the United States, Mexico, Belize and Costa Rica, and covered 72 degrees of latitude and longitude. Total concentrations of PCB and PBDE congeners ranged from below the detection limit to 130 ng PAS −1 and 24 ng PAS −1, respectively. PCBs displayed a large variation between urban, rural and remote sites, whereas PBDEs did not follow such a pattern. Open burning of “Penta”-containing waste may have contributed to the PBDEs detected in the air samples from rural and remote areas. Air from the Canadian Arctic had a relatively higher percentage of lighter PCB congeners than air sampled in the tropical region, which is interpreted as evidence for global fractionation.

Observed Changes in Cyclone Activity in Canada and Their Relationships to Major Circulation Regimes

Abstract This study assessed the climate and trend of cyclone activity in Canada using mainly the occurrence frequency of cyclone deepening events and deepening rates, which were derived from hourly mean sea level pressure data observed at 83 Canadian stations for up to 50 years (1953–2002). Trends in the frequency of cyclone activity were estimated by logistic regression analysis, and trends of seasonal extreme cyclone intensity, by linear regression analysis. The results of trend analysis show that, among the four seasons, winter cyclone activity has shown the most significant trends. It has become significantly more frequent, more durable, and stronger in the lower Canadian Arctic, but less frequent and weaker in the south, especially along the southeast and southwest coasts. Winter cyclone deepening rates have increased in the zone around 60°N but decreased in the Great Lakes area and southern Prairies–British Columbia. However, extreme winter cyclone activity seems to have experienced a weaker increase in northwest-central Canada but a stronger decline in the Great Lakes area and in southern Prairies. The results also show more frequent summer cyclone activity with slower deepening rates on the east coast, as well as less frequent cyclone activity with faster deepening rates in the Great Lakes area in autumn. Cyclone activity in Canada was found to be closely related to the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and El Niño–Southern Oscillation (ENSO). Overall, cyclone activity in Canada is most closely related to the NAO. The simultaneous NAO index explains about 44% (41%) of the winter (autumn) cyclone activity variance in the east coast, 31% of winter cyclone activity variance in the 60°–70°N zone, and 17% of autumn cyclone activity variance in the Great Lakes area. Also, in several regions (e.g., the east coast, the southwest, and the 60°–70°N zone) up to 15% of the seasonal cyclone activity variance can be explained by the NAO/PDO/ENSO index one–three seasons earlier, which is useful for seasonal forecasting.

Evaluation of the stochastic weather generators LARS-WG and AAFC-WG for climate change impact studies

There is a need to know how well stochastic weather generators can produce daily climate scenarios for climate change impact studies. In this study, 2 stochastic weather generators (LARS-WG and AAFC-WG) were assessed, based on an experiment with historical daily climate data. The experiment was conducted for 3 stations in Canada, using 1911-1940 as the baseline climate period and 1971-2000 as the changed climate period. Weather generators were calibrated with the baseline data. Daily climate scenarios were then generated for 1971-2000, using parameters that were adjusted to reflect climate change. Different schemes for modifying weather generator parameters were assessed in relation to their capability to reproduce statistical properties of daily climate data for a changed climate. Using changes in the statistics of daily climate data between the baseline climate and the changed climate period, it became feasible to modify parameters for the weather generators that use empirical distributions. For reproducing changes in frequency of wet and dry spells, modification schemes with a full adjustment (all 2nd order transition probabilities being modified separately) for the 2nd order Markov chain appeared more effective than the modifi- cation to mean length of wet and dry spells. Separate adjustments for maximum (Tx) and minimum (Tn) temperature, rather than modification on the basis of changes in daily mean temperature, might also be necessary. The probability distribution of daily precipitation amount (P) in a changed climate seemed more difficult to simulate well, although the means and variances were produced better. In general, daily climate scenarios developed by weather generators can be reasonably reliable for agri- cultural impact studies, provided the changes in the statistics of daily weather variables from daily GCM output are reliable. Otherwise, downscaling may be required to obtain reliable changes in the statistics of local daily weather variables.

British or American?: Canada's ‘mixed’ broadcasting system in the 1930s

This article examines the role of independent commercial radio stations in Canada in the early 1930s. Canada's first public broadcaster, the Canadian Radio Broadcasting Commission, was created in 1932. It constructed a national network comprised of its own stations and time leased on many of the previously existing privately owned stations. A number of commercial stations, however, remained independent of all networks. It is argued here that for a brief period these stations were able to provide an alternative model of locally oriented community programming that could be characterized as truly popular.

A review of surface ozone background levels and trends

Abstract A survey of the literature was conducted to review historical and current surface ozone data from background stations in Canada, United States and around the world for the purpose of characterizing background levels and trends, present plausible explanations for observed trends and explore projections of future ozone levels. The annual ozone cycle at background sites in the Northern Hemisphere is characterized by a spring maximum, peaking during the month of May. Although presently there is no concensus as to the origin of the spring maximum, evidence supports both enhanced photochemistry in the free troposphere and stratospheric input. Modern day annual average background ozone concentrations over the midlatitudes of the Northern Hemisphere range between approximately 20–45 ppb, with variability being a function of geographic location, elevation and extent of anthropogenic influence. Annual median ozone levels at Canadian background stations fall between 23 and 34 ppb, a range similar to that reported for low-elevation background stations in the United States and around the world. Comparisons of ozone levels with those measured over a century ago indicate that current levels have increased by approximately two times. Although current trends are not uniform, there is some indication that background ozone levels over the midlatitudes of the Northern Hemisphere have continued to rise over the past three decades, and that this rise has been in the range of approximately 0.5–2% per year. Rising trends were steeper in the 1970s and 1980s compared to the 1990s, which have seen either a leveling off or a decline in the magnitude of these trends. Model sensitivity studies indicate that the rise in NO x emissions account for the greatest increase in background ozone levels over the past three decades. A substantial component of the background ozone concentration in western North America may be due to long-range transport of Asian pollution, especially during the spring months. Model projections using IPCC emission scenarios for the 21st century indicate that background ozone may rise to levels that would exceed internationally accepted environmental criteria for human health and the environment.

The Application of WGEN to Simulate Daily Climatic Data for Several Canadian Stations

Weather generators, like WGEN, are useful tools for generating synthetic daily data for application in water engineering, agriculture and climate change studies. In this research, the WGEN weather generator model is used to simulate daily maximum and minimum air temperature, precipitation and solar radiation for six major Canadian climate stations including Montreal, Quebec City, Ottawa, Toronto, Winnipeg and Vancouver. The WGEN-simulated daily data are then compared to observed daily data, so as to evaluate the performance of the WGEN model when applied to these stations. The results show that the comparisons between observed and WGEN-simulated data, in general, produce statistically significant correlations for maximum and minimum air temperature, solar radiation and precipitation.

Random regression analyses of feed intake of individually tested beef steers

Objective of the study was to apply random regression models to daily dry matter intakes (DMI) of 376 beef steers fed for up to 168 days for evaluating genetic parameters and the optimum period of test. Steers were tested in a research station in Canada from 1997 to 2001. Models included fixed effects of biological breed type, test group, herd of origin and starting age and random additive genetic and permanent environmental effects of animal. Legendre polynomials on days of test were fitted for all fixed and random effects, except for biological types, which were estimated as linear regression on biological type composition. Heritability substantially improved from the first week up to 84 days on test (0.23 to 0.49), when it reduced the rate of increase. Genetic correlation between cumulative feed intake in the entire period of test and the intake up to 84 days was high (0.93). Results indicated that a test period of 84 days could be used for evaluating cumulative feed intake of steers for a 168 days growth period. Genetic eigenfunctions revealed that changes to the shape of the feed intake curve seem to be more difficult than changes to the overall level of intake of steers.

Comparison of two fitting methods for the log‐logistic distribution

We investigate generalized probability weighted moments (GPWM) and maximum likelihood (ML) fitting methods in the two‐parameter log‐logistic (LL) model. Parameter and quantiles estimators are computed along with their asymptotic variances and covariances. A comparison of these methods is done by simulation. It is concluded that for estimating β, GPWM can provide better results than the ML method. However, for estimating quantiles, GPWM provides better results only for very small sample sizes, especially when the distribution is quite asymmetrical. Although presently, LL is not one of the distributions frequently used in hydrology, we agree with some authors that it merits wider use in hydrological practice. For a clearer idea on the merits of LL, we compare it with three other distributions for fitting flood data from 114 hydrometric stations in Canada. The results support our view regarding the good fitting potential of the LL distribution to extreme hydrologic data.

Linearized inverse scattering of teleseismic waves for anisotropic crust and mantle structure: 2. Numerical examples and application to data from Canadian stations

The objective of this study is to characterize elastic properties, including anisotropy, at the base of the crust and uppermost mantle using the Moho PMs phase recorded in the teleseismic P coda at Canadian stations. We use linearized inverse scattering and singular value decomposition to identify those parameter combinations to which idealized teleseismic data sets are most sensitive. Five to seven independent parameter combinations are likely to be resolvable, one of which is sensitive to isotropy, whereas the remainder quantify different harmonic orders (1θ, 2θ, 3θ) of back azimuthal response. Aside from the isotropic component which is resolved only by P‐SV interactions, P‐SV and P‐SH conversions exhibit a redundant sensitivity to model parameters for uniform back‐azimuthal sampling. We use parameter combinations from the idealized, uniform back‐azimuthal data distribution to compare Moho anisotropy at 25 broadband stations on the Canadian landmass. The isotropic component dominates at all stations and corresponds to shear velocity contrasts ranging between 10 and 35%. Perturbations to anisotropic material property parameters are more modest, generally between 3 and 7% when consistent between SV and SH responses and in many cases suggest an anisotropic lower crust. Inconsistent responses may manifest contamination by lateral heterogeneity, upper crustal reverberations, or pervasive crustal anisotropy leading to shear wave splitting.

The Canadian Updateable Model Output Statistics (UMOS) System: Validation against Perfect Prog

Abstract This paper describes validation tests of the Canadian Updateable Model Output Statistics (UMOS) system against the perfect prognosis forecast system and forecasts of weather elements from the operational numerical weather prediction model. Several update experiments were performed using 2-m temperature, 10-m wind direction and speed, and probability of precipitation as predictands. These experiments were designed to evaluate the ability of the UMOS system to provide improved forecasts during the period following a model change when the development samples contain data from two or more different model versions. Tests were run for about 200 Canadian stations for both summer and winter periods. Independent summer and winter samples were used in the evaluation, to compare UMOS forecast accuracy with the direct model output forecasts, the perfect prog forecasts, and MOS forecasts based only on data from the earlier model version. The authors were also able to compare the evaluation results of forecast...

North American weather‐type frequency and teleconnection indices

AbstractThe impact of teleconnections upon the surface climate has largely been examined via a response in monthly mean temperature or total precipitation. In this paper, a different approach is undertaken, by examining the response of synoptic weather‐type frequencies to different teleconnection phases.For over 330 stations in the USA and Canada, the Spatial Synoptic Classification scheme has classified each day in each station's period of record into one of seven weather‐type categories, based on thermal, moisture, and other characteristics. The differences in how frequently these different weather types occur in different phases of the North Atlantic Oscillation (NAO) and Pacific–North American (PNA) teleconnection patterns is assessed, for Canadian stations from 1953 to 1993, and for US stations from 1950 to 1999.For PNA, a significant shift in the transitional frequency is observed, suggesting changes in storm track. Concomitantly, a large shift in Dry Polar and Moist Tropical frequencies is observed across the continent. Across the West, in +PNA wintertime months far fewer Dry Polar days are observed. Across the eastern USA, these polar intrusions are more common, and Moist Tropical is diminished significantly.The frequency of the transitional situation is also correlated with NAO phase, with differences as large as a factor of two across much of Canada and the northern USA. In northeastern Canada, there is a large replacement of Moist Polar conditions with Dry Polar conditions during +NAO. Farther south, however, across the eastern USA, both polar weather types occur much less often with +NAO. Although previous research has discovered eastern North American connections to the NAO, this research has shown that the connections often extend into the interior West during much of the year. Particularly strong in the spring, Dry Tropical conditions are much more common with +NAO throughout much of the continent, as far west as the Great Basin. Copyright © 2003 Royal Meteorological Society.

Laboratory investigations of the response of Brewer‐Mast ozonesondes to tropospheric ozone

The Brewer‐Mast ozonesonde was used at Canadian stations from 1966 until 1980, when the Canadian network switched to the electrochemical concentration cell sonde. While the sondes appear to agree relatively well in the stratosphere, there is an evident discrepancy of 10–20% in tropospheric measurements [e.g., Tarasick et al., 1995, Figure 4]. Comparison of Brewer‐Mast sondes with a calibrated ozone source yields some interesting insight into this discrepancy. Sonde response is strongly dependent on the preflight preparation procedures employed. Although sondes prepared via procedures introduced in the 1980s [Claude et al., 1987] perform quite well, when prepared according to the procedures used in Canada in the 1970s, Brewer‐Mast sondes indicate 10–30% lower ozone than the calibrator. The following points are noted in particular: (1) a new Brewer‐Mast sonde shows a large (∼15%) increase in sensitivity between successive experiments; (2) especially at low (<100 ppb) O3 levels, the response even of previously flown sondes increases slowly with time; and (3) sondes show an additional slow increase of response with time that is apparently caused by ozone reactions with the phosphate buffer. The overall response curve indicated by 1, 2, and 3 implies that after correction to the observed total ozone, the earlier part of a flight would yield values that are too low, while the latter part would be too high. By applying a varying ozone input, simulating the typical variation in absolute ozone concentration experienced by a sonde in flight, we show that this can explain both the average correction factor (1.255) for the Canadian Brewer‐Mast record and the 10–20% discrepancy in tropospheric measurements.

Recent changes in wind chill temperatures at high latitudes in North America

Afternoon wind chill temperatures at fifteen Alaskan and northern Canadian stations in the months October through April have increased in most months and at most stations in the period 1953–1993 (that is, “apparent temperatures” have become warmer). Many monthly means increased by more than 5°C over the period. Though increases in air temperature had a dominant effect on increases in wind chill temperature, decreases in wind speed generally contributed to the wind chill temperature increases. The largest and most persistent positive trends in wind chill temperature were in Alaska and western Canada, with negative and smaller positive trends in central, eastern, and northern Canada. As a result of the trends, humans outdoors in the afternoon have experienced an “apparent” warming even larger than the warming indicated by the air temperature trends.

Chlordane enantiomers and temporal trends of chlordane isomers in arctic air.

A 14-year data set (1984-1998) for chlordane compounds in arctic airwas examined to discern temporal trends. trans-Chlordane (TC), cis-chlordane (CC), and trans-nonachlor (TN) declined significantly (p < 0.001-0.02), with apparent times for 50% reduction of 4.9-9.7 y. The isomer fraction of TC = (TC/(TC + CC) also declined significantly (p < 0.001 -0.014) over the same time period. The enantiomeric composition of TC and CC was determined in air samples collected at arctic stations in Canada (1993-1996), Russia (1994), and Finland (1998), and a temperate station on the Swedish west coast (1998). Enantiomer fractions, EF = (+)/[(+) + (-)], were significantly different from measured EFs of racemic standards (0.498-0.501) at all stations for TC (p < 0.001) and two stations for CC (p < 0.001 to <0.05). These observations suggest changing source composition of chlordane in arctic air, with a greater proportion of weathered residues in recent years, possibly derived from soils. Identification of nonracemic (mean EFs = 0.662-0.703) heptachlor exo-epoxide (HEPX) at the four air stations further exemplifies contributions of soil emissions to long-range transport of chlordane-related compounds.

Correlation studies of compressional Pc5 pulsations in space and Ps6 pulsations on the ground

Compressional Pc5 pulsations in space and Ps6 pulsations on the ground are common features observed in the morning sector. Here we use a conjunction study of Equator‐S, Geotail, and ground stations in Canada to show that Ps6 pulsations can be the ground counterpart of compressional Pc5 pulsations observed by satellites. Because strong Ps6 pulsations are associated with optical omega‐band signatures, we also suggest that the omega‐band counterparts in space might be compressional pulsations on the Pc5 scale. We also discuss the magnetic field configuration that makes all these observations consistent.

Long‐term variations of UV‐B irradiance over Canada estimated from Brewer observations and derived from ozone and pyranometer measurements

Routine uniform spectral UV‐B measurements with Brewer spectrophotometers in the Canadian network began in 1989. This relatively short duration of UV measurements militates against reliable detection of long‐term changes in UV. A statistical model has been developed to extend the record of UV back to the early 1960s. It estimates UV values (at individual wavelengths and spectrally integrated) from global solar radiation, total ozone, dew point temperature, and snow cover. The model results are demonstrated to be in good agreement with the measurements. For example, the standard deviation of the difference between monthly values of measured and derived erythemally weighted UV irradiation is 3.3% for summer months. The major source of error in the model estimates is probably linked to rare occurrences of absorbing aerosols in the atmosphere. Long records of reliable measurements of total ozone, global solar radiation, and other parameters made it possible to derive UV‐B values at three Canadian stations from the mid‐1960s. Trends in derived erythemally weighted UV at two stations (Toronto and Edmonton) are similar to those expected from total ozone trends although the estimated error of the UV trends is more than 2 times larger. However, the increase in annual UV at Churchill (59°N) in 1979–1997 was found to be more than twice that expected from the ozone decline. This is a result of longterm changes in snow cover and clouds.