L. J. B. McArthur

McMaster University, Hamilton, Ontario, Canada

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Publications (32)58.98 Total impact

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    V E Fioletov · L J B McArthur · T W Mathews · L Marrett
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    ABSTRACT: The file contains the 1-deg latitude by 1-deg longitude gridded dataset of UV estimates over the US and Canada. The data file includes the mean and 95th percentile values for hourly doses of vitamin D weighted UV for each month of the year, as well as the mean and 95th percentile values for the time in the sun required to get 1 SDD for six types of skin. The hourly mean and 95th percentile values of UV index (or erythemal UV) are also included in the file.
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    ABSTRACT: The sunphotometer Earth atmosphere measurement (SPEAM-I) experiment was flown on the United States space shuttle Challenger in October, 1984 as part of a group of Canadian experiments referred to as CANEX-I. Measurements of the solar intensity were made through the orbiter side-hatch window at various wavelengths in the visible and near-ultraviolet during a number of terminator crossings using a hand-held, interference filter photometer. Observations at 315 and 324 nm were analyzed to give vertical profiles of ozone at 63.34°S, 91.96°E. These profiles are compared with data from the literature. The success of this experiment points the way to the use of small instruments to make accurate but inexpensive observations of the composition of the upper atmosphere.
    Canadian Journal of Physics 02/2011; 69:1123-1127. DOI:10.1139/p91-171 · 0.93 Impact Factor
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    V E Fioletov · L J B McArthur · T W Mathews · L Marrett
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    ABSTRACT: Solar UV radiation is a major provider of vitamin D for humans. This study examines the distribution of solar UV radiation weighted according to the vitamin D action spectrum over the USA and Canada. Hourly and daily doses of spectrally integrated UV irradiance using the vitamin D action spectrum were estimated using a statistical relationship between UV irradiance and global solar irradiance, total ozone, and dew point temperature for 45 sites in Canada and 52 in the USA. Brewer spectrophotometer measurements at 12 sites in Canada and 21 sites in the USA were used to validate the obtained results. Different characteristics of the vitamin D action spectrum-weighted UV irradiance distribution over North America are presented in the form of monthly maps and as a data file. The time required to obtain standard vitamin D dose is also calculated for six types of skin.
    Journal of photochemistry and photobiology. B, Biology 08/2010; 100(2):57-66. DOI:10.1016/j.jphotobiol.2010.05.002 · 2.80 Impact Factor
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    ABSTRACT: Aerosol optical depth (AOD) measurements were acquired at six Arctic sunphotometer sites during the ARCTAS-A (April, 2008) campaign. Numerous smoke events were identified and related to extensive forest and agricultural fires in eastern Russia and northern Kazakhstan/southwestern Russia respectively. An analysis of the fine (sub-micron) optical depths from the six stations indicated the presence of underlying low frequency trends which were coherent with general meteorological considerations, source information, model estimates and remote sensing information. Low frequency (diurnal) coarse-mode optical depth events were observed at a number of the stations; these singular events are likely due to ice particles whose nucleation may have been associated with the presence of smoke, or possibly dust. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
    Geophysical Research Letters 03/2010; 37(5). DOI:10.1029/2009GL041375 · 4.46 Impact Factor
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    J. A. DAVIES · R. SCHROEDER · L. J. B. McARTHUR
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    ABSTRACT: Spectral optical depth measurements at Hamilton, Ontario in 1981 and 1983 are used to estimate stratospheric aerosol optical depths and a particle size distribution for the period of maximum stratospheric perturbation by aerosol due to the El Chichon eruption. Results are generally in good agreement with high altitude measurements and estimates. On average, stratospheric optical depth increased by about 0.08 with little spectral variation. Maximum aerosol enhancement occurred between January and May 1983. Mean optical depths for this period were inverted by the constrained linear inversion method of King. The resulting size distribution was similar to the haze H form of the incomplete distribution. It compared favourably with a distribution obtained by inverting NASA CV990 optical depth measurements and was similar to estimates based on direct aerosol measurements by aircraft and balloon.
    Tellus B 01/2010; 40B(2):154 - 160. DOI:10.1111/j.1600-0889.1988.tb00219.x · 3.76 Impact Factor
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    ABSTRACT: We describe aerosol optical depth (AOD) measured during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) experiment, conducted in North America in April and June–July 2008, focusing on vertical profiles, inter-comparison with correlative observations, fine-mode fraction and horizontal variability. The AOD spectra spanning 354–2139 nm measured with the 14-channel Ames Airborne Tracking Sunphotometer (AATS-14) are generally less wavelength-dependent below 2 km (499-nm Angstrom exponent 1.4 ± 0.3) than in 2–4 km (1.6–1.8) for Alaska in April 2008. Together with concurrent aerosol mass spectrometry and black carbon incandescence measurements, this corroborates the hypothesis that Arctic haze in these layers originates mainly from anthropogenic emission and biomass burning, respectively. The spectra are within 3%+0.02 of the vertical integral of local visible-light scattering and absorption for two thirds of the 55 vertical profiles examined. The horizontal structure of smoke plumes in central Canada in June and July 2008 explains most outliers. The differences in mid-visible Angstrom exponent are 0.1. The retrieved fine-mode fraction of AOD is mostly between 0.7 and 1.0, and its root mean square difference from column-integral submicron fraction (measured with nephelometers, absorption photometers and an impactor) is 0.12. These AOD measurements from the NASA P-3 aircraft, after compensation for below-aircraft light attenuation by vertical extrapolation, mostly fall within 0.02 of AERONET ground-based measurements for five overpass events. Evidently, the fresh local emission in Canada in June and July makes the horizontal distribution of AOD highly heterogeneous (standard deviation ~19% of the mean over 20 km) and random (autocorrelation r=0.37 across 20 km), in contrast to long-range transport to Alaska in April (std~2%, r=0.95). The variability observed over 6 km is noticeably smaller (std~9%, r=0.71). The decrease represents the reduction in collocation error that remote sensing can potentially achieve by improving resolution for ARCTAS Canada and similar environments.
    Atmospheric Chemistry and Physics 01/2010; DOI:10.5194/acpd-10-18315-2010 · 4.88 Impact Factor
  • A. Saha · N. O'Neill · K. Latha · L. McArthur · K. Strawbridge
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    ABSTRACT: The Kasatochi volcano (52.17 N, 175.51 W; 314 m above m.s.l) in the Aleutian island in Alaska unleashed a powerful eruption on August 7, 2008 as reported by the Alaska Volcano Observatory (http://avo.alaska.edu/activity/Kasatochi.php). Ground-based sun photometer measurements from AEROCAN / AERONET network stations, along with remote sensing imagery products (CALIPSO, MODIS, OMI) and Back trajectories (HYSPLIT model) was used to analyze, map and track the volcanic plume. Calipso and ground- based lidar profiles of attenuated backscatter and depolarization ratio over North America show that the volcanic plume was present over a significant portion of the upper troposphere and lower stratosphere.
    AGU Spring Meeting Abstracts; 05/2009
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    V E Fioletov · L J B McArthur · T W Mathews · L Marrett
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    ABSTRACT: Erythemally weighted solar ultraviolet (UV) radiation is often used to characterize the production of vitamin D in a human body. However, the vitamin D production action spectrum is different than that for erythemal UV. The vitamin D action spectrum weighted UV is more sensitive to UV-B, while the erythemal UV action spectrum has higher weighting coefficients than the vitamin D action spectrum in the UV-A part of the spectrum. Therefore, by using the erythemal UV as an estimate for the vitamin D action spectrum weighted UV can give results that differ by up to a factor of 5. This study examines the relationship between erythemal and vitamin D action spectrum weighted UV radiation using measurements of spectral UV at the surface by Brewer spectrophotometers that are part of the US and Canadian observational networks. It is shown that the ratio of vitamin D action spectrum weighted UV to erythemal UV is nearly constant for high levels of UV (UV Index greater than 5.5) and therefore vitamin D action spectrum weighted UV can be described in terms of erythemal UV. For lower levels of UV though this relationship should not be used. A simple formula that calculates vitamin D action spectrum weighted UV from UV Index is developed. An empirical formula that expresses the ratio of vitamin D action spectrum weighted UV to erythemal UV as a function of the solar zenith angle and column ozone is also suggested. The geographical distributions of vitamin D action spectrum weighted UV in the US and Canada are discussed.
    Journal of photochemistry and photobiology. B, Biology 04/2009; 95(1):9-16. DOI:10.1016/j.jphotobiol.2008.11.014 · 2.80 Impact Factor
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    ABSTRACT: Numerous fine mode (sub-micron) aerosol optical events were observed during the summer of 2007 at the High Arctic atmospheric observatory (PEARL) located at Eureka, Nunavut, Canada. Half of these events could be traced to forest fires in southern and eastern Russia and the Northwest Territories of Canada. The most notable findings were that (a) a combination of ground-based measurements (passive sunphotometry, high spectral resolution lidar) could be employed to determine that weak (near sub-visual) fine mode events had occurred, and (b) this data combined with remote sensing imagery products (MODIS, OMI-AI, FLAMBE fire sources), Fourier transform spectroscopy and back trajectories could be employed to identify the smoke events.
    Geophysical Research Letters 01/2008; 35(14). DOI:10.1029/2008GL033733 · 4.46 Impact Factor
  • J J Michalsky · C A Gueymard · P Kiedron · L J B McArthur · R Philipona · T Stoffel
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    ABSTRACT: Atmospheric radiative transfer model estimates of diffuse horizontal broadband shortwave (solar) irradiance have historically been larger than measurements from a shaded pyranometer. A reference standard for the diffuse horizontal shortwave irradiance does not exist. There are no current efforts to develop an absolute standard that are known to the authors. This paper presents the case for a working standard for this measurement. Four well-behaved pyranometers from two previous intensive observation periods (IOP) were chosen for this study. The instruments were characterized for spectral and angular response before the IOP and calibrated during the IOP using a shade/unshade technique with reference direct irradiance from an absolute cavity radiometer. The results of the comparison and detailed analyses to explain the differences suggest selecting three of the four for the working standard. The 95% confidence uncertainty in this standard is estimated at 2.2% of reading + 0.2 W/m2. In lieu of a comparison to this trio, a procedure for obtaining low-uncertainty diffuse horizontal shortwave irradiance is suggested.
    Journal of Geophysical Research Atmospheres 01/2007; 112D:doi:10.1029/2007JD008651. DOI:10.1029/2007JD008651 · 3.44 Impact Factor
  • L J B McArthur · D I Wardle · C T McElroy · J B Kerr
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    ABSTRACT: The use of self-scanning photodiode arrays is well established for low light intensity multi-spectral measurement systems such as those used in spectroscopy and astronomy. Using the newly developed EG&G Reticon random access self-scanning linear photodiode array, an instrument has been developed for solar observations which overcomes the difficulties associated with these detectors at high light levels. By coupling this technology with flat-field concave holographic grating technology from American Holographic, a "sunphotospectrometer" has been built. This instrument is presently able to scan 1 024 channels of spectral information in less than 1 s. A prototype instrument is being tested with a second-generation version expected to fly aboard the US Space Shuttle within the next two years. The design of this instrument is described and preliminary spectra are presented to illustrate the measurement of NO2 using this portable system.
    Metrologia 01/2005; 28(3):291. DOI:10.1088/0026-1394/28/3/037 · 2.04 Impact Factor
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    ABSTRACT: The first intensive observation period (IOP) to simultaneously measure diffuse horizontal shortwave irradiance (scattered solar radiation that falls on a horizontal surface) with a wide array of shaded pyranometers suggested that a consensus might be reached that would permit the establishment of a standard with a smaller uncertainty than previously achieved. A second IOP has been held to refine the first IOP measurements using a uniform calibration protocol, offset corrections for all instruments and validation of those corrections, improvements in some of the instruments, and better data acquisition. The venue for both IOPs was the Department of Energy's Atmospheric Radiation Measurement (ARM) central facility in northern Oklahoma. The nine days of measurements in October 2003 included a better mixture of clear and overcast conditions than during the first IOP and revealed considerable differences among the instruments responses for different cloud conditions. Four of the 15 instruments were eliminated as candidates to be included in the standard because of noisy signals, inadequate offset correction, or instability with respect to the majority of the measurements. Eight pyranometers agreed to within {+-}2% for clear-sky conditions. Three others have a high bias on clear days relative to these eight, but all eleven agree within {+-}2% on overcast days. The differences and causes of this behavior under clear and cloudy skies are examined.
    01/2005; 110D. DOI:10.1029/2004JD005265
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    ABSTRACT: [1] Long-term monthly mean UV index values for Canada and the United States were calculated using information from two sources: from noon erythemal UV estimated from Total Ozone Mapping Spectrometer (TOMS) total ozone and reflectivity data and from UV index values derived from observations of global solar radiation, total ozone, dew point, and snow cover. The results are presented as monthly maps of mean noon UV index values. Mean UV index values in summer range from 1.5 in the Arctic to 11.5 over southern Texas. Both climatologies were validated against spectral UV irradiance measurements made by Brewer spectrophotometers. With snow on the ground the TOMS-based data underestimate UV by up to 60% with respect to Brewer measurements and UV derived from global solar radiation and other parameters. In summer, TOMS UV index climatology values are from 10 to 30% higher than those derived from global solar radiation and other parameters. The difference is probably related to aerosol absorption and pollution effects in the lower troposphere that are not currently detected from space. For 21 of 28 midlatitude Brewer sites, long-term mean summer UV measured values and UV derived from global solar radiation and other parameters agree to within +5 to −7%. The remaining seven sites are located in “clean” environments where TOMS estimates agree with Brewer measurements while UV derived from global solar radiation and other parameters is 10–13% lower. Brewer data also demonstrate that clean and “typical” sites can be as little as 70–120 km apart.
    Journal of Geophysical Research Atmospheres 11/2004; 109(D22). DOI:10.1029/2004JD004820 · 3.44 Impact Factor
  • D.A Finch · W.G Bailey · L.J.B McArthur · M Nasitwitwi
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    ABSTRACT: Global solar radiation (K↓) and photosynthetically active radiation (PAR) were measured at Lusaka, Zambia from April to December 2000. Daily K↓ and PAR followed a similar trend and the seasonal cycle was primarily determined by extraterrestrial radiation and cloudiness. The daily PAR/K↓ ratio also exhibited seasonal variation. The mean daily ratio was 1.992 mol MJ−1; the maximum daily ratio was 2.414 mol MJ−1 and the minimum daily ratio was 1.778 mol MJ−1. Generally, high PAR/K↓ ratios were associated with low clearness indices and low ratios with high clearness indices. The maximum daily ratio occurred in December, when dense cloud associated with the intertropical convergence zone (ITCZ) prevailed. The minimum daily ratio occurred in September when predominantly cloudless conditions, associated with the subtropical highs, coincided with regional biomass burning enhancements to atmospheric turbidity.
    Agricultural and Forest Meteorology 04/2004; 122(3):229-238. DOI:10.1016/j.agrformet.2003.09.015 · 3.89 Impact Factor
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    D. A. Finch · W. G. Bailey · L. J. B. McArthur · M. Nasitwitwi
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    ABSTRACT: Hourly UV Index values at 45 sites in Canada and 52 in the USA were estimated using a statistical relationship between UV irradiance and global solar radiation, total ozone, and dew point temperature. The estimation method also takes into account the enhancement of UV irradiance by snow using an empirical correction derived from Brewer UV measurements. Different characteristics of the UV Index distribution over North America were estimated from the derived UV irradiance for the period 1979-1987 and then presented in the form of monthly maps. Brewer UV measurements at 11 Canadian and 20 US sites and erythemal UV estimates from TOMS data were used for validation. Direct comparisons with Brewer measurements at 7 Canadian sites for the period in the 1990s when both pyranometer and spectral UV data were available demonstrated agreement within 2-3 percent except for periods of melting snow when variations in snow albedo yield higher errors in the derived UV irradiance.
    Proceedings of SPIE - The International Society for Optical Engineering 11/2003; DOI:10.1117/12.505921 · 0.20 Impact Factor
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    ABSTRACT: An improved understanding of the global ultraviolet (UV) climate has recently become of great interest. A number of stations are now making regular measurements of spectrally‐resolved UV‐B irradiance. Despite the lack of long‐term records, it is possible to describe many of the short‐term characteristics, dependencies and climatology of surface UV‐B irradiance. This article describes the current state of UV‐B measurements, and a climatology of surface UV‐B irradiance with particular focus on Canada. The dependence of UV irradiance on ozone and other climate variables is discussed in detail, with reference to observations. In addition, comparison of radiative transfer models with recent measurements indicates that it is possible to infer surface UV‐B irradiance from older records of total ozone and ancillary measurements (spectrally‐integrated irradiance, aerosol optical depth and surface albedo) permitting the derivation of longer‐term trends.
    Atmosphere-ocean 06/2003; 41:121-138. DOI:10.3137/ao.410202 · 1.19 Impact Factor
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    V. E. Fioletov · J. B. Kerr · L. J. B. McArthur · D. I. Wardle · T. W. Mathews
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    ABSTRACT: Hourly UV index values at 45 sites in Canada were estimated using a statistical relationship between UV irradiance and global solar radiation, total ozone, and dewpoint temperature. The estimation method also takes into account the enhancement of UV irradiance by snow using an empirical correction derived from Brewer UV measurements. Different characteristics of UV index distribution over Canada were estimated from the derived UV irradiance for the period 1979-87 and then presented in the form of monthly maps. Direct comparisons of Brewer measurements at seven Canadian sites with derived UV irradiance show agreement within 2%-3% except for periods of melting snow when variations in snow albedo yield higher errors in the derived UV irradiance.
    Journal of Applied Meteorology and Climatology 03/2003; 42(3):417-433. DOI:10.1175/1520-0450(2003)042<0417:EUICOC>2.0.CO;2 · 2.10 Impact Factor
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    ABSTRACT: Measurements of aerosol optical depth have become more numerous since the mid-1990s with the onset of commercially available, high-quality, low-maintenance automatic instrumentation. The development of several networks for aerosol measurements, and the next day availability of preliminary data for some, have further enhanced interest in the products this type of measurement can provide. With several networks operating globally and others operating either regionally or continentally within North America the comparability of the data emanating from the various archive centers is an important issue. The Bratt's Lake Observatory operates four separate types of Sun photometers in conjunction with three different networks: Aerosols in Canada, Global Atmosphere Watch, and the U.S. Department of Agriculture UV-B Monitoring Program. Data collected during the summer of 2001, following the protocols established by the networks and the Meteorological Service of Canada, were analyzed to determine the comparability among these networks. As the instruments and conversion algorithms are similar to other networks from around the globe, it is believed that the results of this comparison can be transferred, at least in part, to other operational networks. The results of the 3-month study indicate that the data obtained from the networks that operate direct-pointing instruments are very comparable, being within ±0.01 of an optical depth for instantaneous measurements during cloud-free line-of-sight conditions. Over the length of the comparison the root mean square difference of aerosol optical depth at 500 nm between the direct sun-pointing instruments was 0.0069. The rotating shadowband instruments did not perform as well. These results indicate that the data from well-maintained networks of direct sun-pointing photometers can provide data of the quality necessary to compare stations from across the globe.
    Journal of Geophysical Research Atmospheres 01/2003; 108. DOI:10.1029/2002JD002964 · 3.44 Impact Factor
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    ABSTRACT: The first intensive observation period (IOP) dedicated exclusively to the measurement of diffuse horizontal shortwave irradiance was held in the Fall 2001 at the central facility of the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site with the cooperation of the Baseline Surface Radiation Network (BSRN) community. The purpose of the study was to compare diffuse irradiance measurements among most commercial pyranometers and a few prototypes calibrated independently using current practices. The hope was to achieve a consensus for this measurement with the goal of improving the uncertainty of shortwave diffuse irradiance measurements. All diffuse broadband measurements were made using the same type of two-axis tracker with the direct beam blocked by shading balls. Tracking was excellent during the IOP with no lost data associated with tracker problems. Fourteen simultaneous measurements were obtained over a two-week period under mostly clear skies with low to moderate aerosol loading. Totally overcast data were obtained during the morning of one day. Five of the measurements are reproducible to about 2 W/m2 at the 95% confidence level. Three more agree with the mean of these five to about 4 W/m2 at the 95% confidence level after correction for thermal offsets.
    Journal of Geophysical Research Atmospheres 01/2003; 108. DOI:10.1029/2002JD002825 · 3.44 Impact Factor

Publication Stats

531 Citations
58.98 Total Impact Points

Institutions

  • 2010
    • McMaster University
      Hamilton, Ontario, Canada
  • 1999–2010
    • Environment Canada
      Montréal, Quebec, Canada
  • 2003
    • Correctional Service of Canada
      Ottawa, Ontario, Canada
  • 1029–2003
    • Servei Meteorològic de Catalunya
      Barcino, Catalonia, Spain