A North American Arctic Aerosol Climatology using Ground-based Sunphotometry

Bokoye, Amadou I.; Royer, A.; O’Neill, N. T.; McArthur, L. J. B.

doi:10.14430/arctic706

Cited by 37 publications

(13 citation statements)

References 56 publications

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“…The artic atmosphere is generally clear but frequently subjected to forest fires in Alaska. Jet streams also transport pollution from Asia or other source regions into this region (Bokoyé et al, 2002). Biome 1 (Boreal Euroasia) is represented by two AERONET sites but suffers from a lack of match-ups (N=11) and low variability of τ a in the blue (from 0.07 to 0.31).…”

Section: Aeronet Datamentioning

confidence: 99%

Evaluation of the MERIS aerosol product over land with AERONET

2008

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Abstract. The Medium Resolution Imaging Spectrometer (MERIS) launched in February 2002 on-board the EN-VISAT spacecraft is making global observations of top-ofatmosphere (TOA) radiances. Aerosol optical properties are retrieved over land using Look-Up Table (LUT) based algorithm and surface reflectances in the blue and the red spectral regions. We compared instantaneous aerosol optical thicknesses retrieved by MERIS in the blue and the red at locations containing sites within the Aerosol Robotic Network (AERONET). Between 2002 and 2005, a set of 500 MERIS images were used in this study. The result shows that, over land, MERIS aerosol optical thicknesses are well retrieved in the blue and poorly retrieved in the red, leading to an underestimation of the Angstrom coefficient. Correlations are improved by applying a simple criterion to avoid scenes probably contaminated by thin clouds. To investigate the weakness of the MERIS algorithm, ground-based radiometer measurements have been used in order to retrieve new aerosol models, based on their Inherent Optical Properties (IOP). These new aerosol models slightly improve the correlation, but the main problem of the MERIS aerosol product over land can be attributed to the surface reflectance model in the red.

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Section: Aeronet Datamentioning

confidence: 99%

Evaluation of the MERIS aerosol product over land with AERONET

2008

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“…The negative slope is linked to an inversion in temperature profile where temperature increases with altitude in the troposphere. These inversions are characteristic of the Arctic climate system [ Hoff , 1988; Bokoye et al , 2002] and may occur at lower latitudes that come under the influence of Arctic air masses in the winter season (e.g., Yarmouth). The separation limit in temperatures between the normal profile and the inversion profile is ∼260 K, which corresponds to a potential isothermal atmospheric temperature also observed by Hoff [1988].…”

Section: Intercomparison and Analysismentioning

confidence: 99%

“…Furthermore, atmospheric water vapor plays an important role in climatic processes such as the global hydrologic cycle through precipitation [ Hall and Manabe , 2000] and evapotranspiration and the radiative energy balance and its impact on clouds and aerosols [ Kay and Box , 2000]. Water vapor content feedback also appears to be a key element in Arctic climate that influences the global climate system [ Blanchet and Girard , 1994, 1995; Curry et al , 1995; Bokoye et al , 2002].…”

Section: Introductionmentioning

confidence: 99%

Multisensor analysis of integrated atmospheric water vapor over Canada and Alaska

et al. 2003

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[1] Atmospheric water vapor is a key parameter for the analysis of climatic systems (greenhouse gas effect), in particular over high latitudes where water vapor displays an important seasonal variability. The sparse spatial and temporal sampling of atmospheric water vapor observations across Canada needs to be improved. A series of instruments and methods including a 940-nm solar absorption band radiometer (R) and radiosonde (S) analysis from a numerical weather prediction model and a ground-based bi-frequency Global Positioning System (GPS) were used to evaluate the integrated atmospheric water vapor (IWV) at various sites in Canada and Alaska from a multiyear database. The IWV-R measurements were collected within the framework of the North American Sun Radiometry network (AERONET/AEROCAN). Intercomparisons between [IWV-GPS and IWV-S], [IWV-R and IWV-GPS], and [IWV-R and IWV-S]show root mean square (RMS) differences of 1.8, 1.9, and 2.2 kg m À2 , respectively. GPS meteorology appears to be the easiest approach to calibrate the solar radiometer water vapor band owing to its flexibility, and it allows us to overcome the Sun radiometry limitation in high-latitude areas like the Arctic. The sensitivity of the GPS retrieval to various parameters like GPS satellite constellation and meteorological data are discussed. The classical linear relationship between the surface temperature and the integrated weighted mean temperature profile needed for IWV-GPS retrieval may be significantly different for Arctic air masses compared with midlatitude air masses in the case of tropospheric temperature profile inversion. An ever-expanding multiyear (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) North American summer water vapor climatology, derived from AERONET/Canadian Sun Radiometer Network, is presented and analyzed, showing a mean value of 19.8 ± 6.1 kg m À2 and variations from 17 kg m À2 in Alaska to 23 kg m À2 in southeastern Canada. The results in Bonanza Creek, Alaska, show significant interannual variations with a peak in 1997, which may be linked to an El Niño event that occurred in the same year. Such a database may also be useful for climate model validation as shown for the Canadian Global Environmental Model (RMS difference of 3.4 kg m À2 ). In the end we show that, even if data are selected only for cloud-free atmospheres, there are no significant differences as compared with radiosonde climatology at Canadian Northwestern sites ( 3% relatively to Bonanza Creek summer mean value).

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“…The columnar optical and microphysical properties obtained with these instruments allow characterizing the aerosols (Bokoye et al, 2002;Aaltonen et al, 2006;Toledano et al, 2006;Rodríguez et al, in press;Zdun et al, 2011). However sun photometer data series are still short for the AERONET and GAW sites, compared to the long datasets available at Ny-Ålesund (Herber et al, 2002) or Barrow (Polissar et al, 1999), and other sites further south like Norrköping (Sweden).…”

Section: Introductionmentioning

confidence: 99%

Overview of sun photometer measurements of aerosol properties in Scandinavia and Svalbard

Toledano

Cachorro

Gausa

et al. 2012

Atmospheric Environment

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a b s t r a c tAn overview on the data of columnar aerosol properties measured in Northern Europe is provided. Apart from the necessary data gathered in the Arctic, the knowledge of the aerosol loading in nearby areas (e.g. sub-Arctic) is of maximum interest to achieve a correct analysis of the Arctic aerosols and transport patterns. This work evaluates data from operational sites with sun photometer measurements belonging either to national or international networks (AERONET, GAW-PFR) and programs conducted in Scandinavia and Svalbard. We enumerate a list of sites, measurement type and periods together with observed aerosol properties. An evaluation and analysis of aerosol data was carried out with a review of previous results as well. Aerosol optical depth (AOD) and Ångström exponent (AE) are the current parameters with sufficient long-term records for a first evaluation of aerosol properties. AOD (500 nm) ranges from 0.08 to 0.10 in Arctic and sub-Arctic sites (Ny-Ålesund: 0.09; Andenes: 0.10; Sodankylä: 0.08), and it is somewhat higher in more populated areas in Southern Scandinavia (AOD about 0.10e0.12 at 500 nm). On the Norwegian coast, aerosols show larger mean size (AE ¼ 1.2 at Andenes) than in Finland, with continental climate (AE ¼ 1.5 at Sodankylä). Columnar particle size distributions and related parameters derived from inversion of sun/sky radiances were also investigated. This work makes special emphasis in the joint and collaborative effort of the various groups from different countries involved in this study. Part of the measurements presented here were involved in the IPY projects Polar-AOD and POLARCAT.

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A North American Arctic Aerosol Climatology using Ground-based Sunphotometry

Cited by 37 publications

References 56 publications

Evaluation of the MERIS aerosol product over land with AERONET

Evaluation of the MERIS aerosol product over land with AERONET

Multisensor analysis of integrated atmospheric water vapor over Canada and Alaska

Overview of sun photometer measurements of aerosol properties in Scandinavia and Svalbard

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