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Bulk Transfer Coefficients Estimated from Eddy-Covariance Measurements over Lakes and Reservoirs
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  • Sofya Guseva,
  • Fernando Armani,
  • Ankur Rashmikant Desai,
  • Nelson Luís Dias,
  • Thomas Friborg,
  • Hiroki Iwata,
  • Joachim Jansen,
  • Gabriella Lükő,
  • Ivan Mammarella,
  • Irina Repina,
  • Anna Rutgersson,
  • Katharina Scholz,
  • Uwe Spank,
  • Victor M Stepanenko,
  • Péter Torma,
  • Timo Vesala,
  • Andreas Lorke
Sofya Guseva
University Koblenz-Landau (Landau)

Corresponding Author:guseva@uni-landau.de

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Fernando Armani
Universidade Federal do Paraná
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Ankur Rashmikant Desai
University of Wisconsin-Madison
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Nelson Luís Dias
Federal University of Paraná
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Thomas Friborg
University of Copenhagen
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Hiroki Iwata
Shinshu University
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Joachim Jansen
Uppsala University
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Gabriella Lükő
Budapest University of Technology and Economics
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Ivan Mammarella
University of Helsinki
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Irina Repina
A.M. Obukhov Institute of Atmospheric Physics
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Anna Rutgersson
Uppsala University
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Katharina Scholz
University of Innsbruck
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Uwe Spank
Technical University of Dresden
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Victor M Stepanenko
Lomonosov Moscow State University
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Péter Torma
Budapest University of Technology and Economics
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Timo Vesala
University of Helsinki, Institute for Atmospheric and Earth System Research
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Andreas Lorke
University of Koblenz and Landau
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The drag coefficient (CDN), Stanton number (CHN) and Dalton number (CEN) are of particular importance for the bulk estimation of the surface turbulent fluxes of momentum, heat and water vapor at water surfaces. Although these bulk transfer coefficients have been extensively studied over the past several decades mainly in marine and large-lake environments, there are no studies focusing on their synthesis for many lakes. Here, we evaluated these coefficients through directly measured surface fluxes using the eddy-covariance technique over more than 30 lakes and reservoirs of different sizes and depths. Our analysis showed that generally CDN, CHN, CEN (adjusted to neutral atmospheric stability) were within the range reported in previous studies for large lakes and oceans. CHN was found to be on average a factor of 1.4 higher than CEN for all wind speeds, therefore, likely affecting the Bowen ratio method used for lake evaporation measurements. All bulk transfer coefficients exhibit substantial increase at low wind speeds (< 3 m s-1), which could not be explained by any of the existing physical approaches. However, the wind gustiness could partially explain this increase. At high wind speeds CDN, CHN, CEN remained relatively constant at values of 2 10-3, 1.5 10-3, 1.1 10 -3, respectively. We found that the variability of the transfer coefficients among the lakes could be associated with lake surface area or wind fetch. The empirical formula C=b1[1+b2exp(b3 U10)] described the dependence of CDN, CHN, CEN on wind speed well and it could be beneficial for modeling when coupling atmosphere and lakes.