de Groot Henk W.

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de Groot
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Henk W.
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  • Article
    Relaxed eddy accumulation measurements of the sea-to-air transfer of dimethylsulfide over the northeastern Pacific
    (American Geophysical Union, 2004-01-30) Zemmelink, Hendrik J. ; Gieskes, Winfried W. C. ; Klaassen, Wim ; Beukema, Wim J. ; de Groot, Henk W. ; Baar, Hein J. W. de ; Hintsa, Eric J. ; McGillis, Wade R. ; Dacey, John W. H.
    Gas transfer rates were determined from relaxed eddy accumulation (REA) measurements of the flux of dimethylsulfide (DMS) over the northeastern Pacific Ocean. This first application of the REA technique for the measurement of DMS fluxes over the open ocean produced estimates of the gas transfer rate that are on average higher than those calculated from commonly used parameterizations. The relationship between the total gas transfer rate and wind speed was found to be gas kgas = 0.53 (±0.05) U102. Because of the effect of the airside resistance, the waterside transfer rate was up to 16% higher than kgas. Removal of the airside transfer component from the total transfer rate resulted in a relation between wind speed and waterside transfer of k660 = 0.61 (±0.06) U102. However, DMS fluxes showed a high degree of scatter that could not readily be accounted for by wind speed and atmospheric stability. It has to be concluded that these measurements do not permit an accurate parameterization of gas transfer as a function of wind speed.
  • Article
    Fluxes and gas transfer rates of the biogenic trace gas DMS derived from atmospheric gradients
    (American Geophysical Union, 2004-06-30) Zemmelink, Hendrik J. ; Dacey, John W. H. ; Hintsa, Eric J. ; McGillis, Wade R. ; Gieskes, Winfried W. C. ; Klaassen, Wim ; de Groot, Henk W. ; Baar, Hein J. W. de
    Gas transfer rates were determined from vertical profile measurements of atmospheric dimethylsulfide (DMS) gradients over the equatorial Pacific Ocean obtained during the GasEx-2001 cruise. A quadratic relationship between gas transfer velocity and wind speed was derived from the DMS flux measurements; this relationship was in close agreement with a parameterization derived from relaxed eddy accumulation measurements of DMS over the northeastern Pacific Ocean. However, the GasEx-2001 relationship results in gas transfer rates that are a factor 2 higher than gas transfer rates calculated from a parameterization that is based on coincident eddy correlation measurements of CO2 flux. The measurement precision of both the profiling and eddy correlation techniques applied during GasEx-2001 is comparable; the two gas transfer data sets are in agreement within their uncertainty. Differences in the number of samples and the wind speed range over which CO2 and DMS fluxes were measured are likely causes for the observed discrepancy.