application of new parameterization to satellite scatterometer data
new air-sea flux parameterization for CO2 fluxes
seasonal and annual mean CO2 estimates
Beschreibung:
C-band microwave sea surface radar backscatter observations from the FINO-2 tower in the western Baltic are analyzed with respect to their relevance for air-sea CO2 transfer velocity parameterizations. The scatterometer measurements observed from a height of 25 m above the sea surface using a multifrequency scatterometer instrument of the University of Hamburg were obtained quasi-simultaneously with eddy covariance CO2 flux measurements. Both data sets are merged here to derive a gas transfer velocity parameterization based on radar backscatter measurements. At the location of the FINO-2 tower, the resulting time-averaged gas transfer velocity amounts to 26.95 cm/hr. In combination with ΔPCO2 measurements available from the vicinity of the FINO-2 platform, a time-mean CO2 flux of 0.23 μmol·m−2·s−1 into the Baltic was estimated. Applied to monthly mean satellite-based C-band ASCAT scatterometer data, the newly derived gas transfer velocity parameterization provides estimates of seasonal and annual mean global maps of air-sea transfer velocities. The new results agree in their general pattern with previous estimates using wind speed parameterization. However, the backscatter-based transfer velocities appear smaller at higher latitudes. Globally averaged air-sea CO2 fluxes would thereby be reduced by 20%. To what extent this is a robust result, or if it depends on the fact that the training data set did not represent conditions, has to be investigated in the future.