Using eddy covariance to measure the dependence of air–sea CO<sub>2</sub> exchange rate on friction velocity
Parameterisation of the air–sea gas transfer velocity of CO<sub>2</sub> and other trace gases under open-ocean conditions has been a focus of air–sea interaction research and is required for accurately determining ocean carbon uptake. Ships are the most widely used platform for air–se...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/4297/2018/acp-18-4297-2018.pdf |
| Summary: | Parameterisation of the air–sea gas transfer velocity of CO<sub>2</sub> and
other trace gases under open-ocean conditions has been a focus of air–sea
interaction research and is required for accurately determining ocean carbon
uptake. Ships are the most widely used platform for air–sea flux measurements
but the quality of the data can be compromised by airflow distortion and
sensor cross-sensitivity effects. Recent improvements in the understanding of
these effects have led to enhanced corrections to the shipboard eddy
covariance (EC) measurements.</br></br>Here, we present a revised analysis of eddy covariance measurements of air–sea
CO<sub>2</sub> and momentum fluxes from the Southern Ocean Surface Ocean Aerosol
Production (SOAP) study. We show that it is possible to significantly reduce
the scatter in the EC data and achieve consistency between measurements taken
on station and with the ship underway. The gas transfer velocities from the
EC measurements correlate better with the EC friction velocity (<i>u</i><sub>*</sub>) than
with mean wind speeds derived from shipboard measurements corrected with an
airflow distortion model. For the observed range of wind speeds
(<i>u</i><sub>10 N</sub> = 3–23 m s<sup>−1</sup>), the transfer velocities can be
parameterised with a linear fit to <i>u</i><sub>*</sub>. The SOAP data are compared to
previous gas transfer parameterisations using <i>u</i><sub>10 N</sub> computed
from the EC friction velocity with the drag coefficient from the Coupled
Ocean–Atmosphere Response Experiment (COARE) model version 3.5.
The SOAP results are consistent with previous gas transfer studies, but at
high wind speeds they do not support the sharp increase in gas transfer
associated with bubble-mediated transfer predicted by physically based
models. |
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| ISSN: | 1680-7316 1680-7324 |