Systematic errors in global air-sea CO<sub>2</sub> flux caused by temporal averaging of sea-level pressure
Long-term temporal averaging of meteorological data, such as wind speed and air pressure, can cause large errors in air-sea carbon flux estimates. Other researchers have already shown that time averaging of wind speed data creates large errors in flux due to the non-linear dependence of the gas tran...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2005-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/5/1459/2005/acp-5-1459-2005.pdf |
| Summary: | Long-term temporal averaging of meteorological data, such as wind speed and air pressure, can cause large errors in air-sea carbon flux estimates. Other researchers have already shown that time averaging of wind speed data creates large errors in flux due to the non-linear dependence of the gas transfer velocity on wind speed (Bates and Merlivat, 2001). However, in general, wind speed is negatively correlated with air pressure, and a given fractional change in the pressure of dry air produces an equivalent fractional change in the atmospheric partial pressure of carbon dioxide (pCO<sub>2air</sub>). Thus low pressure systems cause a drop in pCO<sub>2air</sub>, which together with the associated high winds, promotes outgassing/reduces uptake of CO<sub>2</sub> from the ocean. Here we quantify the errors in global carbon flux estimates caused by using monthly or climatological pressure data to calculate pCO<sub>2air</sub> (and thus ignoring the covariance of wind and pressure) over the period 1990-1999, using two common parameterisations for gas transfer velocity. Results show that on average, compared with estimates made using 6 hourly pressure data, the global oceanic sink is systematically overestimated by 7% (W92) and 10% (WM99) when monthly mean pressure is used, and 9% (W92) and 12% (WM99) when climatological pressure is used. |
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| ISSN: | 1680-7316 1680-7324 |