Systematic errors in global air-sea CO2 flux caused by temporal averaging of sea-level pressure

[摘要] Long-term temporal averaging of meteorological data, such as wind speed andair pressure, can cause large errors in air-sea carbon flux estimates. Otherresearchers have already shown that time averaging of wind speed data createslarge errors in flux due to the non-linear dependence of the gas transfervelocity on wind speed (Bates and Merlivat, 2001). However, in general, windspeed is negatively correlated with air pressure, and a given fractionalchange in the pressure of dry air produces an equivalent fractional change inthe atmospheric partial pressure of carbon dioxide (pCO_2air). Thuslow pressure systems cause a drop in pCO_2air, which together withthe associated high winds, promotes outgassing/reduces uptake of CO₂ fromthe ocean. Here we quantify the errors in global carbon flux estimates causedby using monthly or climatological pressure data to calculatepCO_2air (and thus ignoring the covariance of wind and pressure)over the period 1990-1999, using two common parameterisations for gastransfer velocity. Results show that on average, compared with estimates madeusing 6 hourly pressure data, the global oceanic sink is systematicallyoverestimated by 7% (W92) and 10% (WM99) when monthly mean pressure isused, and 9% (W92) and 12% (WM99) when climatological pressure is used.

[学科分类] 大气科学