Publications

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2012
Zhang, Y, Zhang X.  2012.  Ocean haline skin layer and turbulent surface convections. Journal of Geophysical Research-Oceans. 117   10.1029/2011jc007464   AbstractWebsite

The ocean haline skin layer is of great interest to oceanographic applications, while its attribute is still subject to considerable uncertainty due to observational difficulties. By introducing Batchelor micro-scale, a turbulent surface convection model is developed to determine the depths of various ocean skin layers with same model parameters. These parameters are derived from matching cool skin layer observations. Global distributions of salinity difference across ocean haline layers are then simulated, using surface forcing data mainly from OAFlux project and ISCCP. It is found that, even though both thickness of the haline layer and salinity increment across are greater than the early global simulations, the microwave remote sensing error caused by the haline microlayer effect is still smaller than that from other geophysical error sources. It is shown that forced convections due to sea surface wind stress are dominant over free convections driven by surface cooling in most regions of oceans. The free convection instability is largely controlled by cool skin effect for the thermal microlayer is much thicker and becomes unstable much earlier than the haline microlayer. The similarity of the global distributions of temperature difference and salinity difference across cool and haline skin layers is investigated by comparing their forcing fields of heat fluxes. The turbulent convection model is also found applicable to formulating gas transfer velocity at low wind.

Zhang, X.  2012.  Contribution to the global air-sea CO2 exchange budget from asymmetric bubble-mediated gas transfer. Tellus Series B-Chemical and Physical Meteorology. 64   10.3402/tellusb.v64i0.17260   AbstractWebsite

Quantifying air-sea gas exchange is an essential element for predicting climate change due to human activities. Air-sea gas exchanges take place through both the sea surface and bubbles formed during wave breakings. Bubble-mediated gas transfers are particularly important at high wind regions. Bubble-mediated gas transfers are separated into symmetric and asymmetric transfers. Their transfer fluxes are respectively proportional to the gas concentration difference between the atmosphere and ocean surface water, and to the atmospheric gas concentration alone. To quantify the role of asymmetric transfers in the global carbon dioxide (CO2) transfer budget, a parameterisation scheme of asymmetric transfer is developed, which is constrained by gas equilibrium supersaturation in the ocean surface. By establishing a bound for the global mean gas equilibrium supersaturation in ocean surface water, we found that the global ocean uptake by bubble-mediated asymmetric gas transfer is a substantial part of the total air-sea CO2 uptake budget (over (2)0%). It is found that, over the past half century, the global asymmetric ocean CO2 uptake has increased about a total of 40% on a steadily trend, as a consequence of the increasing atmospheric CO2 concentrations.