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.

2007
Zhang, X, Cai WJ.  2007.  On some biases of estimating the global distribution of air-sea CO2 flux by bulk parameterizations. Geophysical Research Letters. 34   10.1029/2006gl027337   AbstractWebsite

It is important to examine the parameterizations used in calculating air-sea exchange fluxes as they are essential in developing global carbon models and in carbon budget calculations. We quantify the potential biases involved in the parameterizations. Adopting a non-zero gas transfer velocity for low wind areas results in a significant increase in the CO2 flux in equatorial regions with a net increase of +0.2 Pg C yr(-1) in the total sea-air global flux. The ocean "cool skin temperature'' effect on CO2 flux estimation is found to be an order of magnitude smaller than early estimations. The previously unknown salty-skin effect has an opposite contribution that cancels the cool-skin effect. Comparing different wind speeds derived from satellite data and Global Circulation Models (GCM), the most significant divergence is found at the low wind equatorial regions regarding the CO2 flux estimation.