The surface flux calculation method proposed by Louis (1979) is extended by allowing momentum and heat to have different roughness lengths (z0 and zT respectively). Our approach is to extend the traditional analysis by a more careful consideration of potential temperature structure near the surface. This consideration leads to a redefinition of the bulk Richardson number. For bulk transfer coefficients, our method shows a significant improvement over the original Louis method when compared with the theoretical surface-layer model applied to rough surfaces. Numerical experiments simulating sea breezes in 2D show that our extension is crucially important in simulating light wind and low humidity conditions.
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