DEPENDENCE OF THE MONIN-OBUKHOV STABILITY PARAMETER ON THE BULK RICHARDSON-NUMBER OVER THE OCEAN

Recent measurements made onboard the R/P FLIP in the San Clemente Ocea n Probing Experiment in September 1993 and onboard the R/V Moana Wave during Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Respo nse Experiment are used to evaluate the direct dependence between the Monin-Obukhov stability parameter (ratio of height to Obukhov length) zeta and the bulk Richardson number Ri(b) derived from standard meteor ological mean observations of water surface temperature, wind speed, a ir temperature, and humidity. It is found that in the unstable marine surface layer, zeta = C Ri(b)(1 + Ri(b)/Ri(bc),)(-1), where the numeri cal coefficient C and the saturation Richardson number Ri(bc) are anal ytical functions of the standard bulk exchange coefficients. For measu rements at a height of 10-15 m, C is about 10 and Ri(bc) is about -4.5 . Their values are insensitive to variations of Ri(b) and zeta over th ree decades. Thus, a simple dependence between zeta and Ri(b) has a mu ch wider range of applicability than previously believed. The authors show that this behavior is the result of the effects of ''gustiness'' driven by boundary layer-scale convective eddies. The derived relation ship can be used as a first guess for zeta in bulk flux routines and r educes or eliminates the need for lengthy iterative solutions. Using t his approximation yields errors in the latent heat flux of a few watts per square meter, compared to the full iterative solution.