Very stable marine boundary layers

Traditional methods for calculating fluxes from observations are not adequate for weak-wind, very-stable conditions and may yield grossly incorrect values. We employ record-dependent averaging time to compute better-behaved fluxes from ASIT tower data during the CBLAST Weak Wind Experiment. Definition of the mean wind vector also becomes problematic in weak wind conditions because the amplitude of mesoscale meandering of the wind vector can become larger than the mean wind speed, as defined by 30-minute or one-hour averages. We explore alternative definitions of the velocity scale.

To avoid severe self-correlation in stable conditions, a gradient-based similarity theory (e.g., Richardson number) is re-examined. The dependence of transfer coefficients and eddy diffusivities on the Richardson number and the relationship between the eddy Prandtl number and the Richardson number are examined for very stable conditions.