Development and Evaluation of New Monin–Obukhov and Bulk Richardson Parameterizations to Improve the Representation of Surface–Atmosphere Exchange in Weather Forecasting Models

For decades, Monin-Obukhov Similarity Theory (MOST) has been used for representing surface-atmosphere exchange in weather forecasting models. However, there is still no consensus regarding the functional forms of MOST relationships or the limitations of this theory. Thus, an alternative to MOST is using the bulk Richardson number (R_ib) as a stability term, rather than the dimensionless stability length, ζ, used in MOST. The Land-Atmosphere Feedback Experiment (LAFE) provided an ideal testbed in which to evaluate MOST parameterizations and to determine whether using gradients computed using R_ib as a stability term help better explain observations than flux-based scalings derived from MOST. In the present study we investigated relationships between ζ and the dimensionless wind shear gradient (Φ_m), temperature gradient (Φ_h), and moisture gradient (Φ_q). We also investigated relationships between R_ib and the friction coefficient (C_u), heat-transfer coefficient (C_t), and moisture-transfer coefficient (C_r). We evaluated the new functions developed using independent data sets obtained during the Verification of the Origins of Rotation in Tornadoes Experiment-Southeast (VORTEX-SE). We found that using R_ib functions to compute wind, temperature, and moisture yielded better agreement with the VORTEX-SE observations instead of using ζ functions derived from MOST. These findings underscore limitations in MOST and motivate the need to consider transitioning toward using R_ib parameterizations to represent surface-atmosphere exchange in weather forecasting models.