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

Thursday, 16 January 2020: 2:15 PM
211 (Boston Convention and Exhibition Center)
Temple R. Lee, NOAA/ARL/ATDD and CIMMS, Oak Ridge, TN; and M. S. Buban

Handout (3.1 MB)

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 (Rib) 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 Rib 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 (Φm), temperature gradient (Φh), and moisture gradient (Φq). We also investigated relationships between Rib and the friction coefficient (Cu), heat-transfer coefficient (Ct), and moisture-transfer coefficient (Cr). 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 Rib 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 Rib parameterizations to represent surface-atmosphere exchange in weather forecasting models.
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