Help - Bulk Richardson Number

The bulk Richardson number (BRN) is a ratio of buoyancy to vertical shear: BRN = (MLCAPE) / 0.5 * (U)**2 where U = the wind speed difference between the density weighted 0-6 km mean wind and the lowest 500 m mean wind. The BRN is meant to estimate the balance between vertical shear and buoyancy, with low BRN values suggestive of vertical shear that is too strong relative to the buoyancy, and large BRN values are suggestive of multicell clusters. Intermediate BRN values favor sustained supercells. BRN values in the range of 10-45 (dimesionless) have been associated with supercells via numerical simulations. Close proximity soundings reveal supercell environments with larger CAPE and larger resultant BRN values (in the range of 50-100) than suggested by the original modeling work of Weisman and Klemp (1982).

Weisman, M. L., and J. B. Klemp, 1982: The dependence of numerically simulated convective storms on vertical wind shear and buoyancy. Mon. Wea. Rev., 110, 504-520.

Thompson, R. L., R. Edwards, J. A. Hart, K. L. Elmore, and P. Markowski, 2003: Close proximity soundings within supercell environments obtained from the Rapid Updage Cycle. Wea. Forecasting, 18, 1243-1261.

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