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CHARACTERIZING THE DISPERSIVE STATE OF CONVECTIVE BOUNDARY LAYERS FOR APPLIED DISPERSION MODELING
Citation:
Irwin, J. AND J. Paumier. CHARACTERIZING THE DISPERSIVE STATE OF CONVECTIVE BOUNDARY LAYERS FOR APPLIED DISPERSION MODELING. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-90/362 (NTIS PB91163766).
Description:
Estimates from semiempirical models that characterize surface heat flux, mixing depth, and profiles of temperature, wind, and turbulence are compared with observations from atmospheric field Studies conducted in Colorado, Illinois, Indiana, and Minnesota. In addition, for wind and turbulence profiles sodar observations are compared with tower measurements at the Colorado site. he median surface heat flux, as calculated using surface-layer flux-profile relationships and an energy budget model, was consistently overestimated from 20% to 80%. everal mixing depth models were evaluated: ne that integrates the hourly surface heat flux and friction velocity, another that solves for the time rate of change of profiles of virtual potential temperature, and a third that is an interpolation scheme used by the U.S. Environmental Protection Agency in regulatory dispersion models. or the late afternoon, the first and third listed performed noticeably better than the second; 80% to 90% of the estimates from the two models were within 40% of the observed values. or the morning hours after sunrise, the first model performed twice as well as the other models, but all were less accurate. emperature estimates from surface-layer flux-profile relationships compared well with observations within the mixed layer, but were too low for the inversion layer aloft. Mind profiles were derived using surface-layer flux-profile relationships, a wind-profile power-law based on Pasquill stability category, and sodar measurements. he soda measurements were superior to both types of model estimates. urbulence profiles were derived from sodar measurements and from semiempirical similarity relationships based on mixing depth and Obukhov length. The scatter in the comparisons with the soda observations is twice that seen In the comparisons with empirical profile relationships. Overall, it appears that uncertainty of as low as 20% to 30% in the characterization of the diffusion meteorology is the exception rather than the rule.