Marine Science Faculty Publications

The Impact of the QNSE-EDMF Scheme and Its Modifications on Boundary Layer Parameterization in WRF: Modelling of CASES-97

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EDMF, shallow convection, WRF model, planetary boundary layer

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In recent years, many eddy-diffusivity mass-flux (EDMF) planetary boundary layer (PBL) parametrizations have been introduced. Yet most validations are based on idealized set-ups and/or single-column models. To address this gap, this article focuses on the effect the mass-flux part has on the performance in the Quasi-Normal Scale Elimination-EDMF (QNSE-EDMF) PBL scheme in the Weather Research and Forecasting (WRF) model by comparing the results to observations from the CASES-97 field campaign. In addition, two refined versions, one introducing the parametrized clouds to the WRF radiation scheme, and the second adding a different entrainment formulation, have been evaluated.

The introduction of mass flux reduced errors in the average moisture profile, but virtual temperature and wind speed profiles did not change as much. The modelled mixed-layer depth, while still low compared to observations, was closer to observed values with the addition of mass flux. The major changes in the virtual potential temperature flux profiles were an increase in entrainment ratios and a slight decrease in surface values. Allowing for biases in the observed fluxes, modelled and observed flux profiles had a similar shape. However, the agreement among the modelled and between the modelled and observed water-vapour flux profiles and vertical flux divergence was often poor, a likely result of the model's failure to capture the timing of the morning boundary-layer water-vapour maximum. Further, both virtual potential temperature and water-vapour flux profiles display spurious spikes attributed to the way the non-local and local terms interact in the model. Adding mass-flux-based clouds to the radiation calculation improved the time-and space-averaged modelled incoming short-wave flux. The choice of the representation for entrainment/detrainment often affected the results to the same extent as adding mass flux.

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Quarterly Journal of the Royal Meteorological Society, v. 142, issue 695, p. 1182-1195