Monday, 23 January 2017
4E (Washington State Convention Center )
Sensitivity of numerical simulations of an ice fog event to the planetary boundary layer (PBL) and the surface layer (SL) parameterization schemes is examined with the Weather Research and Forecasting (WRF) model. An ice fog episode, observed in Heber Valley, Northern Utah over complex terrain region during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program, is studied. Numerical simulations and observations are compared during the day of fog occurrence under both unstable and stable surface layer conditions. Results show that WRF model has significant uncertainty in the simulation of the near-surface atmospheric conditions during the nighttime, compared with these during the daytime. The simulation is very sensitive to the choices and configurations of both PBL and SL schemes. Specifically, it is found that the SL scheme could largely influence the performance of the PBL scheme, especially during the nighttime period. Further diagnoses indicated that the model’s inability of accurate representation of surface fluxes in SL scheme could be an important source of errors for the fog prediction. The SL scheme not only influences the development of daytime mixed layer but is also crucial to the stable layer during the night time. PBL scheme, however, has less contribution to the nighttime simulation when compared to SL scheme. Overall, uncertainties in the SL parameterization scheme are crucial to the fog simulation.
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