Fine Scale Meteorology & Air Quality Models - School of Architecture ...

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ASI2_Lecture 3_7/12/2011 TERRA: Aug 4 2006 @ 1720 UTC WRF V3.2 (NOAH BEP_BEM BouLac) SW Down Base 2238 PBL Base 2238 Martilli’s filter scheme applied to base case. SW Down Filtered Base 2238 PBL Filtered Base 2238 Objective: To reduce amount of model noise ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 Preliminary Study Findings • Low level convective features are frequent and regular features in study area for weakly forced systems based on cloud fields from satellite) • Convective features are resolvable with fine scale, less so as grid size increases, characteristics depend on physics options • Modeled simulations shows convective features to be quasi stationary • Spatial characteristic are sensitive to choice of physics options. Presents a significant challenge to modeling air quality at fine scales • Ad hoc filtering approaches might be useful towards reducing model “noise” • Concern: What is resolved, what is noise ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 20
ASI2_Lecture 3_7/12/2011 erturbations nique inks to etup xploration Taking the model’s • Fine scale modeling enters the “Terra Incognita” regime • Given that mesoscale modeling systems have many operating options, how are the resulting simulation dependent on the user selection of model options. • Need to understand the properties of modeling systems dependence on the properties of their individual components and their linkages. • Ad hoc modeling group is currently undertaking this study, preliminary results follows. • Perform & explore model sensitivity studies including: Model physics, numerics, time steps, grid size, filtering ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 Numerical Considerations: Horizontal Diffusion Standard configuration of WRF has in the horizontal the Smagorinsky scheme K h s C x 2 s C 0.4 2 u v 0.25 2 2 x y ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 2 2 u v y x In Martilli’s simulations, with DX=1km, this gives K h values of the order of 100-200 m2/s Standard MM5 has in the horizontal (see Xu et al. MWR 2001) K K h H 0 K H 0 3. 10 2 2 2 2 u v u v Cs x 0.25 2 2 x y y x 3 x t 2 2 600. m 2 //s s For Dx=1000.m and Dt=5s (Martilli’s case) “the background term K H0 is dominant at all levels and locations throughout the simulation time” Xu et al. MWR 2001 21
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