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

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ASI2_Lecture 3_7/12/2011 Summary: Fine grid modeling issues • A Conundrum: Real features of 1-10 km scales require grid resolution about an order of magnitude finer in size; however, much stochastic noise is present in current mesoscale simulations at fine scales (Terra Incognita regime). • Quasi Stationary, persistent 2-D and 3-D circulation in weakly forced flows • Simulations are physics option dependent • K H using SMAG (allows rolls), K H SMAG + Constant (supresses rolls) • Horizontal vortices and/or structures: – Become more pronounced with decreasing ∆x = 1km, 333m & 111m – Dissipate for decreasing ∆t= 6s,1s, 0.66s, 0.33s (features are non convergent) – Reaches max strength in afternoon, dissipate at night, are computationally stable • Numerical filters may helpful in reducing stochastic model noise, but there is no fundamental guidance that currently apply. • Other aspects/sensitivities, approaches still need to be explore: Even vs odd order filters. WRF LES ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 Part 3: Fine grid air quality modeling (examples CMAQ) 1 km UCP 4km Native Ozone NOx • 1 km results are significantly more textured than 4 km • The titrating effect of NOx on ozone (especially along highways and major point sources) are captured at 1km but not at 4 km • Photochemistry at 4 km results in part from overdilution of withingrid sources ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 26
ASI2_Lecture 3_7/12/2011 Dependence on UCP Ozone (1 km grid CMAQ simulations) @ 2100 GMT UCP no_UCP ∆ (UCP-no_UCP) • Significant differences in the spatial patterns shown between UCP and noUCP runs (titration effect occurs in both sets) • Flow, thermodynamics & turbulent fields differ between the UCP and noUCP simulations & contribute to differences ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 Simulations are unique to grid size: Example: Ozone: Fine vs Coarse (2100 GMT) Aggregate: 4km mean from 1km (w/ucp) Native 4 km simulation ∆ (Aggregate-Native) • Differences between Mean 4km aggregated from 1 km vs Native 4km • Accumulative and net of atmospheric processes acting on 1 km scale differs from that at 4km scale ASI 2: URBAN CLIMATE AND AIR POLLUTION School of Architecture, The Chinese University of Hong Kong, Hong Kong, 7-8 Dec 2011 27
Page 1 and 2: ASI2_Lecture 3_7/12/2011 Croucher A
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Page 5 and 6: ASI2_Lecture 3_7/12/2011 PBL scheme
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Page 11 and 12: ASI2_Lecture 3_7/12/2011 HYPOTHESIS
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Page 15 and 16: ASI2_Lecture 3_7/12/2011 Cooling Ca
Page 17 and 18: ASI2_Lecture 3_7/12/2011 Crossroads
Page 19 and 20: ASI2_Lecture 3_7/12/2011 ACM-2 BouL
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Page 23 and 24: ASI2_Lecture 3_7/12/2011 Suggested
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Page 29 and 30: ASI2_Lecture 3_7/12/2011 HCHO Histo
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