WELL-MIXED ATMOSPHERIC BOUNDARY LAYERS IN THE MM5 AND WRF MODELS

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WELL-MIXED ATMOSPHERIC BOUNDARY LAYERS IN THE MM5
AND WRF MODELS

• Frank P. Colby, Jr.
• Professor of MeteorologyUniversity of
  Massachusetts Lowell, Lowell, MA 01854

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Acknowledgements

• Brad Colman, SOO, Seattle NWS
• Cliff Mass, University of Washington and
  students, staff
• M.S. Student Anne McWilliams

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Outline

• Structure of a well-mixed boundary layer
• Model set-up for MM5 and WRF
• Boundary layer parameterizations in each model
• Results
• Conclusions

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Outline

• Structure of a well-mixed boundary layer
• Model set-up for MM5 and WRF
• Boundary layer parameterizations in each model
• Results
• Conclusions

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Outline

• Structure of a well-mixed boundary layer
• Model set-up for MM5 and WRF
• Boundary layer parameterizations in each model
• Results
• Conclusions

6
Outline

• Structure of a well-mixed boundary layer
• Model set-up for MM5 and WRF
• Boundary layer parameterizations in each model
• Results
• Conclusions

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Outline

• Structure of a well-mixed boundary layer
• Model set-up for MM5 and WRF
• Boundary layer parameterizations in each model
• Results
• Conclusions

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Structure of a well-mixed boundary layer

• Turbulent mixing creates approximately constant
  vertical profiles of
• potential temperature
• mixing ratio
• momentum
• Generally occurs during daytime driven by
  surface fluxes of heat and moisture

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Structure of a well-mixed boundary layer
00Z April 27, 2001 Albany, NY 72518
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Model set-up for MM5 and WRF

• MM5 Penn State University/National Center for
  Atmospheric Research Mesoscale Model, Fifth
  Generation, Version 3
• http//www.mmm.ucar.edu/mm5/mm5-home.html
• WRF Weather Research and Forecasting model,
  Version 2, ARW core
• http//www.wrf-model.org/

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Model set-up for MM5 and WRF

• MM5
• non-hydrostatic
• simple ice physics
• Grell convection
• Two grids, 60 km and nested 20 km
• 24 vertical sigma levels

• WRF
• non-hydrostatic
• simple ice physics
• Grell convection
• Single 20 km grid
• 24 vertical sigma levels

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Model set-up for MM5 and WRFMM5 20km Domain
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Model set-up for MM5 and WRFWRF Domain
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Boundary layer parameterizations in each model

• MM5
• MRF
• Blackadar
• Gayno-Seaman
• Eta (Mellor-Yamada)
• Burk-Thompson

• WRF
• MRF
• YSU
• Eta (Mellor-Yamada)

Ran 9 cases with each boundary layer, starting 12
UTC each day.
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Boundary layer parameterizations in each model

• Non-local turbulent exchange
• MRF
• Blackadar
• YSU
• TKE schemes
• Gayno-Seaman level 1.5 closure
• Burk-Thompson level 2 closure
• Eta level 2.5 closure

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Results Basic Quantities

• Mixed layer height
• Boundary layer potential temperature
• Boundary layer mixing ratio
• Mixed layers measured at 00 UTC
• 12 hour forecast

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Results Basic QuantitiesMM5

• Mixed layer height
• All but 2 of the heights were too low
• MRF, Blackadar were closest in 6 of the 9 cases
• Burk-Thompson was always the lowest, and the
  furthest from verification

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Results Basic QuantitiesMM5

• Boundary layer potential temperature
• All modeled mixed layers were colder than
  verification
• MRF, Blackadar and Gayno-Seaman were closest in
  all 9 cases
• Burk-Thompson was always the coldest and the
  furthest from verification

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Results Basic QuantitiesMM5

• Boundary layer mixing ratio
• MRF, Blackadar were closest to verification in 7
  of the 9 cases
• Burk-Thompson always had the highest boundary
  layer mixing ratio and was the furthest from
  verification in 8 of the 9

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Results Example

• Soundings from April 26, 2001 model runs

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MM5 Results Blackadar
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MM5 Results Burk Thompson
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MM5 Results Gayno-Seaman
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MM5 Results MRF
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MM5 Results Eta
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Results Basic QuantitiesWRF

• Mixed Layer Height
• All but 1 of the Heights were too low
• YSU and MRF schemes were closest
• Eta Parameterization had largest errors

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Results Basic QuantitiesWRF

• Boundary Layer Potential Temperature
• All but one of the modeled mixed layers were
  colder than verification
• YSU and MRF were closest to verification, Eta
  farthest away

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Results Basic QuantitiesWRF

• Boundary Layer Mixing Ratio
• No real trend in errors -- some boundary layers
  were too moist, some too dry
• YSU, MRF were closest to verification, Eta always
  had the biggest error

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WRF Results Eta
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WRF Results MRF
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WRF Results YSU
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Results Summary

• Differences in modeled mixed layers
• MM5 MRF, Blackadar warmer, dryer and higher
  than the other schemes Burk Thompson was always
  cooler, more moist and lower.
• WRF MRF, YSU almost always produced warmer,
  dryer and higher mixed layers than Eta

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Results Summary

• Preliminary analysis suggests that each scheme
  responds differently to the surface fluxes
• The underlying surface energy balance may be
  producing different surface fluxes

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Results Summary

• MM5 with MRF, Blackadar had slightly smaller
  height and potential temperature errors
• WRF with MRF, YSU had slightly smaller mixing
  ratio errors

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Conclusions

• MRF boundary layer produced the most accurate
  mixed layers in the MM5
• YSU scheme was slightly better than MRF in the
  WRF model

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Conclusions Absolute Error Statistics
Any Questions?