Toward Improved Numerical Forecasting of Wintertime Stable Boundary Layers Erik Crosman 1 , John Horel 1 , Chris Foster 1 , Erik Neemann 1 , Brian Blaylock 1 , Lance Avey 2 1 University of Utah Department of Atmospheric Sciences 2 Utah Division of Air Quality
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Toward Improved Numerical Forecasting of Wintertime Stable Boundary Layers
Toward Improved Numerical Forecasting of Wintertime Stable Boundary Layers. Erik Crosman 1 , John Horel 1 , Chris Foster 1 , Erik Neemann 1 , Brian Blaylock 1 , Lance Avey 2 1 University of Utah Department of Atmospheric Sciences 2 Utah Division of Air Quality. Motivation. - PowerPoint PPT Presentation
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Toward Improved Numerical Forecasting of Wintertime Stable Boundary Layers
Erik Crosman1, John Horel1, Chris Foster1, Erik Neemann1, Brian Blaylock1, Lance Avey2
1University of UtahDepartment of Atmospheric Sciences
2Utah Division of Air Quality
Motivation• Persistent cold air pools forced by small-scale processes (e.g. ,
turbulence) and by large-scale processes (e.g., subsidence and fronts
• Cold air pools and attendant air quality are particularly difficult to forecast—large ‘bust’ potential for high temperatures and clouds
• Need to improve NWP in stable wintertime conditions
Why are Cold Air Pools so Difficult to Model?
Craig Clements photo Jim Steenburgh photo
Erik Crosman photo
Source: Bourne (2008)
MODELOBS
• Poor model representation of• Snow cover, snow albedo,
skin temperature, and vegetation density
• Initialization• Low clouds (Gultepe et al.
2014)• Stable stratification ,
turbulence and mix-out by PBL schemes (Baklanov et al. 2011; Holtslag et al. 2013)
Example CAP Forecast ChallengeAREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND JUNCTION CO 944 PM MST SAT NOV 30 2013 .UPDATE... ISSUED AT 940 PM MST SAT NOV 30 2013
HAVE ADJUSTED AREAS OF FOG FOR TONIGHT THROUGH SUNDAY WITH FOG MAINLY IN THE VALLEY BOTTOMS AND ALONG THE SLOPES OF THE WESTERN MOUNTAINS. SOUNDINGS OVER THE LAST 36HRS AT GJT SHOW THE STRATUS LAYER NEAR 7500FT SO HAVE ADDED FOG TO THE SLOPES DEFINED BY 7-8KFT. THE NEW NAM IS NOT RECOGNIZING THE BOUNDARY LAYER FOG SO ITS FORECAST TEMPS ARE TOO HIGH FOR THE WESTERN VALLEY SITES.
1 December 2010- 7 February 2011The Bingham Canyon Mine
Experiment
Overview and Air Quality: Silcox et al. 2012; Young 2013; Lareau et al. 2013Whiteman et al. 2014; Whiteman and Hoch 2015Large-Scale Dynamics: Lareau et al. 2013; Lareau and Horel, 2014, Lareau and Horel, 2015Numerical Modeling and Local Forcing: Wei et al. 2013; Lu and Zhong 2014; Neemann et al. 2014. Lareau and Horel, 2015; Crosman and Horel 2015
Photo: Erik CrosmanCloud Ice Cloud IceCloud Water Cloud Water
Before After
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Ice Fog
LES ΔX 250 m
PCAPSOBSERVATIONS
ΔX 1335 m
Large-Eddy Simulations of CAPsDepth
Duration
Clouds
Physics
CAP too shallow
Ɵ PBL: YSU
Ɵ PBL: none
PCAPS Ɵ observations
Important To verify verticalprofiles
PBL: YSU ΔX = 1.33 kmLES: ΔX = 0.250 km
0
12
6WindSpeed(m s-1)
2-mTemp(ᵒC)
GreatSalt Lake Salt
Lake Valley
Salt Lake Valley
GreatSalt Lake
3
9
10
0
5
-5
sltrib.com
Toxic soup continues… Time to exercise!
• CAP simulations sensitive to --Land use and snow cover treatment --Initialization time --Cloud microphysics parameterizations --Turbulence parameterization (LES vs PBL)
• Future Work --Implementing ice fog and aerosol-aware Thompson schemes (Kim et al. 2014;
Thompson & Eidhammer 2014) --Testing several new PBL schemes and additional LES simulations --Additional research regarding albedo/snow treatment, land use, initialization