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.

NAM OBS

Types of Persistent Cold Air Pools

Craig Clements photo

Cloudy Dry

Jim Steenburgh photo

Erik Crosman photo

Heterogeneous

No two CAPs are alike!

Numerical model may struggle with one type more than others!

Different physical processes important for different CAPs

pre-mix out cloudy

Multi-levelElevated inversion nocturnal

cloudy

Lareau et al. 2013 BAMS

• PCAPS observational data available at

www.pcaps.utah.edu

Recent Utah Wintertime Cold Pool Field Campaigns

The Persistent Cold Air Pool Study (PCAPS)

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

Uintah Basin (High O3):Uintah Basin Wintertime Ozone

Study (UBWOS) December 2011- February 2012December 2012- February 2013December 2013- February 2014

Salt Lake Valley (High PM2.5):

Ongoing Work to Improve Wintertime Cold Air Pool Simulations

• Surface state characterization (e.g., snow, albedo, land use, vegetation)

• Initialization• Cloud microphysics • Boundary-layer turbulence

USGS higher albedoUSGS colder temps

WRF CAP Sensitivity to Land Use9 Day Average 2-m Temperature Difference

USGS minus MODIS

Improving WRF Snow Cover Parameterization- Idealized snow cover in Uintah Basin and mountains- Snow albedo changes- Edited VEGPARM.TBL

Allows model to achieve high albedos measured in basin

9

Snow Depth

Albedo Changes

10

Original Modified

0.62- 0.65 0.81 - 0.82

- 0.82 is average albedo measured at Horsepool during 2013 Uintah Basin Winter Ozone Study

Initialization 2Initialization 1

31 December 2010 1 January 2011 2 January 2011

WRF CAP Sensitivity to Initialization TimeIdentical simulations started 1 day apart

Obs

31 Dec1 Jan

WRF CAP Sensitivity to Initialization TimeIdentical simulations started 1 day apart

1 Jan

Uinta Mountains

Was

atch

Ran

ge

Tavaputs

Desolation Canyon

Plateau

WY

COUT

1250

1500

1750

2250

2750

3250

3750

4000

3500

3000

2500

2000

Roosevelt

MytonOuray

Horsepool

Red Wash

Vernal

WRF CAP Sensitivity to Initialization TimeIdentical simulations started 1 day apart

WRF Cloud and Fog Modifications- Microphysics modifications (Thompson)

in lowest 15 model layers (~500m):- Turned off cloud ice sedimentation- Turned off cloud ice autoconversion

to snow Results in ice-phase

dominated low clouds/fog vs. liquid-phase

Simulated Clouds

Reality

http://wwc.instacam.com/instacamimg/UBATC/UBATC_l.jpg

Photo: Erik CrosmanCloud Ice Cloud IceCloud Water Cloud Water

Before After

13

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

Summary and Future Work