1. Erik Crosman 1, John Horel 1, Chris Foster 1, Erik Neemann 1 1 University of Utah Department of Atmospheric Sciences Toward Improved NWP Simulations of Utah Basin Cold Air Pools 12.5 33 rd Conference on Alpine Meteorology 31 Aug – 4 Sept 2015, Innsbruck, Austria

2. Recent Utah Wintertime Cold Pool Research The Persistent Cold Air Pool Study (PCAPS) The Bingham Canyon Mine Experiment Overview and Air Quality: Silcox et al. 2012; Young 2013; Lareau et al. 2013 Whiteman et al. 2014; Whiteman and Hoch 2015; Young and Whiteman 2015 Large-Scale Dynamics: Lareau et al. 2013; Lareau and Horel 2014; Lareau and Horel 2015 Numerical Modeling and Local Forcing: Wei et al. 2013; Lu and Zhong 2014; Neemann et al. 2014. Lareau and Horel 2015; Crosman and Horel 2015a,b Uintah Basin (O 3 ): Uintah Basin Wintertime Ozone Study (UBWOS) Salt Lake Valley (PM 2.5 ):

3. Complex Utah Basins Cache Valley Utah Valley Uintah Basin Great Salt Lake Basin Salt Lake Valley 25 km

4. Basic Weather Features Associated with Cold Air Pools: Well-Understood H High pressure Cold air pool Warmer air aloft Light winds Pollutants

5. Critical Weather Details Associated with Poor Winter Air Quality: Difficult to Simulate Clouds Surface fluxes Turbulent Mixing Depth of polluted layer Transport Pollution concentrations Improper Surface State

6. Critical Weather Details Associated with Poor Winter Air Quality: Difficult to Simulate Clouds Snow Cover and Land Use Turbulent Mixing Depth of polluted layer Transport Pollution concentrations Inadequate boundary-layer and cloud parameterizations

7. Improving Cold Air Pool Simulations in the Weather Research and Forecasting Model (WRF) Grid spacing = 12 km Grid spacing = 4 km Grid spacing = 1.3 km Grid spacing 250 m -- Surface state and initialization --Boundary-layer physics MYJ PBL (mesoscale) No PBL (LES) RRTMG radiation NOAH LSM Thompson microphysics

8. Improve Snow Cover Initialization Thin, tenous snow pack in Utah Basins (< 5-10 cm) Snow physics models undeveloped for shallow snowpack Ice fog deposition Spatially inhomogeneous snow fall and melt rates 0-5 cm

9. Simulating Snow Effects Better Before correction After correction Albedo DepthVegetation

10. 2 0-2-12 -10 -8 -4-6 °C SNOWNo Snow Mean 2-m Temperatures Sensitivity to Snow Cover 10 -7.7 °C -9.7 °C -2.1 °C -628 -2.0 °C -4.5 °C Salt Lake Valley Uintah Basin 0-4 Neemann et al. 2014 Daytime SNOW - CONTROLNighttime SNOW - CONTROL -246

11. Improve Land Use Specification Default USGS Land Use outdated NLCD 2011 Implemented --40% increase in urban area --30% decrease in lake surface Additional changes required based on satellite imagery (frozen lake, dry lake) and surface albedo measurements Default WRF After modifications

12. WRF CAP Sensitivity to Land Use 9 Day Average 2-m Temperature Difference USGS minus NLCD

13. Cloud water 2 m temp Low clouds and fog after ~2 days warm lake LAKE+3 Elevation (m) cold lake LAKE-3 (g kg) (⁰C) Impact of Great Salt Lake on Temperature and Low Clouds Salt Lake Valley 1280 3500 2400 Great Salt Lake

14. Liquid Clouds vs. Ice Clouds Over the entire model run, liquid clouds produced an average of 7-20 W/m 2 more longwave energy than ice clouds in the Uintah Basin 14 Improve Cloud Specification Neemann et al. (2015)

15. LES ΔX 250 m ΔX 1335 m Improve Turbulent Mixing: Large-Eddy Simulation of CAP Depth Duration Clouds Physics CAP too shallow Ɵ PBL: YSU Ɵ PBL: none PCAPS Ɵ observations Important To verify vertical profiles Crosman and Horel (2015)

16. PBL: YSU ΔX = 1.33 km LES: ΔX = 0.250 km 0 12 6 Wind Speed (m s -1 ) 2-m Temp (ᵒC) Great Salt Lake Salt Lake Valley Salt Lake Valley Great Salt Lake 3 9 10 0 5 -5 sltrib.com Toxic soup continues… Time to exercise!

17. Summary and Future Work Surface state, snow cover, and land use specification critical for simulating Cold Air Pools (CAPs) CAP simulations also sensitive to turbulent mixing and cloud algorithms Simulations have been applied to a range of CAPs to better understand meteorological evolution and processes More advancements in NWP of CAPs are needed