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Observations of Great Salt Lake Breezes During Salt Lake Valley Persistent Cold Air Pools

Observations of Great Salt Lake Breezes During Salt Lake Valley Persistent Cold Air Pools. `. Erik Crosman, John Horel, Neil Lareau, and Xia Dong University of Utah Department of Atmospheric Sciences. 15 th AMS Conference on Mountain Meteorology Steamboat Springs, CO

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Observations of Great Salt Lake Breezes During Salt Lake Valley Persistent Cold Air Pools

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  1. Observations of Great Salt Lake Breezes During Salt Lake Valley Persistent Cold Air Pools ` Erik Crosman, John Horel, Neil Lareau, and Xia Dong University of Utah Department of Atmospheric Sciences 15th AMS Conference on Mountain Meteorology Steamboat Springs, CO Paper 8.3 Tuesday, 21 August 2012

  2. Part of Larger Effort to Improve Understanding of Summertime and Wintertime Sea and Lake Breezes Summer 2009 Great Salt Lake Breeze Undergraduate Field Study Winter 2010-2011 Persistent Cold Air Pool Study • Great Salt Lake relatively ideal environment for observing lake breezes • Large variability in atmospheric, land and lake surface state • Lake breezes for small and medium sized lakes less well-understood than sea breezes • Very few observations of mid-latitude wintertime lake breezes • No previous studies on lake breezes occurring during wintertime cold air pools

  3. The Persistent Cold Air Pool Study (PCAPS) Unprecedented wintertime observations! Lareau,N., E.Crosman, C.D.Whiteman, J.D.Horel, S.W.Hoch, W.O.J.Brown, and T.W.Horst,2012:ThePersistent Cold Air Pool Study Bulletin of the American Meteorological Society In press Great Salt Lake 4,400 km2 Wasatch Mountains Salt Lake Valley ~1,000 km2 Oquirrh Mtns 1 December 2010-5 February 2011

  4. Research Questions 1. What are the characteristics of and processes controlling winter lake breezes during persistent cold air pools? Great Salt Lake Lake Breeze Front PCAPS IOP1 5 December 2010

  5. Research Questions Salt Lake Valley Lake 2. How do the lake breezes impact persistent cold air pools? PCAPS IOP5 7 January 2011 Photo Dave Bowling

  6. Sensitivity of Summer Lake Breezes to Land Surface Sensible Heat Flux MODIS July 17 2009 Mtns Great Salt Lake May 17 July 17 Salt Lake City Mtns High heat flux MODIS May 17 2009 Great Salt Lake Medium heat flux Salt Lake City Land Surface Skin Temperature (°C)

  7. Low Flux LES Simulation ‘Winter’ 100 W m-2 z (m) High Flux LES Simulation ‘Summer’ Lake Lake km km Land Land 400 W m-2 z (m) 0 20 40 60 80 100 120 0 20 40 60 80 100 120 Crosman and Horel 2010 Sea and Lake Breezes: A Review of Numerical StudiesBLM 137:1-29 u ms-1 Crosman and Horel 2012 Idealized Large-Eddy Simulations of Sea and Lake Breezes: Sensitivity to Lake Diameter, Heat Flux and Stability BLM 144(3):309-328

  8. Observations of Typical Summer vs. Winter Great Salt Lake Breezes 3 Feb 2011 ‘PCAPS Winter’ 17 July 2009 ‘Summer’ 10 5 0 Summer Winter Cross-Coast Breeze Wind Speed (m s-1) 5-8 2-3 Depth (m) 600 m200 m Duration (hr) 10 hr6 hr

  9. Not Expecting ‘Enhanced’ Lake Breezes During PCAPS! • Wind speed, duration, and depth comparable to summer in several cases • Lake breeze surface frontal contrast and inland movement higher than summer IOP3 13 December 2010 • Lake/land ΔT of 7 ⁰C • Lake breeze wind speeds ~4-5 m s-1 ⁰C ⁰C • Lake breeze depth near shoreline >500 m • Inland movement ~10 km h-1 ⁰C ⁰C IOP3 13 December 2010

  10. Processes Contributing to Great Salt Lake Summertime Breezes • Heat Flux (insolation, soil moisture) • Background wind (occurrence or not and inland movement) Great Salt Lake Salt Lake Valley

  11. Processes Contributing to Great Salt Lake Wintertime Breezes During CAPs Winter lake breezes during PCAPS complex due to: 1. Weak solar forcing allows other processes (e.g., lake heat flux, cold air drainage) to become significant 2. Interactions between solar heating, boundary-layer stable layers and background winds result in mixing and horizontal temperature gradients 3. When these processes favorably combine the lake breeze is enhanced mixing Insolation Valley wind channeling Ɵ + ΔƟ stability Ɵ Great Salt Lake Salt Lake Valley Snow cover Clouds and fog Cold air drainage pooling Lake heat flux

  12. 12 Dec 13 Dec IOP3 12-13 December 2010 Air over Valley Lake breeze front Temperature (⁰C) Air over Lake 5 11 17 23 17 5 11 Time (MST) 5 m s-1 5 m s-1 mixing Insolation COLD Valley wind channeling Ɵ + ΔƟ stability Ɵ Great Salt Lake COLD Salt Lake Valley WARM Snow cover Clouds and fog Cold air drainage pooling Lake heat flux

  13. Low-Budget Research Aircraft: Motorized Paraglider Valley Glider shoreline 5 m s-1 IOP3 13 December 2010

  14. Research Questions Salt Lake Valley Lake 2. How do the lake breezes impact persistent cold air pools? Photo Dave Bowling

  15. Large Horizontal Variations in Salt Lake Valley Persistent Cold Air Pools Occur During Lake Breezes Lake Breezes Difference in BL temperature (⁰C) between Valley and Near Lake Day of January 2011

  16. Lake Breeze ‘Recharge’ • Influences CAP intensity and • duration • 8 documented cases • Lake a ‘reservoir’ of cold air Ɵ (K) Ɵ (K) IOP9 26-27 Jan 2011 26 Jan 27 Jan 292 292 1100 1100 287 287 Height (m) Height (m) 500 500 0 0 282 282 23 23 05 05 11 11 17 17 23 23 17 17 Time (MST) 26 Jan 27 Jan Time (MST) Estimating mixed-layer heights (Horel et al. previous talk 8.2)

  17. Lake Breezes ‘Recharge’ Persistent Cold Air Pool Boundary Layer U (ms-1) U (ms-1) IOP9 26-27 Jan 2011 26 Jan 27 Jan 6 6 1100 1100 Lake breeze winds 3 3 Height (m) Height (m) 500 500 less daytime heating near lake 0 0 0 0 23 23 05 05 11 11 17 17 23 23 17 17 Time (MST) 26 Jan 27 Jan ‘Pulsing’ nocturnal drainage flows More nocturnal cooling over valley Time (MST)

  18. Great Salt Lake Lake Breezes Modulate Clouds, Fog MODIS Terra ~IOP9 18 UTC 28 Jan 2011 Great Salt Lake Salt Lake Valley PCAPS IOP5 Jan 6 2011 fog

  19. Lake Breezes Modulate Valley Pollutants Convergence and Advection IOP9 27 Jan 2011 Noon 2 pm Noon 2 pm Wind Speed (m s-1)

  20. Summary • Winter lake breezes typically ~1/3 speed, depth of summer case • Winter lake breeze forcing mechanisms complex and variable • Several ‘enhanced’ wintertime lake breezes unexpectedly observed during PCAPS • Afternoon lake breezes were found to ‘recharge’ cold air in the lowest 200-800 m of Salt Lake Valley boundary layer • Lake breezes play role in cold air pool fog and low cloud occurence • Lake breeze passage lowered pollutant concentrations within SLV

  21. Questions? Photo Sebastian Hoch

  22. Observed Spectrum of Winter GSL Breezes Less complex More complex Weakest Strongest surface heat fluxes (land surface) surface heat fluxes background winds surface heat fluxes -land surface -lake surface background winds -terrain channeling and blocking -differential mixing stability cold air pooling clouds Generally discussed spectrum

  23. 10 Factors That Impact Sea and Lake Breezes mixing Lake surface sensible heat flux Nocturnal drainage cold pool Crosman and Horel 2010 Sea and Lake Breezes: A Review of Numerical StudiesBLM 137:1-29

  24. Summer Great Salt Lake Breeze ~2 pm 17 July 2009 • High land surface sensible heat flux drives lake breeze circulations Great Salt Lake snow Wasatch Mtns Salt Lake Valley • Background synoptic wind modulates occurrence, intensity and inland extent Salt Lake Valley Mtns Tooele Valley Stansbury Mtns Land Surface Skin Temperature (°C)

  25. Lake Breezes Modulate SLV Cloud Cover Photo: Sebastian Hoch 18 UTC IOP9 28 Jan 2011 MODIS Terra ~18 UTC 28 Jan 2011 Great Salt Lake High RH Salt Lake Valley Low RH Utah Valley

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